The normal vegetative methods of increasing aquatic plants (by division or from cuttings and eyes) are all quite easily executed, even if your facilities are quite basic. For the most part, a good light window ledge is all that is necessary to raise good-quality plants.
Almost all aquatic and bog garden plants can be increased by division in the spring. This is simply the process by which the crown of the plant is divided into two or more pieces, which are potted or planted individually. With aquatic plants such as reedmaces and rushes, which have creeping root systems, this involves removing a length of rootstock with a terminal shoot attached and planting it separately. Plants like iris, water plantain and marsh marigold, which grow in clumps, can simply be separated by hand or with a trowel, rather like herbaceous plants.
This applies to most of the bog garden plants, too, established clumps being prised apart during the dormant season and the outer, more vigorous, young pieces being replanted.
A number of bog garden plants can be readily increased by taking root cuttings. This can be done in addition to division or, in some cases, as a substitute if a plant has not developed to the stage where it requires dividing. Of all the bog garden plants, it is the drumstick and candelabra primulas that benefit most from being increased by root cuttings. However, many vigorous perennials with fleshy, thong-like roots may also respond to this propagation method.
Root cuttings should be removed during the dormant season, the parent plant being lifted and suitable pieces of root removed. Then the adult plant is returned to the garden. The best roots to use are those that are no thicker than a pencil, but not so thin that they are likely to dry out before sprouting. Place pieces of root, about 2.5cm (1in) long, horizontally in trays of good seed compost, cover lightly with more compost, water, then place them in a cold frame. Within a few weeks, the root cuttings will start to sprout. At this stage, they can be lifted carefully and potted individually in small pots for growing on, ready to be planted out in the following autumn or spring.
A number of aquatic plants produce turions or winter storage buds. In some cases, such as with the arrowhead or flowering rush, these are primarily food storage organs. However, they are produced freely and can be separated and allowed to develop as new plants, rather than remain in clumps. With some floating plants, and several submerged aquatics, turions are a means of dispersing and redistributing the plants around the pond, a natural means of propagation with which the water gardener need not interfere.
While most marginal and bog garden plants are readily divisible, a number are much better propagated from stem cuttings. Indeed, some perennial plants, like water mint and brooklime, which can be divided successfully, make better plants if propagated each spring from short stem cuttings.
Such cuttings should be of non-flowering shoots, about 5cm (2in) long, which should be removed from the parent plant in late spring when actively growing. If inserted into a tray or pot of sandy loam, or indeed good, friable, stone-free muddy soil, and partially or completely submerged in water, rooting will take place within 10-14 days. The young plants can then be lifted, potted and grown on individually.
Submerged aquatic plants are mostly increased by taking stem cuttings during the growing season. These should be gathered into bunches and fastened together with a thin strip of lead. This is allowed to remain around the bunch of cuttings, which should be pushed into their permanent position in the compost.
All hardy waterlilies, except Nymphaea ‘Pygmaea Alba’, which must be reproduced from seed or occasionally by division, are best propagated from eyes. These are tiny growing points that occur with varying frequency along or around the rootstocks of mature hardy waterlilies. In most cases, they are rather like smaller versions of the main growing point, often with their own complement of juvenile foliage, although with Nymphaea tuberosa and its cultivars, they take the form of readily detachable, brittle rounded nodules.
Adult hardy waterlilies should be lifted during the spring or early summer, and the required number of eyes removed with a sharp knife. The wounds of both the rootstock and the eye should be dusted with powdered charcoal to reduce the risk of fungal infection. The eyes may be potted into small pots or modular trays, using a soil-based compost, and stood in a shallow container. This should be filled with water until it covers the rims of the pots. If the eyes are tiny, they will benefit from the protection of a cold frame or greenhouse during their early life. As they start to root and grow, they should be moved into progressively bigger pots and deeper water until large enough for planting in the pool.
Some of the tropical waterlilies are increased from seed, but by and large, the named cultivars are best propagated by separating young plants in the spring. The tubers should he potted and placed in a temperature of around 21°C (70°F) in a sunny spot. Within a couple of weeks, the first true floating leaves will have appeared. With finger and thumb, locate the stem-like growth connecting the young plant to the tuber. Pinch it off next to the tuber, removing the young plant with the roots intact, but leaving the tuber in its pot. The young waterlily plant should be potted up and the tuber allowed to regrow. This can he done two or three times with a tropical waterlily tuber, before a single final growth is retained for the coming season.
A number of tropical waterlilies are also viviparous, producing young planners on their leaves. These can be regularly removed and potted up as fresh plants.
1 Established plants should be carefully divided and the youngest, most vigorous portions used for propagation purposes. Old material should be discarded, even though it may be more substantial.
2 Trim the foliage of the plant back hard – this will in all probability die anyway. Cut back the roots prior to planting and remove any suspect decaying rootstock.
3 Replant the prepared division in good clean aquatic planting compost in an appropriate aquatic planting basket. Water well, driving all the air out of the compost before placing in the water.
1 Remove good healthy stems of non-flowering shoots from actively growing plants. This is best done during spring and summer when the plants are growing vigorously.
2 Clean up the foliage and gather together in small bunches up to 5cm (2in) long. Fasten neatly around the base of the stems with a thin lead strip to hold them together.
3 Plant the bunches of cuttings in aquatic planting baskets filled with compost. Bury the lead weight beneath the compost or else it will rot through the stems and the tops will float away.
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