Your organic garden in April

See below for advice on soil, vegetables, fruit, herbs and flowers as well as the greenhouse and conservatory, lawns and ponds. Plus What to sow and plant in April and How to Grow Vegetables cards for advice.

Soil

• Good soil structure is vital to high quality plant growth, and walking on wet soil will compact and damage that structure. If possible, use planks to spread your weight, or wait until the soil has dried out before treading on it. Creating a bed system so that you can reach and cultivate all parts of the plot from narrow paths around the sides is ideal. This will keep your soil in tip top condition year-round, enabling you to space plants closer together. Research has found that in such a system yields are not reduced, despite the space taken by paths.
• If you have a worm bin, your worms will need more food, as they become active after the winter cold. Continue to protect them from night frosts. For everything you need to know about worms and compost Step by Step booklet Worm Composting is available from The Organic Gardening Catalogue or the Garden Organic Members' Factsheet Worm Composting.
• Rake out the uncomposted top layer of your compost heap and put to one side. Remove the ready compost from the bottom layers, bag it up and store somewhere dry. Return the un-composted stuff ready to activate all the micro-organisms that process the material. See Composting.

• Soil will still be cold after winter frost and rains. Delay seed-sowing out of doors until you can see weeds/grass growing strongly - a good sign that soil is starting to warm up at last.
• Keep on top of emerging weeds, hoeing regularly to keep them in check and prevent seeding. Dig up any 'volunteer' potato or tomato plants, growing from plant debris left in the soil from last year’s crops. They could be carrying the disease potato blight.
• Cover large weedy areas with black plastic or thick cardboard to smother growth until you have time to deal with it. Single plants, such as tomatoes, courgettes and runner beans, will grow perfectly well through the cover.
• When planning what to sow and where, remember plants grow best when the soil conditions are right. Root crops and legumes (peas and beans) should thrive without any additional feeding. Greedy feeders (potatoes, tomatoes, brassicas) benefit from a dressing of manure, well-rotted compost or an organic fertiliser. Recommended rate of use: garden compost = 1 wheelbarrow load per 5 sq m (2.5 gallons per square yard), manure = half that rate. See Planning Your Planting for helpful tips on crop rotation.
• If sowing under cover indoors or in the greenhouse, 'damping off' can be a problem in young seedlings sown indoors. Sow thinly and don’t over water. Overcrowding and damp conditions promote fungus growth.
• Use cloches (or frames) with netting to protect brassicas from pigeon damage, and fleece to protect from flea beetle, cabbage root fly or aphids.
• In warm areas, watch out for asparagus beetle towards the end of the month. Pick off adults and larvae on sight.
• Slug control: Use all available methods to protect your new young plants. See Slugs in Pests and Diseases.
• Where leek moth or allium leaf miner have been active, cover seedlings with fleece to protect them from egg-laying adults in April.

• Blossom in the fruit garden is one of the most beautiful sights in April. Every tree ablaze with flowers, holding the promise of the crops to come. Protect blossom when frost is forecast. Small trees or wall/trellis-trained trees can be covered overnight with fleece or other light material. Remove the cover during the day to allow pollinating insects to do their work.
• Remove blossom from newly planted fruit trees to conserve energy. In year 1 the trees need to focus on establishing a good root system. Water them, and any fruit bushes or canes in dry weather. Wall-trained trees or fruit in containers are particularly prone to drying out.
• Keep an area of at least 1m x 1m weed free around all fruit trees and bushes. Weeds and grass compete for food and water and can stunt the growth of a tree or bush. Apply straw mulches around/under established trees and fruit bushes, keeping a 15cm clear area around the tree trunk to deter mice.
• Top-dress container-growing fruit, using compost made up of equal quantities of loam, garden compost, coir and sharp grit.
• To avoid silver-leaf disease, wait until mid-May to prune cherries and plums and others in the Prunus family.
• Spring warmth will trigger a range of insect and disease problems, such as:
  • Aphids: Wipe off insects by hand (if possible) or hose off with a strong jet of water.
  • Woolly aphid: Wipe off any white fluffy clusters on apple stems and branches
  • Blackcurrant big bud: Dig up affected plants and dispose of via the green waste bin. Resistant cultivars include: 'Foxendown', 'Farleigh', or 'Ben Hope'
  • Apple powdery mildew: Pick off leaves and prune affected shoots
  • Peach leaf curl: Protect shoots from rain which splashes spores onto new growth. Cover wall-trained peach, nectarine and almond trees from before bud-burst, until the leaves have appeared. The cover should be open at the sides to allow access for pollinating insects

For more help, see Garden Organic members' factsheet Fruit Management.

