In mild areas, the danger of frost has passed by the middle of the month and it is safe to plant out tender half-hardy annuals. In colder districts, delay until June. There is plenty to keep you busy in the garden now the warmer weather has arrived.
The early-flowering spring bulbs, including daffodils, narcissi and hyacinths, will have finished flowering. It is essential that the leaves are not cut back or damaged. To clear the beds, the bulbs should be lifted complete with their roots and the soil attached and transplanted to the nursery bed so that they can complete their growth cycle.
Any ovaries (the small swellings at the base of the dead flowers of all spring bulbous plants) should be pinched out in order to direct all of the plants’ energies into producing next year’s bulbs.
Polyanthus and primroses can be lifted, divided and transferred to a nursery bed for planting out again in the autumn or seed may be sown this month. Choose a semi-shaded site and keep watered throughout the summer (members of the primula family will die if allowed to dry out). Plant out chrysanthemums, dahlias and cannas.
Sow biennials and perennials including aubretia, alyssum, aquilegia, arabis, asters, campanulas,
delphiniums, foxglove, forget-menot, gypsophila, honesty, poppies,
primulas (all members), stocks (Brompton), wallflowers.
Before replanting the main flower beds, they can be dressed with compost or well-rotted manure if available. Once every three years should be sufficient for this treatment. Where the beds are not dressed, they should be treated with Growmore fertiliser.
Prune spring-flowering shrubs (such as forsythia, magnolia, lilac) immediately after the blooms have died.
Place straw under strawberries, which will also need protection from slug pellets. In wet weather, watch out for botrytis – remove and destroy affected berries. Unless needed for propagation, remove runners as soon as they are seen. Continue to remove the weeds between soft fruit bushes. Thin gooseberries as necessary and spray against sawfly. Spray raspberries liable to maggots.
In the greenhouse, ventilate as much as possible during the daytime but continue to close the windows at night. As growth approaches its most rapid phase, plants should be watered freely and given a weekly feed with liquid fertiliser. Gradually reduce the water to tender spring bulbs that have completed their flowering period.
Remove side-shoots from tomatoes. Pinch out the growing tips of melons as necessary and fertilise the female flowers by hand.
Lawns grow very rapidly this month and should be cut at least twice a week.
Pests and diseases
Keep a sharp lookout for garden pests. Many produce a first early brood from eggs laid by females which have overwintered. Treatment must be immediate because if the first brood is allowed to survive it will result in heavier infestations later in the year. Treat rose bushes if either insect or fungal infections are seen.
The beginning of the month is the last opportunity to replant water lilies and marginals. Bog gardens can still be planted this month.
Earth up early potatoes. Sow dwarf beans outside from the beginning of the month and runners from the middle. Make a final sowing of maincrop carrots, peas, beetroot, kohl rabi, leaf beet, lettuce, radish, turnips, swedes, salsify, spinach, sweet corn, summer cabbages, sprouting broccoli (purple and white), savoy, calabrese, Chinese cabbage.
Set out cabbages, leeks and other plants raised earlier in the seed beds. Towards the end of the month in milder districts when the danger of frost has passed, tomatoes, marrows, pumpkins, cucumbers and sweet corn can be planted outside.