Onion thrips: These pests pierce the leaves and suck out plant juices, causing silver spots. Serious infestations result in stunted, bleached foliage that dies. Don’t plant leeks near fields of alfalfa or grain. Spray with insecticidal soap; remove weeds and debris around the garden to prevent thrips from overwintering.
Onion root maggots: Adults lay eggs at the bases of young plants. The white maggots burrow into the underground stems, causing the plants to wilt, turn yellow and possibly rot. Mulch immediately after planting to prevent the flies from laying eggs. Destroy infested plants and do a good fall cleanup.
Fungal diseases: Plant leeks in well-drained soil and always practise a four-year crop rotation (including all types of onions). Don’t water late in the day. Destroy infected plants and do a good fall cleanup.
Harvesting and storage
Growing both summer and winter varieties of leeks will extend your harvest season. Summer cultivars grow quickly, usually producing a crop in August. However, they don’t store well, won’t overwinter and need to be dug up before a heavy frost. Winter ones are larger, produce in the fall, are hardier and will survive fairly heavy frosts, and, if protected, may overwinter in parts of Canada. They also store better.
Dig up leeks with a garden fork, being careful not to damage the white shaft of the plant. When using within a week, cut off the root end and leaves, and store unwashed in a plastic bag in the refrigerator—they’ll take up less room this way. The leaves can be coarsely chopped and frozen to add to winter soup stocks.
If winter temperatures remain above –12°C, hardy varieties can be left in the garden. In colder climates, leave leeks in during the first light frosts, then dig them up before the first killing frost. Cut off the roots just below the base of the shaft and trim the leaves to eight centimetres. When stored at 0°C and 95 per cent humidity, leeks will keep for two to three months.