All plants are currently out of stock as we are potting things ready for the spring.


  • Where do your plants come from?
  • How many plants do I need for my pond?
  • What is your delivery charge?
  • How long will my order take to arrive?
  • How do I choose what plants to have?
  • How large are your plants?
  • How will my order come?
  • I asked to be told when a plant was back in stock. I can see it's in stock but I haven't been notified?
  • When is the best time to add plants to my pond?
  • How do I choose soil and pots for my pond plants?
  • Do you use any pesticides?
  • Can I alter my order?
  • Can I collect my order from you?
  • What if I don't want to pot my plant but want to put it directly into the ground?
  • Which pond plants are suitable for shade?
  • Can I buy plants from you if I live in Northern Ireland?
  • Are there any plants that are suitable for ponds with ducks?
  • Do you deliver outside the UK?
  • Something else I wanted has just come into stock. Can I add it to my order?
  • Can I have pond plants in with my koi?
  • What is your returns policy?
  • Which British native plants would you recommend for a wildlife pond?
  • How do I recycle your packaging?
  • How do I hide the edge of my pond, or the edges of my pots?
  • My pond has gone green - is this normal?

Ordering and delivery

What is your delivery charge?

Delivery is £9.90 or free over £50 for all orders within the UK and the Channel Islands. 

How long will my order take to arrive?

All items should arrive within one week of your placing the order. If we are very busy and it will take longer than a week, there will be a pop up box on the website informing you of the expected time.

We will notify you the day your parcel is dispatched, telling you when to expect it.

How will my order come?

We prefer to send orders by overnight fragile courier where possible. We use APC Overnight fragile service. The courier will call at your address. If you are not in, the driver has been asked to leave the plants in any safe and shady place. If you would prefer the parcel to be left in a specific place, not to be left if there is no reply, or not to arrive on a certain date, there is a box on our website checkout where you can enter instructions for this. 

Small orders, containing three or fewer plants, may be sent by Royal Mail First Class parcels, unless the plants are very fragile types. This is because we subsidise the courier charges, but for small orders we can't do this. 

Orders going to the Highlands and Scottish islands, or the Channel Islands, will usually arrive by Royal Mail whatever their size, since couriers offer slower services and at much higher prices for these areas. We feel that using Royal Mail is the best option in these cases. 

We will email you when your order has been dispatched, telling you how it has been sent and when to expect it.

If you need to know before you order how your parcel is likely to arrive, contact us and we can help you. 

Can I alter my order?

If you need to alter your order, this can be done at any time up until you receive the "Your order has been dispatched" email. Just contact us as soon as you can and we will arrange it. 

Can I collect my order from you?

Unfortunately not. For legal reasons (insurance and planning) we cannot allow members of the public to visit the nursery.  

Can I buy plants from you if I live in Northern Ireland?

Unfortunately not. Due to the provisions of the Brexit agreement, it is no longer practical to send orders containing live plants to Northern Ireland. 

The full details are as follows; to send live plants to Northern Ireland, they would have to be removed from their pots and the soil washed off. Then we would have to book a visit from a plant health inspector to check them and issue a Phytosanitary Certificate to certify that they are free of pests and diseases. This might involve laboratory testing. Then we would have to notify the plant health authorities at the destination port in Northern Ireland five days before we plan to send them. Then they may be held up at the destination while checks are made - aquatic plants are generally more delicate than garden plants, and delays would cause them to deteriorate.

While some costs can be reclaimed from the UK government, the time involved and the risk of damage to the plants means that, regrettably, it is not practical to send individual orders to Northern Ireland any more.

Do you deliver outside the UK?

No, we do not deliver any plants outside the UK, except to the Channel Islands and the Isle of Man.

We previously sent to the EU, but due to Brexit, from 2021 sending plants to the EU became the same as sending to any other country outside the UK, i.e. each time it requires contacting the plant health authorities, applying for certificates, and possibly arranging laboratory testing of the plants. The plants may also be held up in customs in the destination country. These processes make it impractically costly and time consuming for small nurseries to send plants abroad now. The Channel Islands and the Isle of Man are covered by UK regulations, so we can still send to these places. 

