Propagating Tubers and rhizomes

I have a garden pool which is so full of water lilies that the other plants are being swamped. Can I divide and repot them or is it necessary to start afresh?

You can remove the plants from the pond at any time between April and June. Cut the tubers into smaller pieces so that each contains a number of ‘eyes’ from which the new leaves are produced. Trim back the long, straggly roots and plant them individually in large baskets to help contain their growth.

I bought some dahlia tubers last year, and at the end of the season I lifted and stored them in a dry shed as recommended. I have been told that the best way to get more plants is to take cuttings from the old tubers. Please explain how I should do this.

Place the dahlia tubers in boxes and cover them with moist peat to just above their necks. Start them into growth in a greenhouse with a temperature of 7-10°C (45-50°F) in February. As soon as they begin to sprout, look out for good cuttings: select only strong, healthy shoots and trim them to just below a pair of leaves so that they are about 75 mm (3 in) long. Dip the bases of the cuttings in a hormone rooting powder and put them individually in small pots of sandy compost. Keep them warm and transfer them to larger pots when they are rooted. Harden them off in a cold frame or porch in May before planting them out in June.

I grew some achimenes from seed last year and have now dried off the plants for the winter. How do I start them into growth again in the spring?

Knock the dried-off plants out of their pots in spring and break up the rootballs to separate the brittle young tuberous rhizomes. Re-pot five or six of them in a 125 mm (5 in) pot in February or March. Use an ordinary potting compost and bury the rhizomes just below the surface. Place them in a temperature of 16°C (60°F) to boost them into growth, and keep them moist at all times.

I have heard that one can propagate tuberous begonias by division as well as from seed. Is that true, and, if so, how is it done?

Yes, they can be divided when they start into growth. Cut each tuber into several pieces, each with a bud, dust the cut edges with a fungicide, and leave your ‘divisions’ to dry overnight in a warm, dry room. Then plant them on the surface of some moist compost in trays. As soon as there is plenty of top-growth, transfer them individually to 125 mm (5 in) pots.

When is the best time to divide flag irises? I have a large border of them and a friend would like some.

Lift a clump of rhizomes with a fork immediately after the plants have flowered. Choose the younger parts on the outer edge of the clump (this is where most new growth is formed). Cut away the old part of the rhizomes to retain only a small portion of the current season’s growth, with some roots and a small fan of leaves attached.

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