Gardening in July

Clematis is one of the favourite climbers of many gardeners, and if plants wilt in mid-summer it’s easy to assume they need watering. In fact, clematis wilt is a fungal disease that can quickly damage stems and even kill the entire plant. Varieties with big flowers, such as the ever-popular Clematis ‘Nelly Moser,’ are more susceptible to wilt.

With no chemicals available to control the problem, cut wilted stems back to healthy growth and bin (don’t compost) diseased prunings. Disinfect secateurs with a garden cleaner such as Jeyes Fluid after finishing the job too. It’ll help to prevent the disease from spreading around the garden.

When cordon (single-stemmed) tomato plants hit greenhouse roofs, or reach the top of canes if grown outdoors, it’s time to ‘stop’ them by nipping out the tops. Regularly pinch-out side shoots, too, as tomato plants need to put all their energy into cropping rather than producing unwanted foliage. Feed weekly with a high potash fertiliser which will encourage more flowers and fruits.

For tomatoes in greenhouses, it’s important to water daily (twice a day in hot weather). If the compost dries out or watering is erratic, swelling fruit can split or develop problems such as blossom end rot.

Butterflies going about their business in the garden are a sight to behold – apart from the cabbage white! If this butterfly is spotted on the wing above brassicas such as Brussels sprouts, cabbage and broccoli, take immediate action. Adult butterflies lay their eggs on brassica leaves (or under them) and the resulting caterpillars are highly destructive, rapidly devouring brassicas and covering plants with excrement. For maximum deterrent, net brassicas to prevent butterflies laying their eggs – but check plants thoroughly and squash any eggs already laid on leaves before pegging netting to the ground.

If iris clumps have died out in the middle, now is the perfect time to dig them up and divide, as plants should have finished flowering.

• Use a garden fork to gently ease clumps out of the ground, taking care not to damage rhizomes, then pull clumps apart. 
• Discard the oldest bits (usually in the middle) and divide young material with leaves (you’ll find the healthiest bits at the edge of clumps). 
• Cut leaves down by half, then plant a few new divisions in the gap left by the original plant. 
• Plant rhizomes horizontally with only the roots and lower half buried, as the top half of each rhizome needs to be exposed to the sun for future flowering.

Heading off on holiday this July? Simple steps can help to keep the garden alive while you’re away. Move container plants into a shady corner, stand pots in deep saucers and water well. Flowers and edibles in hot greenhouses won’t survive for more than a couple of days though, so consider installing a drip irrigation system. These clever gadgets use solar power to channel water from a nearby water butt, via pipes and ‘drippers’, into compost. Most irrigation systems allow you to set the frequency and duration of daily watering.

Strawberry plants often produce ‘runners’ – long shoots containing young plants. To bulk-up your stock of plants, fill pots with multipurpose compost and set pots into the soil close to the parent plant. Guide the runner into the pot and gently peg the young plant down with a piece of wire. Water well. Once plants have taken root and started to grow, the runner can be cut from the parent plant and discarded.

By high summer, lawns can lack vigour and lose their lush green colour, even if the grass was fed in spring. There are lots of quick-fix high nitrogen fertilisers on the market that promise rapid greening – perfect if you’re planning a barbecue or summer party. Read the instructions carefully to see if you need to leave a gap between mowing the grass and applying the fertiliser. For best results, most summer lawn feeds should be applied when the lawn is dry but rain is forecast. Don’t apply lawn fertiliser during periods of drought.

Get more expert advice on lawn care in summer >

Gluts of veg can cause a storage nightmare, so cut courgettes when they’re 10-12cm (4-5in) long. Regular picking of young courgettes extends the cropping period and avoids an autumn glut of marrows. While you’re on the veg patch, harvest radish, spring onions, runner beans, French beans and garlic. Check fruit bushes too, and pick raspberries, blackcurrants and gooseberries.

During warm, wet weather, slugs are at their most destructive and container plants can be shredded. Applying self-adhesive copper tape – a popular slug repellent – reduces the risk of slug damage for minimal effort and cost. Cut the copper tape so it’s long enough to stretch around your pot, then stick it in position – ideally just under the rim of the container. If determined snails breach the copper tape, use crushed eggshells or snail barrier granules to create a physical obstacle on the surface of compost around susceptible plants in pots.

Coleus are one of the few bedding plants that are grown for their brightly coloured foliage and not their flowers. In fact, their blue flower spikes are unattractive and insignificant. Left to bloom, coleus will run out of steam long before summer is over. So regularly pinch out flower spikes, ideally before flowers emerge, and displays will carry on until the first frosts of autumn.