Something else I wanted has just come into stock. Can I add it to my order?

Yes of course - just send us a quick email. Please include either your surname or your order number, so we know who you are, and say exactly what you would like to add to your order. We will send you a special invoice for the plants you want with free postage, which you can pay through the website checkout. Then we will combine the two orders in one parcel. 

What is your returns policy?

If you simply change your mind you may cancel your purchase at any time from when you place the order up until 14 calendar days from the day you receive the goods, without giving any reason. If you do wish to cancel, please notify us by email or phone, or fill out and submit our electronic cancellation form, which you can find towards the bottom of every page on this website. We will acknowledge receipt of your cancellation without delay. 

In this case, if you have already received the plants, please unpack them and follow the care instructions on the sheet that is with them, such as standing in a tray of water, until the return can be arranged. If you have simply changed your mind, we would usually expect you to pay the return costs, and to return the items to the address below within 14 days from the day of cancelling. If you are unsure about how to return them, just ask us. A full refund of the amount you originally paid will be issued as soon as possible and in any case not later than 14 days from the day we receive the goods back, or 14 days from the day you provide evidence that you posted them. We will make the refund using the same means of payment as you used for the initial transaction. 

If you change your mind before you receive the plants but after they have been dispatched, please contact us as soon as you can so that we can arrange to retrieve them.

If anything you have ordered is damaged or faulty in any way when it arrives, please let us know as soon as you can and we will make sure a replacement is sorted out for you.

How do I recycle your packaging?

The outer boxes we use and all newspaper, white paper, and brown paper are recyclable and biodegradable. The brown parcel tape and clear sticky tape are both biodegradable and should be placed in the general rubbish bin. All plant bags are carrier bag plastic and can be recycled - check local facilities. Any rubber bands can be re-used or placed in the general rubbish bin. Any wooden supports are made from bamboo sticks and are biodegradable. Any plastic tubs are food grade and should be easily recyclable - check local facilities. The sticky labels and any bubble wrap are unfortunately not recyclable or biodegradable and should be placed in the general rubbish bin. All our newspapers, brown paper, and bubble wrap are sourced second hand to help reduce waste.

Any plant pots that are square and black are not recyclable and should be re-used or placed in the general rubbish bin. (We do not buy these pots any more but we will continue to wash and re-use them until they are all gone). Any plant pots that are round and grey are recyclable and should be re-used or washed and placed in household plastic recycling.

We don't like using polythene bags for the plants and would prefer to use biodegradable plastic bags instead. However, because our plants are very wet, biodegradable materials rapidly disintegrate - before the order arrives with the customer - when we have tried them. We have considered using oxo-degradable plastic bags but environmental groups consider these to be worse than standard plastic bags. Hopefully in the future a better alternative will come along. Our plastic bags are sealed by us and cut to size, to minimise plastic wastage. We welcome suggestions on how to make the packaging more environmentally friendly. 

About our plants

Where do your plants come from?

100% of the plants we sell are propagated directly by us from our own stocks here at the nursery in Norfolk. All are raised from seeds or cuttings/divisions. We do not buy in plants and sell them on, because it cannot be guaranteed that these will be true to name. (In recent years, with the advent of large numbers of foreign-grown plants, this has become a big problem in the aquatic industry). All our plants are thus British-grown specimens, so they are already adapted to our climate when you receive them.

How large are your plants?

We supply young but established plants in pots; we do not sell plugs. To give an idea, they are approximately the size of the smaller potted plants that you would buy in a garden centre. The average plant we sell is about about one year old (fast-growing plants are around six months old when we sell them, and slow-growing plants around two years old).

I asked to be told when a plant was back in stock. I can see it's in stock but I haven't been notified?

Because we produce all our plants from scratch ourselves, they are often available in limited quantities. If we have more people on the list to be notified than we have plants available, we will contact some of the people on the list but not all, starting with those that asked first. After giving them some time to purchase, we will then continue contacting the people in turn until the plants have sold out. This helps avoid people being told that a plant is back in stock and that they can buy it, and then finding that they can't.  

Alternatively, we may have tried to notify you but your spam filter may have rejected the email. 

Do you use any pesticides?

