Advice
RHS Help & Advice
Waterlilies
Waterlilies are probably the most popular and easily recognised aquatic plant. They can also be grown in just about anything - from a lined half wooden barrel to large specialist water gardens/lakes.
To grow successfully they require calm, still water away from disturbance by waterfalls, fountains or pumps and a sunny position.
When buying a plant check that the crown looks healthy and check for damage to leaves or buds. Ensure the nursery or garden centre display area is not full of weed as you could inadvertently introduce other problems to your pond.
Look at the label for the ultimate size, making sure the plant grows to a suitable size for the water feature you have and that the feature has enough depth of water. These plants vary widely in their vigour, so it is important to choose one that will not grow too large. Smaller cultivars can be accommodated in large ponds by using bricks to raise up and support the plant, effectively making the water shallower, but the most vigorous kinds will take over smaller ponds.
Choosing
Vigorous lilies
The largest waterlilies can be grown in ponds 75cm-1.2m (2.5-4ft) deep. Try free-flowering Nymphaea ‘Escarboucle’, which is red, or ‘Gladstoneana’, with star-like, white blooms. The pads of these will cover a circle at the surface 1.2-2.5m (4-8ft) across.
Ponds with a water depth between 45-75cm (18-30in) are ideal for fully double white ‘Gonnère’ and deep red ‘James Brydon’. Both can cover 90-120cm (3-4ft) at the surface. Primrose yellow ‘Marliacea Chromatella’ tolerates the same depth of water but requires slightly more room at 1.2-1.5m (4-5ft) across.
Smaller cultivars
Shallower water between 30-45cm (12-18in) deep is suitable for creamy-apricot ‘Aurora’ (left) and early, free-flowering red ‘Laydekeri Fulgens’, the colour of which intensifies as the blooms age.
The smallest ponds, such as half barrels, can still provide enough room for ‘Pygmaea Helvola’ (right), yellow flowered with tiny marbled leaves, or white N. tetragona.
Planting
Waterlilies are best grown in plastic planting baskets. Choose one of a suitable size for the plant’s vigour, line with hessian and fill with ordinary garden soil or aquatic plant compost, planting the crown at soil level.
Submerge lilies so that 15-25cm (6-10in) of water covers the crown. For smaller rhizomes (5-10cm/2-4in in length), reduce the depth to around 8cm (3in); larger rhizomes (10-15cm/4-6in in length) to about 50cm (20in). To ensure you get the correct depth place the containers on bricks or other raised platform or, more drastically, temporarily reduce the level of the pond while the plants establish. If in doubt plant shallowly.
Once the plant becomes established gradually increase the depth above the crowns to twice the original planting depth.
Feeding
Waterlilies are hungry plants. Feed with a proprietary aquatic slow-release fertiliser following the manufacturer’s instructions and placed in the vicinity of the root system. Remove any yellow leaves.
Dividing
Waterlilies can be divided about every four to five years, depending on the vigour of the plant. Lift the plant in late spring or early summer. There will be a fleshy thick main crown with smaller fleshy rhizomes coming off it. Remove the smaller rhizomes using a sharp clean knife. Pot up the rhizomes into a loamy soil (pre-made mixes are sold at aquatic centres) and firm well. Insert the new offshoot vertically into containers just under the soil surface with the fibrous root spread out below. Cover the soil with a layer of washed pea shingle.
Sarah Durrant