The aquatics are just the thing for lending a distinctive character to a greenhouse or a conservatory** if you build a small indoor pool.

This is easily done nowadays if you use a little artistic imagination with the help of plastics, and with care and the use of easily handled materials such as hypertufa (which has the appearance of natural-stone, but is lightweight and easily lifted).

greenhouse aquatic plant

Very natural-looking pools can be devised, complete with tinkling fountain and even fish. There are some especially delightful exotic aquatics such as tropical Nymphaea (water lilies), bur owing to the high temperatures they demand I have omitted them for practical reasons.

The following can be grown in pots stood in shallow pans or bowls kept topped up with water or where stated, grown in a pool with the pots concealed or just covered with water.

In all cases mix some crushed charcoal with the potting compost if possible.

1) Acorus Gramineus Variegatus (Sweet flag)

This is clump growing with long sword-like erect leaves, striped along the centers with creamy white. It is hardy in the unheated greenhouse and can be used in pots or to decorate the edges of ornamental pools. It is very easy to propagate by simple division of the clumps in spring.

2) Astilbe

The hybrids are beautiful decorative plants for pots, or the pool edge. In the greenhouse they produce their delightful feathery plumes in spring, outdoors in the summer.

For pot culture be sure to obtain the low growing forms. If you wish to force plants, try to get the varieties ‘Deutechland’ (white) and ‘Fanal’ (red). These can be grown in 13-cm (5-in) pots.

Pot in autumn and keep in a cold frame well watered. Take into the greenhouse at about Chrismas time and, if you wish to force, give a temperature of about 10°C (50°F) allowing this to rise a little over a few weeks if possible. Plants can be propagated by root division at repotting time.

3) Cyperus

C. altemifolius, umbrella grass, is a dainty graceful pot plant, often grown as a house plant, with long stems bearing a spread of narrow’ foliage at the top like the spines of an umbrella.

It is quite easy to raise from seed sown in spring by the usual methods It can also be propagated by root division in spring. There are variegated varieties that can only be propagated by the latter method.

In the greenhouse the plants are evergreen, but they can be used for pool edging outdoors during summer.

4) Eichhornia Speciosa

This is a weed in its native habitat and is known here as the water hyacinth, owing to the hyacinth-like spikes of lavender blue flowers. It is extremely decorative and floats on water by means of its inflated leaf bases.

The glossy heart-shaped foliage is also very attractive. Plants are often obtainable from shops specializing in tropical fish, and should be purchased from spring onwards. They can be floated on a pool or grown in water tubs or bowls. They can be put in an outdoor pool in early summer.

Overwinter the plants in bowls of wet potting compost making sure the fibrous roots are covered. The plant does best when, during summer, it is floated in shallow water so that the roots can reach down to the bottom layer of soil or compost.

In the right conditions the plants multiply themselves readily and can be divided for propagation. If the greenhouse falls below about 10 C (50CF) in winter, it is best to overwinter plants in the home.

5) Lobelia Cardinalis

It is not generally known that this attractive tall spiky scarlet flowered lobelia with reddish foliage makes a good semi-aquatic. It overwinters well in an unheated greenhouse, but can be unreliable when grown outdoors.

It is very easy to raise from seed sown in early spring, usually flowering the first year. Best flowers are usually seen on the clumpy plants that develop by the second year.

Older specimens may deteriorate. Best grown in large pots of very moist compost. Can also be planted in the moist soil around natural outdoor pools.

6) Mimulus (Musk)

The dwarf hybrids, such as ‘Royal Velvet’ are very easy to raise from seed and make wonderful, extremely exotic flowering pot plants. The flowers are freely formed very large and strikingly marked in contrasting colors.

The flowering is also fast, and fine plants will be obtained in a few weeks from seed sown in spring. To prolong the display, it is wise to stagger sowings. Grow about three seedlings to each 13-cm pot. Pots can be stood in shallow water.

7) Zantedeschia Aethiopica (Arum or Calla Lily)

This well-known florist’s flower is not a lily, although commonly thought to be by the layman. Pot the rhizomes, one to each 15cm (6-inch) pot or three to a 25cm (10-inch) pot in autumn. Just cover the rhizomes with compost and keep quite moist in the greenhouse.

Flowering time depends on overall greenhouse temperature, but is usually in spring or early summer. After flowering, put the pots outdoors and gradually reduce watering.

In autumn let the pens go quite dry and turn them out to separate the rhizomes which should have reproduced. During the growing period, the pots can be stood in a pool with the water just covering the rim if desired.