No, we do not use any chemical pesticides or sprays on our plants. Large pests, such as snails and caterpillars, are hand picked, and small pests, such as beetles and aphids, are rinsed off with water. We also use natural (biological) controls, e.g. purchasing native ladybirds from specialist suppliers and releasing them on plants affected by aphids.

General plant care questions

How many plants do I need for my pond?

For a pleasing look, aim to have one-third to two-thirds of the water surface covered by oxygenating plants and plants with floating leaves such as waterlilies, and the rest clear. Aim to have marginal plants around one-third to two-thirds of the pond edge, and the rest open. This rule is also optimum for keeping fish, which do not like either completely bare ponds, or completely covered ponds. 

Pick the plants you would like, then work out how many feet of water surface or of pond edge you want to cover. On each plant's page on our website, we suggest an approximate planting density. This density should give you a nice look for that area in two to three years. From this you can work out how many of each plant you would need. (Please remember that planting densities are just a guide, and growth rates will vary depending on how sunny or deep your pond is, what soil you use, where you are in the UK, what varieties of plant you choose, and especially on the size of pot you use). For most people, budget will be the main limiting factor in how many plants they buy when setting up their pond. Don't forget to allow in the budget for any pots or soil that you might need. 

How do I choose what plants to have?

Consider choosing plants that give different colour flowers and/or flowers at different times of the year (Marsh Marigolds for yellow flowers in spring, Loosestrife for pink flowers in early summer, Pickerel Plant for blue flowers in late summer etc). Foliage is also important – try to choose one or two things that are evergreen, such as Japanese Rush, or Horsetail, so that the pond has some winter interest. For a balanced look, choose both tall slender plants and low bushy plants. If you are trying to hide the edge of the pond, choose plants with creeping stems and a scrambling habit, such as Water SpeedwellMarsh Pennywort, or Water Mint. These grow in wet soil and shallow water and also 'raft' out onto the surface of deeper water, covering it. They can also be used as underplanting (planted around the base of taller plants) to hide the edges of pots (but do thin them out if they begin to swamp the taller plant). Plant heights, flower colour and flowering times are all given on this website on each plant's page.

Around the edge of the pond, aim to have a mix of taller and shorter marginal plants. Don't space plants evenly around the edge, as this won't look natural - plant in clumps. For larger ponds, you can buy several of the same plant and place together in one larger pot.

If you want to use plants to encourage wildlife, the single most important thing is to choose plants from each category so that you have a range of habitats within the pond - plants with underwater foliage, such as oxygenating plants, plants with floating leaves, and marginal plants around the edge. It is also helpful to emphasise British native plants, as they are overall more likely to be useful to our local wildlife. If you specifically want to encourage dragonflies and damselflies, make sure you have some marginal plants with tall stems that the larvae can crawl up as they emerge from the pond before flying away. If you are interested in butterflies and bees, try to choose plants that are on the RHS 'Perfect For Pollinators' list, such as Loosestrife or Water Forget-Me-Not. For frogs, toads, small mammals, and birds, try to place some of your marginal plants and marsh plants around the pond’s edge in such a way that it blends with the vegetation of rest of the garden, to give cover so that small animals can enter or leave the pond without coming out into the open.

The majority of pond plants like a position that is sunny to partial shade. If you plant them in deeper shade, they will usually survive but will not flower well or at all. If you have an area of deeper shade, consider non-flowering plants such as grasses or ferns like Japanese Rush, or Horsetail. Creeping plants such as Marsh PennywortWater Speedwell, and Water Mint, will produce nice-looking foliage in shade even if they don't flower. Oxygenating plants will also grow in shade, albeit more slowly.  

When is the best time to add plants to my pond?

You can plant up your pond at any time of the year. The optimum time for most potted pond plants is late winter/early spring, as this means that they go in their new pots with fresh soil and food just before they start to grow, so they get the most benefit from this. However, this is preferable, not essential, and it also depends on what qualities you have chosen the plant for. For example, if you have chosen a plant which flowers in very early spring, it may be better to get it planted up and established the previous autumn so that it is not moved and trimmed while the flowers are forming. Or if you are planting a natural pond with a soil bottom, it will be pleasanter to plant, and the plants will establish faster, if you plant in late summer or early autumn when the soil and water are warm.

