What to do in your garden in August

Achillea 'Summer Pastels' from Suttons

Here’s a list of quick and easy jobs to keep your garden looking its best through August, the hottest month of the year. Many gardens reach their peak this month, and it’s a great time to take a moment to enjoy their colour, structure and scent. However, there are still plenty of flower seeds to sow in August, and if you like to grow your own healthy, fresh produce, check out our range of quick-growing vegetable seeds to sow in August too.

Flowering plants in August

  • Sow hardy annual seeds like calendula, eschscholzia (Californian poppy) and myosotis (forget-me-not) directly in their flowering positions for early blooms next year.
  • Direct sow perennial plants like cheiranthus (siberian wallflower), Cyclamen hederifolium and potentilla.
  • Sow urban cactus, cineraria, cyclamen, coleus and schizanthus this month for bright indoor container displays next year.
  • Wild flowers are great for attracting wildlife into the garden. Sow cowslips and primrose seeds in trays, and place in a cold frame before planting out.
  • Direct sow feverfew and field cornflower.
  • Cut back plants like achillea and grasses to use in dried flower arrangements. Hang the cut flowers upside down in an airy, warm place so that they can dry naturally.
  • Stake tall perennials and lilies with bamboo canes to prevent wind damage.
  • Deadhead roses regularly, trimming the flower stem back to just above the first leaf. Take stem cuttings for propagating this month.
  • Watch out for evidence of downy mildew on impatiens (busy Lizzies). If infected, remove the whole plant and burn. Remember not to compost the infected plant to avoid spreading the fungal disease. Try New Guinea impatiens ‘Divine’ for 100% downy mildew resistance.
  • Prune established wisteria now. Cut whippy fresh growth back to 30cm to encourage flower bud creation over the winter.
  • Start planning your spring flowering bulb displays for planting over the autumn.
  • Take cuttings of fuchsia plants and tender perennial plants in August; they’ll quickly root at this time of year. The resulting young plants will be sturdy and over-winter successfully on a windowsill.

Vegetables in August

  • Sow late season potatoes for crops until Christmas.
  • Enjoy peas and beans as they come to fruition this month. Replace any spent plants at the end of August with autumn onions and shallots for cropping in summer next year.
  • Sow the Japanese onion ‘Senshyu Semi-Globe Yellow’ outdoors from mid to late August for harvesting next June to July
  • Sow spring cabbage, chinese cabbage, corn salad, winter lettuce and radish seeds this month.
  • Dig up your second early potatoes this month. Maincrop potatoes can also begin to be lifted as required.
  • Watch out for the symptoms of potato blight when conditions are hot and humid. Consider planting blight resistant potatoes next year.
  • Water potato plants, especially container grown crops to keep plants healthy and yields high.
  • Pinch out the tips of climbing beans and runner beans when they reach the top of their supports. This focuses energy on producing good crops of beans.
  • Pick small, tender courgettes regularly using a sharp knife, carefully cutting them off at the base of the plant. Protect your hands from the prickly leaves and stalks by wearing gardening gloves.
  • Water everything in the garden in the mornings and evenings to avoid evaporation during the day. Any crops that are in flower or have developing fruit on them must be watered well.
  • Pinch out any side-shoots on your tomato plants regularly. Tie the leading shoots to the supports securely to avoid snapped stems. Feed your tomatoes with a high potash fertiliser and don’t let the plants go short of water.
  • Pinch out your cucumber plant side shoots just two leaves beyond any fruit that may be developing. Remove any old fruit on the plants to encourage further flowering and fruiting.

Fruit in August

  • Hoe often to keep weeds under control in the fruit patch. Water soft fruit plants regularly during dry spells.
  • Cut down canes of summer-fruiting raspberry plants that have finished cropping. Tie in new canes to plant supports and remove any old or surplus ones.
  • Root any strawberry plant runners into pots by securing them down in contact with the soil. The foliage should be removed just above the crown of each plant, clearing away any debris or dead leaves. See our strawberry growing guide for more.
  • Tie in grape vines to support any new growth and the weight of developing fruit.
  • Prune back the main shoots and side shoots of gooseberry plants to five leaves, to encourage the production of fruiting shoots for next season.

