April Gardening Tasks
Spring is well and truly sprung. Throughout the woods and in the formal plantings there’s a riot of colour. The birds are nesting, taking advantage of the longer, warmer days to rear their first chicks; if you’re lucky, you’ll see wrens in the ivy round King William’s Temple and grebes performing their extraordinary mating ritual on the lake. Clouds of butterflies – tortoiseshells, commas, speckled woods and holly blues – emerge to flutter through the trees and bushes. And if you close your eyes around the great rhododendron plantations, you can smell the essence of spring long before you see the vast acreage of blooms.
Rupert Smith, A Year at Kew
As the garden warms up, any protective material remaining on tender plants can be removed. If required, they can be lifted and divided.
Once the soil has started to warm up, apply a mulch to borders to prevent weeds growing and conserve moisture. Don’t do this too quickly, however, as if the soil is still cold the mulch will stop it warming up and, as a result, inhibit plant growth. Apply the mulch after rain so that the soil is also moist.
For new borders, where the plants are small, don’t mulch during the first season, instead keep weeds under control with a hoe until the plants are fully established.
Continue taking cuttings from tubers and potting up the rooted cuttings individually as they become ready (after about 3 weeks).
Outdoors prepare dahlia beds from around the middle of the month. After adding organic matter and fertilizer, and reducing the surface to a fine tilth, mark planting positions and insert supporting stakes.
Towards the end of the month plant last year’s dormant tubers outdoors.
Once the risk of hard frosts is over, planting of later, summer-flowering bulbs such as Allium and Fritillaria may begin. Plant the bulbs in a sandy mixture if the soil is at all heavy. This will help to encourage growth of the rather delicate roots. In soil that is naturally light and sandy the bulbs need to be set quite deeply – at least two to three times the height of the bulb.
Finish pruning any shrubs that were due to be pruned in March but were not completed due to cold weather. Continue to prune early-flowering shrubs as they finish blooming.
After a hard winter there may be a number of shrubs and climbers that appear at least partly dead. It may be necessary to wait until well into this month, or even into May, for signs of new growth, so that the true extent of damage can be assessed.
Before the season gets fully underway, check climbers and wall shrubs to ensure all ties are still secure. Loosen them or re-tie, as required.
April is a good month to plant evergreens that were not planted out last September or October.
Plant evergreen and coniferous hedges and screens this month, whether the plants are bare-rooted, balled or container-grown. If the ground was not prepared last month, do this as soon as possible, following methods outlined in September and October.
The majority of half-hardy annuals should be sown now indoors. Prepare carefully before you start and make sure that trays and other tools are properly cleaned.
Hardy annuals include some of the most attractive flowers. Traditionally these have been broadcast sown where they are to grow, but a surer method is to sow them in circles or ovals. You will get a more even display and this method lends itself to quite large beds where a number of different types can be grown together. Mark out your bed roughly with a cane, tall types at the back and vice versa, and then sow in sweeping ovals which just run into each other. The other advantage of this approach is that the majority of weeds will be easy to spot.
Parsnips are one of the slowest growing vegetables and take a little time to germinate. Prepare your soil well and get them in as soon as conditions allow. An old tip is to mix parsnip and radish seed together. The radish will grow quickly, marking the rows, and be ready to harvest before the parsnips have really got going.
Brussels and summer cabbages can be sown thinly in seed trays of compost or outdoors in a firm, raked seed bed. It’s important to keep the seed bed moist. Outdoor sowings get off to a better start if protected with a cloche for the first few weeks. As the seedlings emerge, thin to prevent overcrowding. Transplant to their final growing position in a sunny sheltered spot when they are 4 – 6 inches high. Water beforehand and firm in well.
This is an ideal month to sow lettuces of the curly, crisp type. Recommended cultivars include ‘Great Lakes’, ‘Marmer’ and ‘Windermere’.
Plant onion sets early in the month. If planted too early they are more likely to produce a seedhead than a bulb. Good cultivars include ‘All-Rounder’ and ‘Sturon’.
To raise tomatoes for growing outdoors, sow the seeds in the middle of the month, using 8 cm pots or shallow trays. sow the seeds thinly, pricking them out singly into 8cm pots containing potting compost. Popular cultivars include ‘Alicante’, ‘Ronaclave’ and ‘Sweet 100’.
Sow anise outdoors, thinning to 23cm. Other outdoor sowings include good king henry, thinning to 30cm; coriander, thinning to 30cm; dill, thinning to 23cm; summer savory,thinning to 23cm; basil, thinning to 30cm. Also sow nasturtiums, placing two seeds at 30cm intervals and removing one seedling if both germinate. Now is also a good time to plant mint and comfrey.