Floating plants are not usually available in the winter as they disappear down to small buds or shoots on the bottom of the pond and we don't sell them as we think people might be disappointed with how they look. If you want these plants, you will usually have to buy them between April and September.

With the exception of frost-tender plants (which we protect under deep water or in an unheated polytunnel until the last frost) all of our plants are used to living outside in the British climate. They can all be put into your pond at any time of the year. This includes the frost-tender ones, provided that you adhere to the planting depth on the label. 

How do I choose soil and pots for my pond plants?

When potting a pond plant, you can use normal plastic garden pots (those with solid sides and the holes in the bottom) like any other potted plant if you wish. These have the advantage of being low cost and easily available. However, if possible, opt for open-mesh aquatic baskets; these allow the plant’s roots to escape the pot and spread out into the pond water. Plants generally grow better in them because they are less confined, and will last longer before needing re-potting (although they will be more difficult to re-pot when the time comes, since the roots will be harder to disentangle from the pot).

Most modern open-mesh aquatic baskets have quite fine mesh and do not usually require a hessian liner to hold the soil in, but if you are using very fine powdery or sandy soil, have a basket with a very open mesh, or have a significant water flow, you may still need a liner. Newspaper will do as a liner if you have nothing else, but bear in mind that it is not long-lasting in the way that hessian liners are and may disintegrate if the pot is disturbed later. An alternative to pots is to use aquatic planting bags – these are flexible, permeable, mesh bags which will not leach soil out and which can be fitted into awkward places. 

Do ensure that whatever pot you choose gives your plants enough room. Many aquatic plants, and waterlilies in particular, need the space for a large root area. Do not place these in small or cramped pots if you want them to perform and flower well. Small marginal plants, oxygenators, and miniature waterlilies can be started in pots of around 1 litre capacity, while larger marginal plants and other waterlilies are best started in pots of 2 to 5 litre capacity. We generally recommend that each variety of plant is potted individually, so that they are not competing for space in one pot. You can find more specific information on each plant's page on our website.

Pot the plant in a heavy, loamy soil. This is a soil which is composed of sand, silt and clay, rather than being a peat-based soil (which will tend to float and is not nourishing enough for water plants in the long term). Soils like this will usually look brown rather than black. If you are potting waterlilies or deep-water plants such as Orontiums, these like an even heavier soil, such as a heavy clay with around 30% clay content. Special aquatic soil is available in most garden centres and this is a good compromise for all pond plants. Alternatively, normal garden soil from somewhere like a flowerbed, that has been raked or sieved to make it workable, can be used. Do not use standard potting compost or any garden soil that has recently been fertilised, as this can cause excessive algae and/or green water in the pond.

When growing pond plants in pots, for best results we would advise that they are re-potted or divided every two years, or at least every three years. This is especially true for waterlilies and water irises. We would also advise that waterlilies are fertilised once a year, ideally in spring, if you are not re-potting them that year. It is best to use special aquatic plant fertiliser, as standard plant fertilisers can dissolve and leach out into pond water. You can fertilise a plant without re-potting it, if you don't mind getting dirty hands, by pushing a slow-release fertiliser tablet down into the soil until it is around the plant's roots. 

What if I don't want to pot my plant but want to put it directly into the ground?

If you are planting a bog garden, if you have put soil on the base of your pond, or if you are lucky enough to have a natural pond, you can simply plant your plant straight into the ground as you would any garden plant. Most pond plants appreciate plenty of room for their roots, and will grow well when planted out like this. In this case, if the area is above water, prepare the soil by digging it over and removing any weeds that might compete with your plants. If the area is under water, clear away any weeds, leaves or other debris, but there is no need to dig the soil over. Then simply use a spade or trowel to dig a hole where you want the plant to grow, deep enough and wide enough to comfortably accommodate the whole of the roots. Place the plant in this hole; if it is a bare-root plant, spread its roots out with your hand. Hold the plant around its root ball or, for bare-root plants, at the base of the growing point (the growing point is the bit where the shoots and leaves emerge, also called the crown) and carefully fill the hole with soil, firming it up as you go. Make sure the plant’s growing point is just above the soil level when you have finished. Gently firm the last of the soil back down with your hand or the heel of your foot. If your natural soil is very poor, consider filling the hole back in with shop-bought aquatic soil rather than your own soil – this gives the plant a pocket of better soil to help it establish.