Pots, baskets, and containers in August

  • Water all your container plants thoroughly at least once a day.
  • Soak any pots that become bone dry, especially terracotta pots. Water will run off the surface of dry compost, so place dry pots, baskets and containers in a wheelbarrow of water, and leave them to soak until the compost is moist once more.
  • Deadhead spent blooms and damaged foliage to keep your container displays looking fresh.
  • Check containers for nesting ants or vine weevil if plants display a lack of vigour. In the case of ants, stand pots above the water level in large saucers of water. Treat compost with a biological pest control to remove vine weevils.

August lawn care

  • Cut the grass more than once a week to create a fine finish to your lawn. Remove weeds and, if required, fill any holes with a gritty compost followed by a small amount of repairing grass seed.
  • Set your lawn mower blades a little higher in hot dry weather to avoid browning.
  • Remove only 13mm (½”) of top growth from the lawn after long periods of not cutting. Follow this with another light cut a week or so later before cutting at the recommended height.
  • Prepare sites for new lawns. The end of August and early September are the ideal times for sowing lawn seed.
  • Remove established weeds with an effective glyphosate free weed killer or moss killer.

General August garden jobs

  • Cuttings of fuchsias and tender perennials can still be taken which will quickly root at this time of year. The resulting young plants will be sturdy and over-winter successfully on a windowsill.
  • Cuttings can be taken now of houseplants such as coleus.
  • If plants being grown in patio pots are not doing as well as expected, this could be caused by either ants nesting in them or vine weevil. Preventative action should be taken and in the case of ants the pots could be stood, above the water level in large saucers of water, and in the case of vine weevil treat the compost with a biological pest control.
  • Going away on holiday and there’s no one to water your plants in the greenhouse or conservatory, then it may be worth considering one of the many watering devices available while away such as Watering Mats, Micro-drip Watering System & Timer Set, Watering Spike, Adjustable Drip Feeder.
  • In the case of containers and hanging baskets it is well worth moving them to a situation where they are shaded and out of full sunshine.
  • To prevent plants that are in a greenhouse becoming scorched, which can occur if the leaves are wet, on hot days either place netting or use a shade paint on the outside of the glass. In this instance, please remember to water plants carefully, it is always advisable on hot days to damp down the floor of the greenhouse as this will increase humidity.
  • This is an ideal time to clean out any empty water-butts so that any dirt that may be trapped at the bottom is removed.
  • Use a net to remove any dead flowers or leaves.
  • Overgrown pond plants can be thinned, and it may prove useful to take note of any waterlilies which will require dividing next spring.
  • Feed fish regularly, taking care not to over-feed, with a varied diet to build them up. Any food remaining in the pond after ten minutes should be removed.
  • To help aerate the water and keep fish healthy top up water levels.
  • Oxygen can be increased by letting water gently fall into the pond from a hose at a height approximately 1m (3′).
  • It may prove necessary to increase the amount of oxygen to fish and plants during thundery weather in which case leaving the fountain running overnight will prove helpful.
  • If you haven’t a water fountain then a gentle spray using a hose over the surface from time to time will prove beneficial.

August pond care

  • Thin overgrown pond plants and take note of any water lilies flowering. Divide these plants next spring.
  • Feed fish regularly with a varied diet to build them up. Remove any food remaining in the pond after ten minutes.
  • Top up water levels to aerate the water and keep fish healthy. Increase oxygen levels by letting water gently fall into the pond from a hose at a height approximately 1m (3′).
  • It may prove necessary to increase the amount of oxygen in your pond for fish and plants during periods of low pressure. Leave the fountain running overnight or use a gentle spray setting on your hosepipe.
Lead image: Achillea ‘Summer Pastels’ from Suttons
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