How to perfectly re-pot pond plants
Spring is a great time to sort out your pond plants. Dead looking brown leaves are being replaced with strong green shoots and the plants are identifiable again and of use to the pond decoratively and biologically.
But to get the best out of pond plants should be trimmed, split, space out and repotted. Repotting is especially important for newly purchased pond plants as those small pots aren’t intended as forever homes.
Marginal pond plants typically come in 9cm, 11cm (1 litre,) or 2.5 litre pots. At these sizes the plants are of course young plants, fresh out of the nurseries, and not necessarily best equipped for a life on the average garden fish pond. What they need instead is a large pot to accommodate lots of root growth, a nutritious, pond water-friendly compost, and some protection from fish.
First, you’ll need planting baskets. The average marginal pond plant will need at least a 22-23cm planting basket, available either in round or square shape. If you can accommodate larger then do so, and contour shaped baskets are large yet slim enough to still sit on a marginal shelf. And for water lilies, a 40cm basket is better still.
Note that aquatic planting baskets are different to standard garden plant pots as they are full of holes to allow the flow of water through the pots, enabling oxygen around the roots and the roots access to the pond water all around them. Ponds plants take up nutrients through their roots so the more access they have to the pond water, the better. Pond plants can even help prevent algae by taking up nutrients from the water.
Pond too deep? Floating plant baskets are available
Hessian has long been used in water gardening to hold the aquatic compost around the plant and prevent it from spilling into the water. The ideal is to line the planting basket with one or two sheets of hessian, keeping the dirt in, while allowing plant roots to grow through it long term. It also won’t affect the water.
Aquatic compost is not just any compost. It has lower nutrient values than standard garden compost (which would fuel nuisance algae growth if used,) and is pH neutral, whereas many standard garden composts also contain lime, which could raise water pH to dangerous levels.
Gravel and stones are essential to be placed on top of the baskets to keep the soil in and fish out. Large fish, especially Koi, will dig and grub around in planting baskets looking for food.
Its common for unprotected marginal and deepwater plants to have all the soil dug out by fish which then leaves the delicate plant roots exposed, soil on the bottom of the pond, clogging filters, as well as removing that all-important nutrient source for the plant. So place a deep layer of coarse gravel over the top of the pot before lowering it into the water.
You’ll also need scissors or a knife to cut away the spare hessian around the top of the pot, and to cut leaves and roots. Lets get started!
How to re-pot, step-by-step
- Remove the plant from the old pot. Newly purchased plants should come straight out, and established plants may need cutting out of old pots, Don’t be afraid to cut through the roots.
- Give the roots a trim, so that they fit vertically inside the new pot without having to be laid around the inside or doubled back. Trimming the roots will encourage new root growth, so don’t be afraid.
- Place hessian inside the new planting basket, covering all the holes in the side and base
- Put a layer of aquatic compost in the new basket
- Place the plant in the centre of the pot, holding it upright with one hand.
- Fill the pot to the top with aquatic compost, using the other hand.
- Push the soil down firmly around the plant so that it stands up centrally, of its own accord.
- Place a one to two-inch layer of coarse gravel over the top of the pot, up to the rim.
- Trim the overlapping hessian for a neat job
- Place the newly potted plant slowly and carefully in the pond.
Some plants like Flag iris and water lilies can get very large over time, creating a root mass several feet across. These can be divided with a sharp spade or large knife into several smaller plants and repotted in the same way. Cut vertically through the root mass, ensuring that each segment has sufficient roots or rhizome in order to continue to root and grow in the normal way.
Feed your plants
One aspect that’s often overlooked with pond plants is fertilisation. Just like any plant if you want the best from your plants, or if they look like they are struggling, give them a feed.
Available in liquid or tablet form, feed your pond plants with pond specific fertiliser and they grow greener, lush foliage and flower much better. Water lilies are particularly hungry feeders so if you haven’t repotted or fed them for several years, some fertiliser will go a long way to improving their health.