Occasionally, you may want to grow plants directly in the ground in an area under water too deep, or too far from the bank, to easily dig a hole. In this case, you can place the plant in a ‘bag’ made from a square of hessian, together with some soil if necessary, and a few medium-sized stones as a weight. Draw together the ends of the hessian to create the ‘bag’ and tie them loosely with biodegradable string so that the stems of the crown are emerging from the top. Drop the bag into the water where you want the plant to be, making sure it will not be too deep for the plant to thrive. Keep an eye out to ensure the plants are not disturbed by fish or water birds while they gradually root into the pond.

The label included with the plant will specify a minimum and maximum water depth; the plant will grow best at the shallowest end of this range, as it will get the most light. Similarly, remember that most flowering pond plants will flower best when placed in a sunny spot.

If the weather is hot when the plant is first planted up and it begins to wilt, simply trim the wilting foliage back. This will not harm the plant.

Which pond plants are suitable for shade?

The majority of pond plants like a position that is sunny to partial shade. If you plant them in shade, they will usually survive but will not flower well or at all.

If you have an area of shade, consider non-flowering plants such as grasses or ferns like Japanese Rush, Corkscrew Rush, or Water Horsetail - they will tolerate fairly deep shade and their evergreen foliage actually looks better when grown in a sheltered location. Ivy-Leaved Duckweed is a floating plant which does extremely well even in deep shade, and in this situation will look fresher and cleaner than it does in sun. Creeping plants such as Marsh PennywortWater Speedwell, and Water Mint, will generally produce nice-looking foliage in shade even if they don't flower. Oxygenating plants will also grow in shade, albeit more slowly. If your shade is due to tree cover and is absent in the spring, Marsh Marigolds, a spring-flowering plant, are a good choice. Apart from these, it may simply be a case of experimenting until you find what works in your location.

Plants to avoid if you have a shady pond would be waterlilies (consider Water Hawthorns instead), water irises (unless you don't mind their not flowering), and cottongrasses.

Are there any plants that are suitable for ponds with ducks?

Unfortunately ducks are one of the worst things when it comes to pond plants, because they physically dig and uproot vegetation. If you are planting a pond visited by ducks, we would suggest trying larger marginal plants, placed around the edge of the water. Examples would be the native iris species, Iris pseudacorus and its cultivars such as the variegated or double types, Iris pseudacorus 'Variegata' and Iris pseudacorus 'Flore Pleno'. Also things with tough fibrous leaves or stems such as Sweet Galingale (Cyperus longus), Golden Sedge (Carex elata 'Aurea'), native Horsetail, Equisetum hyemale, and purple loosestrife, Lythrum salicaria

You can try adding softer plants and underwater plants such as oxygenators, because every situation is different and animals are unpredictable. However, be aware that it is a gamble and that there is a good chance of loosing these to the ducks at some point, so perhaps don't spend too much money on them.

Whichever plants you choose, we would suggest putting chicken wire or something similar around them when they are small and new, in order to enable them to get established. 


Can I have pond plants in with my koi?

Due to their large size and love of rooting about in the soil, it is not usually possible to have pond plants in with koi. But if you have a koi pond and do want to see plants, there are a number of ways to get around this.

Firstly, you can simply have an area of the pond that the koi don't have access to. This can be by creating very shallow shelves, too shallow for adult koi to swim in, or having a smaller pond linked to the koi pond, perhaps as a header pool. (An extension of this idea is the vegetable filter, where the flow of water from the pond pump is diverted through a container of pond plants before returning to the pond). Finally you can simply use nylon mesh just under the water surface to segregate an area and deny the koi access to it (but be aware that koi jump and will need to be retrieved from this area from time to time). 

