Advice
RHS Help & Advice
Planting water plants
Containers
In smaller ponds, aquatic plants benefit from being grown in containers as this prevents them becoming too large or invasive. Proprietary containers (aquatic baskets) usually have lattice sides to allow water and gas movement. All but those with a finer mesh need lining with hessian or polypropelene materials to prevent soil washing from the container.
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Soil
Compost suitable for planting aquatic plants should be a medium to heavy loam. Garden soil can be used if it is suitable and free from fertiliser and herbicides. Otherwise proprietary aquatic compost should be used which may also contain a slow-release fertiliser.
Feeding
Hungry plants such as waterlilies, benefit from regular dividing and re-potting in fresh soil. They may benefit from a supplementary feed in the spring of a specialist aquatic feed, when not being potted on, to encourage better flowering.
Planting
- Mid-spring is the best time to purchase new plants through
to early summer. At this time the water is warming up and
plants should start to grow.
- Choose an appropriate container for the size of the plant.
- For stability, ballast in the form of large rocks or
stones may be needed in the base of containers for taller
plants.
- Part fill the container with compost.
- Plants should be planted to the same depth as in the
original container, and rhizomes planted at the surface.
- Firm plants in well.
- Add shingle, or heavier pebbles as a finishing layer to prevent bottom feeders such as koi from dislodging the plants.
Deep water aquatics
These can be bought as container-grown or bare-rooted plants. Container-grown plants may need potting into larger containers. Bare-rooted plants should have old roots and large leaves removed before planting. Plants may need to be raised on bricks and lowered in stages as their leaves reach the surface, until the appropriate depth is reached.
Floating plants
Introduce
floating aquatics to the pool by placing gently on the waters
surface. Clumps may need separating first. One plant per square
metre of surface area should be sufficient. Avoid invasive
floating plants such as Azolla filiculoides
(fairy moss) and Lemna minor (duckweed), especially in larger
ponds.
Marginals
If
bought in plastic pots or small baskets, replant into
aquatic baskets. When planting bare-rooted plants in summer,
trim back the tops by half and trim the roots back to
within 2.5cm (1in) of the crown.
Submerged aquatics
Oxygenating
plants can be purchased as bunches which can be planted into
baskets to keep them in control. They will need anchoring
firmly in place. Approximately four to five bunches, each
containing three to four stems, per square metre of water
surface should be sufficient. Too much will have a negative
effect on oxygen levels. As these plants respire at night
large quantities can lead to a lack of oxygen at night in
the summer causing fish to die. Avoid invasive species such
as Myriophyllum aquaticum.