Your organic garden in August

Water well in dry spells - especially beans, cucumbers, marrows, leeks and celery. But watch out for potato and tomato blight, as well as mildew, in warm, damp weather.

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 August and Vegetable Growing Cards for advice.

Soil

• A well composted soil, full of organic matter, holds water well, even in dry spells. Keep mulching - with lawn cuttings, light layer of compost or even straw and last year's leafmould - and only add mulches after watering.
• Now is the perfect time to sow green manures, especially if you have bare soil after harvesting. Plants such as vetch and clover will rapidly cover bare patches and fix nitrogen from the air onto root nodules. Be sure to dig them in after flowering and before seed sets. Phacelia can be sown now, will germinate quickly, and its beautiful lilac flowers are a magnet for bees and other useful insects. See Green manures for a full list and what each plant will offer - whether weed suppressant, soil improver or nitrogen fixer. The Organic Gardening Catalogue has a wide range of green manures.
• Keep hoeing off weeds before they flower and set seed. Add them to the compost heap. See below for composting perennial weeds, such as docks and dandelions.

Composting

• The compost heap should be a mix of brown and green material in a roughly 50:50 ratio. If your heap is dry, water it and then add grass clippings, nettles or comfrey leaves to speed up the decomposition process. If too wet, scrumpled cardboard or shredded/scrunched up paper will create air pockets and prevent lawn cuttings going slimey.
• Perennial weeds have roots full of minerals. Don't waste them. Add the foliage to the compost bin, and stuff the roots into a plastic sack. Add water or a urine/water mix (1 part urine/20 parts water) and tie the sack top. Leave for a month or two, until the weeds are sludgy. This gloop can now be added to the compost.
• For full advice on compost making, see Home Composting.

• Runner beans failing to set is due to lack of moisture at the roots. In dry weather, water well, at a rate of 5-10lt /sq m into the soil, twice a week. Contrary to popular belief, spraying flowers with water does not increase flower set. Plants grown over a winter compost trench (pictured) will be especially happy with their roots embedded in a rich and moist environment. It is normal for runner beans to produce more flowers than can possibly set as beans; expect a 50% loss.
• Tie in tomatoes, keep pinching out side shoots, and take off the top shoot to stop after the final truss. Keep feeding with liquid comfrey feed once a week.
• Earth up and stake tall winter greens.
• Cut away old leaves from squashes and pumpkins to help fruits ripen.
• Harvest garlic, shallots and onions. See Harvesting and Storage.

Pest and disease watch

• The fungal disease, potato late blight (Phytophthora infestans), can be a devastating disease on potatoes and tomatoes. Dark brown/ blackish round patches, often surrounded by a pale halo appear and quickly spread to rot the whole leaf and stems. The underside of the infected leaf develops a downy white coating of spores. Cut off the potato tops (haulms) and burn them. Don’t harvest any tubers for 3 weeks, as this allows the skin to set. See members' factsheet on Potato blight as well as the potato section of Pests and Diseases
• Tomatoes may also suffer from the same fungus-like oomycete blight. The fruits develop dark markings, with a dryish brown rot and sometimes a whitish-grey mould. The foliage shows dark brown/ blackish round patches, often surrounded by a pale yellow halo that quickly spreads to rot the whole leaf. The underside develops a downy white coating of spores. The fungus is not poisonous to humans, however the fruit are not pleasant to eat and will not ripen or store. Keep the plant leaves dry by watering the soil, not the leaves, and increase air flow between plants, particularly in greenhouse and polytunnel.
• Leaves and stems of plants affected by blight can be added to the compost heap; but do not compost blighted fruit, as the fungal spores can survive in seeds to grow and reproduce next spring, carrying blight onto your new crops. See the members' factsheet on Tomato blight.
• Blossom end rot patches are dark brown/ black and always occur at the bottom end of the fruit, away from the stem.
• Pick off any cabbage caterpillars. Make sure any netting is above the tallest plant, as butterflies will lay through a net/mesh if they can touch the leaves below.
• Pick off lower leaves infested with white fly. If infestations are bad, spray with insecticidal soap. (Washing up liquid is not soap; it is a powerful detergent, and designed to de-grease your chip pan! Plants' growth can be severely damaged if sprayed with a solution of water and washing up liquid.) See the members' factsheet on Cabbage whitefly.
• Use slug/snail controls not just around new sowings and plantings, but ideally a week or two before sowing or planting out.