Secondly, you can try floating plant islands. These are available from large aquatic shops or online, round or square, in different sizes, and can also be linked together. They are essentially aquatic planting bags held up by an integral ring of polystyrene. (You can also get custom-made ones if money is no issue). They are planted with aquatic soil and then almost any marginal plant that you wish. The islands are quite heavy but if you have strong circulating pumps, you might need to ensure they don't drift around the pond by attaching them to the sides with twine etc. Consider planting with something tall like an iris and then underplanting with something scrambling like water speedwell, watercress, or marsh pennywort, so that the scrambling plant will hide the edges of the island and eventually make it look like natural plant growth. (Although scrambling plants grow fast - if you think you will never thin them out and they'll swamp the tall plant, perhaps best just to stick with the tall plant). 

Finally, you can try large/tough plants that the koi are less likely to eat. Waterlilies are the most popular choice, as they are attractive and can grow at the depths found in many koi ponds. Choose a large lily (advertised leaf spread of at least 100cm) and ensure its soil is well topped with gravel. You can also try tough, fibrous plants; the same strategy as is used with waterfowl. The difficulty with these is the depth of the average koi pond - try carefully building stable plinths composed of things like house bricks, which are chemically inert - don't use concrete blocks. Suitable plants to try would be things like Cyperus longus (Sweet Galingale), Carex riparia (Greater Pond Sedge), and Typha latifolia (bulrushes, including variegated versions). It must be said though that adding waterliies or tough, reedy plants works much of the time, but certainly not all the time. Like all animals, koi are unpredictable and you will not really know until you try. It is sometimes said that you can distract koi from eating the pond plants by offering regular feeds of fresh lettuce, orange slices etc, but in our experience this doesn't seem to affect it one way or the other. 

Which British native plants would you recommend for a wildlife pond?

To encourage wildlife, we would suggest choosing plants of each type so that you have a range of habitats within the pond - plants with underwater foliage, such as oxygenating plants, plants with floating leaves, and marginal plants around the edge with emergent stems for the larvae of flying insects to crawl up. 

All of the oxygenating plants that we do are British natives and would be suitable. Mixing different species will give a slightly wider range of habitats, although unless your pond is large it will look less natural than having all the same species (in the wild, plants don't tend to grow in small numbers of lots of different types, but in large clumps of the same type). If you only go for one type, we would suggest avoiding Hornwort or Crowfoot, since each of these dies away at certain times of the year and would leave you for a period without any oxygenating plants (Hornwort dies away in winter and Crowfoot in summer). 

For floating-leaved plants, Floating Heart is a very easy one to grow and has the advantage of giving you cover fairly quickly, although in small ponds it might need to be cut back by the end of the season. 

With regard to marginal plants, Loosestrife is very popular indeed with bees and butterflies, as is Marsh Cinquefoil and to a lesser extent Water Forget-Me-Not. Creeping plants such as Water SpeedwellMarsh Pennywort and Water Mint are useful to scramble around the edges of pots or the container and help to hide them. The flowers of Water Mint especially appear later in the year when other plants are done and are loved by bumblebees. 

Finally, try to 'blend' the edges of the pond into the rest of the garden with vegetation so that small animals can enter and leave it sheltered and unobserved. Try to plan shallow areas or escape routes for any wildife that might get trapped in the water - animals such as rodents can climb up, fall in and drown even in free-standing ponds. 

How do I hide the edge of my pond, or the edges of my pots?

Sometimes, parts of the pond liner or concrete edging can be visible around the edge of the pond. This may be part of the design in formal ponds, but can look out of place in ponds intended to appear natural. In natural ponds and streams, the vegetation usually continues right into the water, changing from terrestrial plants to water-loving ones as the soil gets wetter. If you need to hide the edge, try adding low-growing, scrambling plants such as Water SpeedwellMarsh Pennywort, or Water Mint. These grow in wet soil and shallow water and also 'raft' out onto the surface of deeper water, covering it. They can also be used as underplanting (planted around the base of taller plants) to hide the edges of pots (but do thin them out if they begin to swamp the taller plant). 


My pond has gone green - is this normal?

