Choosing Pots, Soil and Fertilisers For Your Pond Plant
Pots: Pond plants are traditionally potted in open-mesh aquatic baskets, and we would recommend that you use these if you can. These allow the plant's roots to escape the pot and spread right out into the pond water. Plants generally grow much better in them because they are less confined, and will last longer before needing re-potting. If you can't find or afford aquatic baskets, you can use normal plastic garden pots (those with solid sides and the holes in the bottom) like any other potted plant. These have the advantage of being low cost, readily available, and easier to remove when the time comes to re-pot (it is often difficult to disentangle plant roots from the mesh of an aquatic basket). However, because solid pots do strongly restrict the plant's roots, make sure that you re-pot the plant at least once a year.
Do ensure that whatever pot you choose gives your plant enough room. Most aquatic plants like a large space to spread their roots out (more than garden plants do), and will not perform or flower well in small or cramped pots. 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. You can find specific information on recommended pot size on each plant's page on our website. For best results we would advise that they are then re-potted or divided every two years, or at least every three years.
We generally recommend that each variety of plant is potted individually, so that they are not competing for space in one basket - they will never grow at exactly the same rate. If you do want to do a mixed pot, check it at least once or twice in the growing season to see how the plants are getting on together and if one is starving or smothering another.
Liners: Modern open-mesh aquatic baskets have fine mesh and do not usually require a hessian liner to hold the soil in. If you firm the soil down well and place the pot in the pond carefully, the soil will generally stay in place. However, if you are using fine powdery or sandy soil, have disturbance from fish or from flowing water, or are using an old-fashioned large-mesh basket, it would probably be a good idea to use a liner. Paper 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 will disintegrate if the pot is disturbed later. If using solid garden pots, it's best to line the large drainage holes at the bottom with paper.
An alternative to pots and liners is to use aquatic planting bags or planting socks – these are flexible, permeable, fine-mesh bags, generally made out of woven plastic, which will not leach soil out and which can be fitted into awkward, uneven, or shallow places and rolled down to reduce size. They do restrict roots but less than solid pots do, because of their permeability. Another alternative is to shape your own planting bags out of hessian squares. These are fully bio-degradable, but this also means that they will eventually disintegrate in the pond, probably before the plant needs re-potting. Finally, for ponds without shelves you can buy overhanging mats - mats of woven plastic or hessian which are pegged to the bank of the pond and hang down into it. Marginal plants, with soil, are placed in pockets in the mat.
Soil: 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). Loamy 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 soil (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.
Fertiliser: It is best to use special slow-release aquatic plant fertiliser, as standard plant fertilisers will quickly dissolve and leach out into pond water. There are no hard-and-fast rules about fertilising pond plants, as it depends on the type of plant and on the soil used. As a guide, if potting a plant in fresh shop-bought aquatic soil and a nice large pot, it will not usually need added fertiliser. If potting it in poor, sandy soil or a pot that's on the small side, consider adding fertiliser, especially if it is a heavy-feeding plant such as a waterlily.
If you do not intend to re-pot the plant that year and it is a heavy-feeding plant such as a waterlily, we would advise that you fertilise it once, ideally in spring. 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.