This month in your Garden - May

A venerable west-country gardener once explained that gardens are at their most beautiful on the 17th May, afterwards descending into over-maturity and vulgarity. Whilst I hate to argue with experience, I don't quite agree: surely it's both the lush freshness of May and the promise of more to come that makes this month so special.

Plant dahlias, cannas and other summer-flowering bulbs and tubers. Dahlias in particular have made a real comeback in recent years and are very satisfying to grow, rewarding every bit of the extra care with a brilliant display of flowers in late summer and autumn.

• For the most reliable results start tubers into growth in pots or trays as soon as possible.
• When the tubers have produced sturdy shoots, plant them in a sheltered position in full sun. Prepare the planting holes carefully, adding as much compost or well-rotted manure as you can spare.
• Tall varieties will need support. A single stake is usually enough, which it’s worth inserting when planting to avoid damaging the tuber later.
• Provide protection from slugs and snails, which unfortunately find all parts of the plant delicious.
• Water during dry spells, applying a liquid fertilizer at least once a month.
• Deadhead regularly, but take care not to remove unopened buds: spent flowers are usually pointed, unopened buds are round.
• Flowering continues until the top growth is killed by frost. Tubers may survive outdoors in Henfield, particularly on well-drained soils, or they can be lifted and stored in a cool, frost-free place.

Plant up hanging baskets, window boxes and other containers with bedding plants, but be prepared to protect them in the (unlikely) event of a late frost.

Prune spring flowering shrubs like forsythia and flowering currant as soon as the flowers have faded.

Watch out for lily beetle damage on lilies and fritillarias. The beetles will drop to the ground as soon as they are disturbed, so cup your hand underneath to catch them as they fall. Sprays containing the systemic insecticides imidacloprid or thiacloprid are also effective.

Keep on weeding!

Most tender crops can be sown this month, including runner beans, french beans, sweet corn and courgettes. Other seeds to sow include cauliflowers, leeks and sprouting broccoli.

Salad crops develop quickly but do not last long once mature. To ensure a good succession, sow a short row of seed every week or two.

Earth up potatoes by using a hoe or rake to pile loose soil around the base of the plants. This is not absolutely necessary, but done regularly will increase yield, control weeds and help develop an open soil texture for the crops that follow.

Glasshouse

Harden off plants raised indoors, planting them in their final positions outside towards the end of the month. Acclimatise them gradually by moving them into a cold frame for a couple of weeks, opening the lid each morning and closing again at night. If you don’t have a cold frame, put your plants in a sheltered spot outdoors and cover with fleece at night.

Ensure your greenhouse is adequately ventilated, as temperatures can quickly soar to damaging levels on sunny days. Blinds (ideally positioned on the outside of the glass) or shade paint will help control temperatures, but consider what you intend to grow before applying the paint: cucumbers and melons appreciate the diffuse light, but tomatoes and chillies may suffer.

Keep an eagle eye on watering, as small containers dry out very quickly in warm weather. Standing plants in large trays lined with soaked capillary matting, available from any garden centre, makes this job much simpler.

Lawns

Mow and edge regularly. Little and often is best: at least once a week for high quality turf, or every 10-14 days for general purpose lawns.

Water newly laid turf or freshly germinated grass seed during dry spells. It’s not too late to establish a new lawn, but watering will become increasingly important (and laborious) as summer advances.

Remove occasional weeds by hand – an old knife is ideal for the job – or by using a spot-treatment lawn weed killer.