It is completely normal for new ponds to go green. In fact, they are much more likely to go green than not. Every year we are contacted by people who have recently built a new pond and put in some plants, and are puzzled and worried because, about two weeks later, the water has gone very green, and/or slimy green strands have appeared everywhere. It's important to remember that the majority of ponds you see, either in the wild or in people's gardens, have been established for a while, and have gone through this stage. Green water - the 'pea soup' effect - is caused by single-celled or tiny individual algae suspended in it, while blanketweed, stringy algae, or slimy algae, are caused by filamentous algae. Filamentous algae is usually attached to surfaces, such as the pond sides or plant leaves, but it may be free-floating. 

You cannot keep algae out of your pond by anything that you do, and you do not 'catch' it from anywhere as such. Another common thing that people say to us is, that they bought plants from another nursery and 'caught' algae from them. This widespread belief is one reason that we carefully wash and clean all our plants before they go out so that they have no algae on them, but in truth it makes no practical difference. What has happened in this case it that the person has built a new pond, or cleaned out an old one, and then bought plants from a less careful nursery, which arrived with visible algae on them. When their pond goes green, or filamentous algae appears, soon afterwards, they naturally assume this has come in with the plants. In fact any body of water that is new, or disturbed in some way, will inevitably go green, and the timing is coincidence. The algae is triggered by nutrients being released into the water column - nutrients either from the tapwater used to fill the pond or from adding plants in pots of soil. More rarely, nutrients are released from disturbing sludge on the bottom when cleaning. Algal cells can indeed come in on plants, but this is true even if the plants appear completely clean, and they can also come in on the wind, on birds' feet, on aquatic insects, etc. Algae cannot be kept out, except by the constant use of strong disinfectants in the water, as is done with swimming pools. 

However, algae is mostly harmless. (If you are interested in wildlife it's also helpful to remember that it is natural, and is the primary basis for the aquatic food chain). Gardeners strongly dislike the appearance of algae and green water, and often think they have to quickly remove it in some way. Very intense growths of algae can indeed cause some water quality problems (mostly low oxygen levels or pH swings) which can harm pet fish, but these are not common and can usually be avoided by circulating the water with a pump. If you don't have fish in your pond, then algae is more of a cosmetic issue. The most likely problem it can cause is that it may cut out light to your deep-water plants, and delay their establishing. It isn't likely to kill them, but if it is very extreme and prolonged and the plant is small and vulnerable, there is a small chance of this. If your plants seem to be really struggling for light, green water problems can be avoided by raising the plant higher in the water so that light can better penetrate to it. Stringy algae problems can be avoided by physically pulling it off the plants as much as you practically can. There are also numerous over-the-counter algae treatments you can buy from aquatic shops, from barley straw to phosphate blockers - these are generally harmless to plants and aquatic life and work well provided that they are regularly re-applied.

Algae will in fact usually go by itself. Or rather, it will settle down to a naturally low level that most people are happy with. Once a pond has been set up for a while, the nutrients tend to leave the water column and become incorporated into the substrate and the plant material, and the pond clears. Invertebrates that feed on algae start to move into the pond and it falls to the bottom in their droppings, or it simply exhausts the food supply and dies back. In a pond without any plants at all, it will persist but at a lower level. In a pond with a good amount of plants, once these are established they compete with the algae for light and nutrients, and keep it under control. Provided that there isn't a continual influx of new nutrients into the pond (from ground run-off, fish being fed, waterfowl droppings, or dredging of sludge) it should then stay clear. It's common for an algal bloom to appear in spring each year - algae's ecological niche is to get going in spring quicker than the plants can - but this clears as the year advances and the plants catch up. Algae may bloom again in an established pond after a disturbance, such as adding new plants or cleaning the pond, but this bloom is usually much shorter lived than the initial one. 

If you do have a continual flow of nutrients into the pond, from fish that you are feeding every day, from waterfowl, or from ground run-off, you can fight the algae by choosing faster-growing plants that will compete better with it. It will also help if you thin their excess growth regularly and remove it. When you remove plant foliage from the pond and compost it, you are also removing the nutrients locked up in its structure (rather than leaving it to die off and re-release these nutrients back into the water). If this is not enough and algae is still a problem, speak to your aquatic shop about ultra-violet units, phosphate blockers and biological treatments.