How can I prevent my coriander plants from bolting?
Root disturbance is a common cause of bolting with these annual herbs, so seeds are best sown directly where you want them to grow, with repeat sowings every three weeks or so until the autumn for a constant supply. Hotweather and drought also encourage premature seed setting, so keep plants well-watered, and staked if necessary. Seed merchants offer some varieties that are slower to bolt - including Santo and Slowbolt - so look out for them.
Can you suggest a non-toxic spray for aphids?
Try combining 3/4 cup vegetable oil (such as canola) with 2 teaspoons of dishwashing detergent. Mix 1 teaspoon of this solution with 1 cup warm water in a hand-held spray bottle and apply to affected plants as needed. Aphids can also be squashed by hand (wear gloves if you are squeamish) or hosed off with a strong stream of water. Note that ladybirds, lacewings, parasitic wasps, fungal diseases and waxeyes help control aphids, but ants in the garden encourage the little pests.
