What to do
As always at this time of the year, aphids are building up in astonishing numbers. Flea beetle is flourishing, too. Sowings of rocket can quickly be peppered with holes. Watch for blackfly on beans, thrips on peas, root fly on cabbages, Brussels sprouts and cauliflowers, and slugs and snails on everything.
Mildew may also be a problem. It has already broken out on the bits of acanthus springing up in the border where I thought I had dug it out. Roses and other herbaceous plants may also be affected. Unfortunately, fungicides work better as preventatives than cures.
There is still time to fill gaps in borders with fast-growing annuals such as clarkia and cornflower. If you have had no luck in the past with sowing direct in the ground, try scattering the seed thinly over compost in a seed tray, and waiting for the seedlings to grow in that. Then transplant them in little clumps to where you want them to grow.
Biennials such as double daisies, forget-me-nots, wallflowers and sweet Williams should be sown in drills outside, ready for a display in spring and summer next year. I am also sowing seed of a hollyhock Alcea rosea 'Nigra' (Thompson & Morgan £1.49) which is about 150cm (5ft) tall. The flowers are rich chocolate-maroon, as close to black as a hollyhock can get.
Take cuttings of pinks, pulling off non-flowering side shoots and pushing them round the edge of a 13cm (5in) pot of compost mixed with extra sand. Cover the pot with a polythene bag until the cuttings have rooted.
What to see
More than 120 private spaces are opening up as part of the London Parks and Gardens Trust Open Squares weekend. Visit the Zen Garden at the Hempel Hotel in Bayswater or Little Abbey, part of the historic Abbey Orchard site, in Westminster. At Sir John Cass's Primary School in Whitechapel, you can admire a new roof garden. One ticket (£9) gives access to all venues over the entire weekend. For full details of all the places you can visit, go to opensquares.org