Plant French marigolds in the greenhouse. Not only do they look pretty, but they drive away whitefly, scourge of tomato plants
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I complained recently about the difficulty that I have had in persuading amaryllis to flower in the season after the first outrageous blast of bloom. Mary Godden has written from Margate to give me the low- down. "My oldest amaryllis flowered for the 11th time this year and others are six or four years old. Not only that, my three original amaryllis have increased to seven. 'Appleblossom' has produced several bulblets which are now flowering regularly. Two or three years blind and then a flower is my experience. (I separate them.)

"I treat them all the same: a late-December start on moist compost in the airing cupboard. Move to light when shoots (sometimes a bud) are 4- 6in high. I water sparingly during this time. When a bud breaks, I water and feed with Baby Bio every week. When the flower has died I cut off the stem and continue weekly feeds until late October, early November. I then cut off the leaves one inch above the bulb and allow it to dry out in a spare bedroom. In late December I repot them and start again.

"The leaves do grow pretty long and spready. It's fortunate I have room to house them from flowering (March or April) to the end of October."

This weekend is the first of two organic gardening weekends organised by the Henry Doubleday Research Association. Scores of organic gardens will be open all over Britain including Joan Thomas's one-acre plot at March End, Doctor's Hill, Sherfield English, Romsey, Hants (01794 340255). This has vegetables, a large polytunnel and herbs. March End is open tomorrow (2-6pm), admission pounds 1. Kate and Stanley Farrow have a mixed garden of one acre which includes experimental compost heaps and a wildlife pool. Their garden at Brambles, Chipperfield Common, Kings Langley, Herts (01923 262416) is open tomorrow (2-5.30pm), admission pounds 1. Sue and Mike Stratful have a suburban garden at 44 Lois Drive, Shepperton, Middx (01932 245124) with vegetables in raised beds, fruit trees, a small pond and a solar-powered greenhouse. The garden is open tomorrow (10am-5pm), admission by donation.

New cultivars of streptocarpus and fuchsia, unusual herbaceous perennials, stunning displays of lilies, sweet peas, orchids, clematis and cacti will be shown by more than 30 top growers at the Festival of Gardening held this weekend at Hatfield House, Hatfield, Herts. Pelargoniums, euphorbias, herbs, old English roses and alpines will all compete for the honour of the Lady Salisbury Award. On both days there will be question- and-answer sessions where expert horticulturists will answer queries. The private East Garden at Hatfield is also open during the festival. It is open today (10am-6pm) and tomorrow (10am-5pm), admission pounds 4.70.