• Herbs in flower make excellent bee and beneficial-insect attractants.
• Add grit to improve drainage in heavy soils. For leafy herbs (basil, parsley, chervil, coriander), feed the soil with garden compost or rotted manure. Rate: Compost – 2 standard buckets per sq m. Manure – 1 standard bucket per sq m.
• Top-dress herbs in containers with a 50/50 mixture of new potting compost and garden compost. Scrape off 3cm/2ins of the existing potting compost, and replace with the new material.
• Mint rust can continue from one year to the next. Dig out and discard any plants with yellow/orange pustules on the leaves. Buy fresh plants (or start your own from seed) and grow in a new location.

• Feed the soil, using homemade garden compost, or well-rotted manure (not both), around established plants, and in planting holes for new plants. Rate of use – Compost: 1 standard garden bucket per sq m. Manure: half that amount.
• Mulch well, once soil is warm and still moist. Depth of mulch: 6cm/3ins if possible. Ideal materials - leafmould or municipal green waste compost. This will suppress weeds and help retain moisture levels right through the summer months.
• Hoe weeds on sight. Deal with annual weeds before they can seed.
• Slugs and snails are getting active. Protect tender young delphiniums and hostas in particular. See Slugs in the Pests and Diseases page.
• Buy new peat free potting compost for any seed-sowing. Last year's material will have deteriorated over winter. Sow insect-attractant annuals to attract beneficial insects and especially bees.
• Top-dress plants in containers. Use a 50/50 mixture of new potting compost and garden compost. Scrape off 3cm/2ins of the existing growing medium, and replace with the new material.

• Aphids of all sorts will be on the increase this month. Before summer predators such as ladybirds and wasps are ready to eat them, use hand picking/squishing to control an infestation build-up, rather than resort to toxic sprays.
• Flowers in all parts of the garden will attract beneficial predators, such as hoverflies, and thus avoid the need for harmful pesticide sprays. The poached-egg flower, Limnanthes douglasii will provide an early feast. The sooner you fill your garden with the pest-eaters, the sooner you'll get the pests under control.
• Insects to encourage are ladybirds (will eat aphids), beetles (will eat slugs) and wasps - which will devour hundreds of grubs and flies in the course of a summer. A healthy garden is filled with a huge range of wildlife, ugly and beautiful, a balance that keeps the garden flourishing.
• Cut out any branches showing signs of coral spot and clear away dead plant tissue where this disease can take hold. Dieback appearing on woody plants after the cold season should also be cut out, down to healthy growth.
• Put out slug traps a week or two before making new sowings and plantings and check them regularly - especially in damp weather - to keep topped up with bait such as beer or formulated bait.

Greenhouse

• Water seedlings in pots and trays from below to avoid fungal diseases developing on wet foliage.
• Prick out once leaves are large enough to handle and plant out when well-established.
• Some biological controls can be used this month, but make sure the temperatures are warm enough. The predatory mite Phytoselius will control red spider mite; the tiny wasp Aphidius for aphids; and the predatory mite Hypoaspis for control of sciarid fly. See also the Garden Organic members' factsheets Glasshouse red spider mite, Aphids, Sciarid fly.
• Wait until May to use other biological controls, as they require slightly higher temperatures to survive and thrive.
• Aphids are active this month. Continue to wipe off and squash wherever and whenever possible.
• Check all containers for pupating vine weevils, especially where you grew fuchsias last season. They look like translucent woodlice. Turn out pots completely and sift through the soil. Squash any that you find.

Pond

• Continue to remove blanket and duck weed but watch out for frog spawn.
• Provide a ramp, in ponds with sheer sides, so frogs and other creatures can climb out easily.

Lawns and hedges

• Continue to feed your organic lawn if it grew poorly last year. Try lawn treatment from The Organic Gardening Catalogue. It has N; 9%, P; 3%, K: 3% and is an ideal organic spring feed. Alternatively, scatter sieved garden compost over the lawn, and brush or rake in.
• A patch of unmown long grass adds to the bio-diversity in your organic garden. Butterflies, for instance, like to lay eggs in flowering grasses.
• Feed any hedges with a garden compost, or well-rotted manure mulch.
• Moss in lawns is a symptom of an underlying problem, such as:
  
  • Compaction: aerate the lawn now, and again in autumn. Brush in material such as leafmould, green waste, or even old potting compost. Do this annually from now on.
  • Too-close mowing: raise the blades on the mower. Keep them to a height of about 3cm.
  • Acid conditions: test your soil. Most garden centres sell pH testing kits these days. If the soil is very acid, aerate then brush dolomite limestone into the holes.
  • Heavy shade and damp: not always easy to alter. But consider removing the grass entirely in these areas and replacing with plants that will tolerate these conditions Some grass varieties will tolerate shade.
• Leave mowings on the lawn for worms to take down into the soil - they can provide 70% of the lawn's nitrogen needs over summer.

Houseplants

• Feed houseplants from now until autumn. Large leafy plants will need a high nitrogen feed, while flowering plants need something like a tomato feed, high in potash. Comfrey tea is perfect.