Your organic garden in May

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 May and How to Grow Vegetables cards for advice.

Soil

• Keep your soil in good heart at all times and see the difference. Garden compost or well-rotted manure helps soil structure. It improves drainage in heavy clay soils, and retains moisture and nutrients in free-draining sandy or stony soils. Now is a good time to apply it. The organic material breaks down slowly over months, releasing nourishment for the plants.
• Grow fast-growing green manure plants, such as Crimson clover Trifolium incarnatum, where there are areas of bare soil - for instance where summer or autumn vegetables are yet to be planted out. If you dig it in before July, it will not only keep down weeds but also fix precious nitrogen in the soil. See Green Manures.
• Keep adding to your compost bin, making sure to mix 'greens' (lawn cuttings etc), with 'browns' (cardboard, straw and scrumpled up paper). See Home Composting.

• As the soil warms up, plant out some of the more tender crops. Some can be sown directly.
• Plant comfrey (Russian cultivar 'Bocking 14' is best). The leaves can be used as a compost activator, a mulch to feed the soil, as well as making an excellent liquid feed. See Comfrey - how to grow and use.
• Use last year’s compost to mulch on top of the soil around plants; always add mulch after rain to help keep moisture in
• .Hoe regularly to keep down weeds. Chickweed will produce 2000 seeds per plant per season if left untouched.
• Fill any empty gaps awaiting vegetables with a fast-growing cover crop of green manures. Buckwheat, mustard, phacelia or trefoil can all be sown in May if the ground is moist enough. See Green Manures.

Pest and Disease Watch

• Slug control - use all available methods to protect your new young plants. See Slugs in Pests and Diseases. It is often worth starting new plants in pots or modules, and planting out only vigorous transplants.
• Carrot fly – create a fleece barrier from sowing until mid or late June. See Carrot Fly in Pests and Diseases or the members factsheet
• Blackfly - check broad bean plants regularly and squash any blackfly seen. If the plants are flowering, pinch out the top couple of inches, blackfly and all, and bury them in the compost heap.
• Protect leek seedlings from the allium leaf miner or leek moth where either of these pests are endemic.
• When planting brassicas, use a collar on the ground to protect stems. Also erect a mesh barrier to cover plants completely to keep cabbage white butterflies from laying their eggs on leaves. Squash or pick off any you see.
• Flea beetles are also pests of brassicas (the cabbage family), and radish, rocket, mustard and other related plants. They are particularly damaging to young seedlings, especially during dry weather. See Pests and Diseases.

• Keep fleece handy to protect blossoms from late frost. Including strawberry plants. Remove during the day to let pollinating insects in.
• Keep at least 1 square metre of ground weed-free around all fruit trees and bushes - particularly young ones. This prevents grass and weeds competing for nutrients. However, established fruit trees on vigorous rootstocks will not be affected by grass growing right up to the trunk.
• Water all recently planted fruit trees - thoroughly once or twice a week rather than little and often; varieties on dwarfing rootstocks and wall-trained fruit may continue to need watering in dry weather for several years.
• Use a mulch (straw, grass cuttings etc) on moist soil round trees and soft fruit to retain moisture and deter weeds. See the members' factsheet Mulches: weed prevention and control.
• Net strawberries to deter birds, once fruits start swelling and ripening. Ensure netting is pegged down to prevent birds getting trapped or tangled up.

Pest and disease watch

• Inspect fruit bushes and plants regularly for aphids. Where possible, squish off with your fingers.
• Grow plants nearby such as Limnanthes douglasii (poached egg plant) or fennel, to attract beneficial aphid-eating insects such as ladybirds, lacewings and hoverflies.
• If you use an insecticidal soap spray, it must be sprayed directly on to the aphids to be effective.
• Put up codling moth traps in fruit trees. See members' factsheet on Codling moth.
• Pick off and destroy emerging larvae of apple and plum sawfly at petal fall. You need to catch them before they start tunnelling into fruit. Look for creamy white larvae, about 15mm long, around the fruiting spurs.
• Inspect gooseberry bushes twice-weekly for gooseberry sawfly larvae. Eggs are laid under leaves in the centre of the bush, and pinprick sized holes are the very first signs of larval damage. Pick off and destroy the tiny larvae. See members' factsheet on Gooseberry sawfly.

• Allow herbs to flower, for pollinating bees.
• Top dress herbs growing in containers. Scrape off the top 4cm/2” of compost, and replace with a 50/50 mixture of fresh potting compost (peat-free and organic) and garden compost.

• Mulch warm soil after rain to retain soil moisture and suppress weeds.
• Early May is your last chance to sow annuals as well as spring-flowering biennials (such as pansies & wallflowers).
• Hoe off any weeds before they can seed.

• Vine weevil adults will be rampant now, and laying eggs. Use nematode biological control. Use non-drying grease round the legs of greenhouse staging to prevent adult weevils crawling up.
• Use all controls at your disposal against slugs and snails, including nightly patrols. See Pests and Diseases
• Handpick Solomon's Seal sawfly off on sight. If left, they will de-foliate plants, then drop to the soil to pupate and overwinter. Break the cycle by clearing off the larvae.
• Lily beetles will make holes in leaves and damage flowering shoots. Pick off the bright red beetle adults, and wipe off their larvae, again to break the cycle. Check daily until the end of the month to be sure that all these beetles have been dealt with.
• Viburnum beetle larvae will be active now, feeding on new foliage. Pick off any larvae (creamy yellow with black markings), and trim back damaged foliage.
• Check for box blight. Symptoms include wispy grey fungus on the underside of the leaves and black streaky staining on the woody parts of the plant. (This is different to wind scorch, which just looks brown and scorched.) Affected sections should be cut out and all contaminated material disposed of.
• Hoverfly larvae can be mistaken for pests. If in doubt, leave well alone. They are voracious aphid eaters, so will be found in the middle of an aphid cluster.
• Check very carefully before either squashing or spraying. There will be beneficial creatures around, munching happily on pests on the undersides of leaves. Insecticidal soap is just as damaging to them as it is to the pests.

Greenhouse

• Remove and dispose of any dying foliage on sight. Disease prevention in a greenhouse relies on good hygiene.
• Temperatures should be high enough by now to use all types of biological controls for red spider mite, aphids and white fly.

Pond

• Tadpoles and baby newts (efts) should be maturing and leaving the pond soon. Make sure there is a sloping side so they can get out.
• Provide plenty of sheltering, moist plants around the perimeter especially if your pond is surrounded by slabs or gravel. Newly-emerged froglets will fry on sunbaked surfaces.
• Ensure that your pond has two-thirds of its surface covered by plants to keep algae at bay as light levels increase and temperatures rise. See the members' factsheet Setting up a Pond.

Lawns and hedges

• When choosing a new mower, why not go for a 'mulching' or 'recycling' mower? These machines chop up mowings very finely, then spread them evenly over the lawn. This will provide around 70% of the lawn's nitrogen needs.
• How to recycle large quantities of grass mowings:
  • Put a thin layer of mowings in your usual compost heap, but remember to add plenty of dry material too.
  • Throw the cut grass at the base of hedges where it will rot and return some goodness to the soil.
  • Use to cover thick layers of newspapers, to create a moisture-retaining mulch around trees and shrubs.
• Remember, grass is a drought survivor. Even a lawn that has turned brown, and looks wrecked, will revive once temperatures drop and rain returns in autumn.
• As birds will be nesting in hedges now, wait until later in the year before undertaking any major hedge trimming.

Houseplants

• Continue to 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.