Pond Plants 101
Choosing plants for your pond or water feature isn’t as complicated as it seems!
PLANTING ZONES To make it easy to work out where particular plants should be planted, water plants are labelled and categorised by the ‘zone’ or areas they prefer to grow in. If you imagine a side-view of a lakeside or river bank where pond plants evolved in the wild, you will notice that the soil conditions will get wetter the closer to the water you go. Plants growing in a marshy meadow or along the river bank will be in slightly-soggy soil conditions. These are commonly called ‘bog plants’ or ‘moisture-loving plants’. Plants from the river bank right next to the water (or in the water margins) would be in much wetter soil and these are called ‘marginal plants’. Bear in mind that through the year (and even day-to-day) the weather conditions change, so most plants are very capable of coping with a change from their official recommended zone – two weeks of rain or a month of drought can cause a river bank to flood or run dry, and those normally boggy banks can become completely submerged or totally dry out—usually the plants just take it in their stride and after a period of adjustment (e.g. shedding a few of the leaves) will adapt to the different conditions. Don’t get too hung up on measuring water depth with a tape measure and poring over every plant label—all the plants we sell would be happy if the water level was where the pebbles on the top of the pot are, so if you want to keep things simple you can just plant all your bog and marginal pond plants at this depth!
ZONE 1 These are called ‘bog plants’ and ‘moisture-loving plants’ and basically need damp roots but dry leaves. They are ideal for planting in shallow containers or areas with no drainage where the soil is always wet, but can usually also go on the shallow shelves of the pond so long as the water doesn’t cover the top of the pot.
ZONE 2 These are the ‘shallow marginal plants’ which can go on the first shelf, usually in water up to 15cm deep. As a general rule they prefer “wet roots and dry leaves” like the bog plants so you may need to jack them up on a brick to keep them at the optimum height.
ZONE 3 These are plants that like to be submerged up to about 30-45cm under the water, such as ‘pygmy lilies’, some ‘deep marginals’ and the ‘oxygenating plants’.
ZONE 4 This is where the larger water lilies thrive, growing from pots at the bottom but sending leaves up to float on the surface and shade the pond.
ZONE 5 Floating plants have leaves above the surface but roots dangling loose so they provide shade and remove excess nutrients from the water, which helps to combat algae.
CHOOSING PLANTS Try to build up your plant selection throughout the growing season so you get a rolling display of plants in their prime all year. Choose a good mix of plants for the different zones/water depths. As a rough guide, position marginal plants on the shelves in groups; usually odd numbers in random positions look best in a natural/irregular shaped pond and even numbers of plants arranged symmetrically look best in formal rectangular or circular ponds. Generally, a sparsely-planted pond with the odd plant here or there looks underwhelming and unfinished: the more plants you have, the more natural your pond will look and the more wildlife you will attract. Make sure you have plenty of oxygenating plants (10 bunches m2 of surface area) to compete with algae. All plants produce oxygen, but remember that they are only adding oxygen to your water if their leaves are underwater, otherwise they are just oxygenating the air! They will only help keep your pond clean if the roots are loose and taking nutrients out of the water—if they’re in a pot of compost they will cheat and get their nutrients from the compost! Choose floating plants and lilies for surface cover to limit the amount of sunlight that can cause algae growth. Some marginal plants spread their leaves and roots over the water surface, which is ideal if you’re short on space and need a plant to do three jobs in one! Aim for 70-80% of the pond area to be planted to ensure a natural balance.
CHANGING CONDITIONS Water plants generally cope very well with changes in growing conditions but you may need to forgive them a period of adjustment or “sulking”. If/when you move them. Leaves are a different texture and colour depending on whether they are grown above (emerse) or below the water (submerse). If you move a plant during its growing phase, the plant may need to shed any leaves that have changed condition and re-grow leaves better suited to the new conditions. This means leaves that have grown out of water for CO2/O2 exchange in the air can’t suddenly switch to being underwater just because you’ve plonked them on a deeper shelf: the plant would need to shed the emerse leaves and grow new submerse leaves to respire and photosynthesise underwater. While it’s making these adjustments, prune off any leaves that are starting to look yellow or brown and give it a few weeks to regenerate—it won’t disappoint you!
WINTER CARE Like many plants in the garden, some pond plants die back in autumn and winter. This is a natural phase of a plant’s lifecycle to give it time to recharge for next summer’s growth and reproduction. Winter conditions are particularly challenging for water plants as ice would damage leaves/stems, so most water plants have evolved to be dormant in winter. This means that in autumn the leaves will start to wither and fall off, and you’ll need to prune off any dead leaves to stop them decomposing in the pond.
PRUNING Through the growing season, plants may need trimming back if they are growing in the wrong shape and to encourage new growth. In general, treat them as you would other garden plants and don’t do anything too drastic during the growing season. It is normal for plants to shed a few leaves through the year, usually from lower down the stems. New fresh growth appears at the tips or from the centre of the plant, and older growth at the bottom or round the edge dies off. This is how the plant focuses its energy on new growth, just as pets constantly shed hair but don’t end up bald (hopefully)!
REPOTTING and FERTILISING Like any other plant in the garden, pond plants need ‘food’ to grow. They get this in the form of nutrients which they absorb through their roots in the case of potted marginal plants, and also through their leaves in the case of plants that have their leaves underwater. This means that you will sometimes need to renew the compost of potted plants and split/divide any plants that are pot-bound (where the roots are bursting out of the pot). This is best done in early spring so the plants are all-set with the nutrients and space they need to thrive in the year ahead. If repotting isn’t an option you can poke fertiliser tablets down into the pots, and use liquid fertiliser to add to the water to boost plants with their roots loose in the water (like the oxygenators and floating plants). Make sure you use a specialist aquatic fertiliser that is safe for wildlife and doesn’t cause algae. We offer a ‘splitting and repotting’ service—ask us if you need help.
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