However, you will definitely want to enjoy the tall, glamorous flower spikes of lupins and delphiniums. Once they’ve finished blooming, spent stems can look a mess, so cut them off promptly. You may even be rewarded with a second flush of flowers.

Agapanthus, also known as African lily, loves growing in container as well as borders, as long as they’re sitting in a sunny spot. As a general rule, evergreen agapanthus are often tender, and while plants may survive mild winters or live outdoors all-year-round in sheltered regions of the south, they are best grown in containers and overwintered in a cool greenhouse or conservatory.

Deciduous Agapanthus are widely regarded as the toughest and will grow happily in sunny borders all year round, as long as the soil is well-drained. Always check the hardiness of your chosen variety, though, to determine whether to grow it in the ground or in a plant pot.

Which variety to choose? Agapanthus ‘Fireworks’, has been bred for bigger flowers and better colour – blooming in eye-catching white and blue. A big attraction is its long flowering season, often blooming for up to three months – as late as September – long after other agapanthus have gone over. It’s tough, too, shrugging off winter lows as chilly as -10°C.

Agapanthus ‘Brilliant Blue’ is another great choice and is hardy throughout much of the UK. Semi-deciduous and compact, the variety produces an abundance of intense, deep-blue flowers. For a strikingly different agapanthus that will bring an architectural display to your borders, try ‘Black Magic’ – an evergreen that’s claimed to be one of the darkest varieties available with drooping indigo flowers, but plants may need protection from frost.

For a great display, liquid feed every two or three weeks, starting when plants come into growth in April or May and carrying on until flowers begin to colour-up. A balanced liquid fertiliser such as Miracle-Gro, Phostrogen or Flower Power will work a treat. Newly planted agapanthus will need lots of watering if it’s dry during their first year but should require less attention once established. When flowers have gone over, use secateurs to cut flowers and stalks that are spent. It’ll encourage plants to keep the show on the road for longer.

Sweet peppers are simple to grow and will fruit in glowing shades of red, yellow, green or orange. Even those who have never dabbled at grow-your-own are almost guaranteed a brilliant crop.

Sweet peppers are rich in vitamins, A, C and K. While it is possible to get a decent crop outdoors in a sunny spot, results are often superior when grown in the warmth and shelter provided by a greenhouse or conservatory. If you’ve bought young sweet pepper plants at the garden centre, simply grow them in a pot with good drainage, filled with quality multi-purpose compost.

Support plants with canes as they grow bigger, tied loosely to the main stem. When the first flowers begin to open, feed weekly with a high potash liquid fertiliser – tomato feed is ideal – and more flowers will quickly follow, leading to further crops. In hot weather, make sure that greenhouses are well ventilated, and spray water on the floor each morning because it’ll help to keep temperatures down and increase humidity.

Flowers of sweet peppers benefit from being misted with tepid tap water, which can help fruit to set in hot conditions. As for plants themselves, water regularly as needed, but don’t leave compost saturated.

It’s easy to tell when mature fruits are ripe because they’ll quickly turn from green to the colour of your chosen variety (unless it’s green, of course!). To harvest, never yank peppers from plants but use secateurs to cleanly cut the fruit’s stalk. Freshly harvested peppers are bursting with flavour, but will store for longer if kept in the kitchen or fridge – they’ll quickly deteriorate if left in the heat of a greenhouse.

The biggest threat to sweet peppers is from hungry caterpillars, which emerge in mid to late summer and ferociously attack plants. Tiny pellets of black poo on leaves are a tell-tale sign of trouble, so examine plants carefully – paying attention to the underside of leaves – and remove any offenders. Caterpillars are masters of disguise, often hiding alongside leaf stalks and stems, so take care not to miss any! In the event of a severe infestation, spray with an organic bug killer that’s approved for use on edible crops.

Whether you have a tiny terrace or traditional garden, everyone can enjoy a fruit tree/shrub in a pot – and the health benefits that this superfood brings. Now hugely popular for growing in UK gardens, sweet and juicy blueberries are rich in antioxidants, vitamins C and K, and fibre. Oh, and they’re delicious to eat fresh or cooked.

Blueberries love acidic soil, so if your soil isn’t acidic (with an ideal pH of 4-5.5) then grow in a pot, planting into a John Innes Ericaceous compost. Sit the container in a sheltered, sunny spot, water regularly (plants will thank you for rainwater rather than tap water) and come late summer to early autumn, you’ll be rewarded with a bumper crop of delicious, healthy treats.