Method to divide and repot a waterlily:
A waterlily can be split and repotted when it is actively growing ideally Spring:
1. Use hard rhizome only - discard soft and mushy portions.
Cut the rhizome so that each piece has a growing tip and thin white feeding roots to stimulate new growth.
Cut back the long white anchor roots to 6" at the rhizome.
Trim away any damaged or dead leaves on long stems but leave the young or unfurled ones close to the rhizome.
2. Fill a mesh basket about two-thirds full of aquatic soil or clay garden soil. Wet soil works best.
Make a mound in the middle of the pot with a handful of soil.
3. Push an XL feed ball into the soil.
4. Place the rhizome on the mound and spread the roots out over the top of the soil so they are not under the rhizome in a squashed lump.
5. Add soil to cover the roots and around the rhizome. Do not bury the rhizome.
The point of the crown should have no soil on it or it will have difficulty sprouting new leaves.
6. Water the pot thoroughly. Keep the new waterlily plants at the shallow end of the pond with no more than 4-6" of water over the basket top until new growth appears. You should see new growth in 7-10 days depending on the month you replant.
7. By May-June the waterlily should be lowered to about half its final depth and it should stay there for the rest of the season.
Hardy water lilies are considered perennial aquatic plants and will survive the winter provided the rhizome does not freeze so they should have at least 6" of water over the top of the basket by the end of Autumn.
Waterlilies thrive by sending out root growth to surf the water for nutrients. Their root spread is often as large as their surface spread - this is not wrong and a successful waterlily will need this root expanse to thrive.
Alternatively if you cannot lift the waterlily out of the water you can deal with excessive growth in situ (see below).
Pruning a waterlily in the pond:
If your waterlily is too large and has become too heavy with roots that stretch out across the pond base then do not give yourself a hernia by trying to lift it out to repot it.
Instead, prune the crown of the plant in the same way that you would a shrub in the garden.
1. The display of rhizomes (or branches in the case of a shrub) should be evenly spaced around the crown and each should be heading in a different direction.
2. If the plant rhizomes are congested - cut out 1 in 3 of the close rhizomes with a sharp knife to allow each to have its own space. If they are crossing then remove the weakest and allow just one to continue.
3. When you have finished, the network of waterlily rhizomes should look like the open branches of a newly pruned shrub.
4. You can trim back the pieces of rhizome you have just removed and repot for future use. See 'How to repot a waterlily' above.