When to cut back and when to sow: The ultimate summer garden calendar

Two gardeners with a watering can and a hand fork: Check out garden summer diary for the job you need to do (Alamy/PA)

For many summer is a time for rest and relaxation, but not if your’e a keen gardener.

As many just sit back and enjoy the garden, there are actually plenty of jobs to be done during the warmer months to keep it looking its best.

Horticulturist Nick Hamilton – son of the late legendary broadcaster and Gardeners’ World presenter Geoff Hamilton – who runs Barnsdale Gardens in Rutland, offers this gardening calendar to help you through.

From feed to cutting back, he looks at when and how you should get the tasks done.

June

Make your own liquid feed

“I use nettle feed as a growth stimulant and comfrey to encourage flower and fruit,” he says.

Hamilton uses an old onion bag (you can get them from your local market), weighed down with stones, and crams it full of the leaves before tying the handles over a bamboo cane, then laying the cane across the top of a water butt and dropping the filled bag in.

Left for two to three weeks, the resultant liquid can be drawn off at the tap of the butt and used to feed tomatoes, peppers, melons, aubergines, hanging baskets and anything else that needs more flowers.

You can also make comfrey feed just by steeping the leaves in a bucket of water.

Watch out for lily beetle

Your lilies should be growing strong by now, so be vigilant against lily beetle, which are easy to spot because they are red and can decimate the leaves of your plants. Remove and destroy any that you notice, which will hopefully keep them in check. The sooner you do it, the more control you will have. Also check leaves for any reddish-yellow larvae or eggs and remove those too.

Harvest globe artichokes

These delicious ornamental vegetables should be ripe for the picking now. Don’t leave them to become too big or they will be tough.

Continue to sow salad crops

Successional sowing will mean that you can enjoy salad throughout the summer, including radishes (which can be sown every week), lettuces (every two weeks), multi-sown beetroot and kohl rabi (every three weeks).

Look after potatoes

Earth them up, drawing soil up around them to form a ridge along the row, leaving the top 10cm of plants visible. Keep doing this regularly as they grow which will help the plant produce potatoes right up to the stems and increase your harvest.

Cut back diseased geraniums

“I find that early flowering varieties such as those of the Geranium clarkei group seem to invariably end up with their leaves absolutely covered in mildew, after flowering in May.

“The best way to counter this is not with chemicals but to give them the ‘Chelsea chop’, albeit a bit late. Cut back all the foliage as far as you can and it will regenerate very quickly with new foliage that will be completely mildew-free.”

July

Cut back herbs – but leave some for the insects

It is always a bit difficult to hit the right balance between getting what you want and providing for the wildlife in your garden, and herbs are the prime example of that, Hamilton explains.

“At this time of year some, such as oregano and mint, are beginning to become less prolific with leaf production, as they are starting to come up to flower (what the insects want).

“To keep my kitchen supply going I need to cut the plants back hard, but then that would take all the flowers away. To do my bit, where possible, I grow two clumps – one for me and one for the insects.”

Feed roses

After the first flush of flowers of repeat-flowering roses, sprinkle a handful of chicken manure pellets around the base of the plants to encourage further blooms later on in the summer.

Take semi-ripe cuttings of conifers

“As this is a time when lots of conifers are trimmed it is also an ideal time to take cuttings,” he suggests. They need to be 5-10cm (2-4 inches) long and taken with a ‘heel’, taken by holding the required shoot near the top and pulling sharply downwards, so that it is removed from the plant with part of the old stem still attached, the ‘heel’.

Trim the heel so that it is flush with the main stem of the cutting, remove a third to half the leaves, dip in organic rooting hormone and pop into a pot or seed tray containing seed and cuttings compost before watering well and putting into a cold frame.

Keep pests at bay

Pest populations can increase rapidly in summer, so keep aphids in check by either picking them off by hand (if there aren’t that many) or spray them using a proprietary natural washing up liquid diluted with water, he advises.

Water wisely

Work out which of your plants really need water during hot spells and use a watering can to water them directly at the base rather than a sprinkler, which will waste water on plants and grass which don’t need it, he suggests.

Deadhead tender perennials

To keep plants such as argyranthemum, osteospermum, cosmos and gazania flowering throughout the summer, deadhead them regularly.

Tackle cabbage white butterfly

This butterfly is now very active and can be devastating, so brassicas need protecting. If netting them is not an option, the organic answer is either a product called Dipel or nematodes, Hamilton advises.

“The nematodes work on contact and are specific to the caterpillars of the cabbage white, so it means the spray is applied to the undersides of the leaves. The Dipel, however, can be sprayed on the leaf surface as it is a bacterium that is also specific and only needs to be ingested to work,” he says.

August

Be kind to climbing roses

Hopefully they should have given you plenty of flowers, so now repay them by tying in the new shoots for flowering next year, which will protect them from wind rock. You should also continue to deadhead roses to prolong flowering.

Ventilate the greenhouse

Don’t let your prized plants succumb to fungal diseases in the greenhouse. Make sure you ventilate it well (throughout summer), opening doors and vents, to allow good air circulation.

Keep weeds under control

You may not be able to rid your beds and borders completely of pernicious weeds such as bindweed, but keep pulling them as soon as you see them so they don’t take over your garden. Hopefully, if you are vigilant, the bindweed will weaken and eventually die. Unravel it from the plants it is climbing up and pull it out at the base. Remove duck weed from ponds.

Prune early summer flowering shrubs

Shrubs including deutzia will benefit from pruning now with either shears or secateurs, to keep them neat and tidy.