• Keep soil around fruit trees and bushes in good condition, especially in hot dry spells this month. Container grown plants and those on dwarfing rootstocks are especially vulnerable in dry weather.
• Mulch well, but always onto wet soil. Leave a gap around the stem or trunk to allow air flow. Grass mowings, leafmould, rough compost and similar materials are all suitable mulches. This will help retain moisture, suppress weeds, and improve the soil.
• Prune plum and damson trees after fruiting. Cut out any material that is dead or diseased. Pruning plums now will reduce the risk of infection by the fungal disease Silver Leaf (Chondrostereum purpureum).

Pest & disease watch

• Make weekly inspections. Check all fruit trees and bushes for aphids and woolly aphids. See the members' factsheet on Woolly Aphid. Wipe off those you can reach. Prune out heavily infected stems and use a grease band to prevent ants from getting into the tree to 'farm' the aphids for their honeydew.
• Hang sticky juice in jars among the trees to trap wasps. There are no 'organic' ways to remove wasp nests. If possible, leave the nest alone and avoid the area. Nests die out completely over winter.
• Cut out apple twigs and leaves infected with powdery mildew. Put infected material straight into a bag to prevent the fungal spores from spreading as you prune.

• Cut back chives if showing signs of rust (orange patches up the stems). New, clean shoots will quickly re-grow.
• Prune out curled and folded leaves on bay trees to remove bay sucker eggs and nymphs. Rake up leaf litter around trees/shrubs to further remove affected leaves harbouring the insects.
• Remove mint plants showing signs of rust. This disease will persist over winter and re-infect plants next year. Re-plant with new stock and in a different part of the garden. If growing in containers, scrub out before re-using.
• Basil, parsley and coriander can still be sown this month.

• Continue to hoe off weeds as they sprout. Foliage, never seed heads, can be composted.
• Spring-flowering bulbs provide early season food for bees and other essential pollinators. They are in the catalogues now.
• August is the last month to prune ornamental trees (such as ornamental cherries, mountain ash) if they need it. This allows wounds to heal before winter and avoid the risk of silver leaf disease.

• Collect any rose leaves showing signs of black spot. Nip them off the bush and pick up from the ground to clear spores away.
• Leafcutter bees will remove large circular chunks of rose leaves. This will not affect the roses.
• This is powdery mildew season, when the soil is dry. Anything growing under roof eaves, or close to a fence/wall will often succumb. Keep well watered, even on rainy days
• Hollyhock rust (bright yellow/orange spots on leaves) can stunt plants and reduce their vigour. Control is not easy as spores travel long distances. Pick off and dispose of infected leaves on sight. If plants are heavily affected, grub out and start again next year with fresh stock. Cut plants hard back in the autumn. Never save seeds from rust-infected plants
• Pick off and destroy rosemary leaf beetle (green and purple stripes). They are active from now until the autumn.
• Earwigs are both 'good' and 'bad'. They damage flower petals on dahlias and petunias, but they are excellent predators of many fruit tree pests. So use the usual trap (an upside flower pot stuffed with straw), but instead of killing any earwigs found, take them to nearby fruit trees and release them to do their good work. No fruit trees? Just take them somewhere else away from the dahlias.

Greenhouse

• Avoid splashing water onto leaves when you irrigate. Moisture triggers spore germination of fungal diseases, such as mildews and grey mould (botrytis).
• Use biological controls to deal with greenhouse pests. Order the controls as soon as you notice the pests; don't wait for an infestation to build up. Use the predatory mite Phytoseiulius for red spider mite, the tiny wasp Aphidius for Aphids, the predatory mite Hypoaspis for control of sciarid fly, the parasitic wasp Encarsia for white fly and Cryptolaemus beetles for mealybugs. While you wait for them to arrive, rub off any pests you see.

Pond

• Keep your eyes peeled for water-lily aphids. Blast them off with a jet of water.

Lawns and hedges

• Grass is a drought survivor so don't bother to water your lawn in dry spells, even if it starts to turn yellow and brown. It will recover very quickly when the rain does come. See The organic lawn.
• In hot weather, raise the mower cutting height to at least 3-4cm. Cutting it shorter weakens the grass.