April 2023
April 21, 2023 Onions, Carrots, Spring Pests
Like the last two springs, this year is also off to a late, cold start. With the Pacific circulation projected to change over from the La Nina pattern to an El Nino pattern over the summer, we can expect a shift to the warmer, drier weather typical of El Nino, but whether it will be a rapid shift in June or a slow transition over the season isn’t yet known. In any case, it is still too cold to plant much, but after the weekend the weather looks much more promising to sow or transplant the hardier vegetables: lettuce, spinach, radishes, mustards, kale and other salad-y plants, peas, Chinese cabbage, potatoes. Although hardy, Swiss chard is readily vernalized by cool weather (see below for more of an explanation) so I always wait until the first week of May to sow the new crop to avoid the risk of plants bolting to seed this summer.
It is getting to past time to plant onions (both sets and seedlings). Onion varieties grown at our northern latitude form bulbs in response to the long days/short nights in the weeks around June 21. To grow good-sized bulbs, onions need to be planted as early as possible so they develop a good root system before they initiate bulbing. Onions planted too late (after mid-May) often won’t make proper bulbs at all, but they can be used up as scallions. The tricky part is that, like chard, onions are biennial plants so can respond to a period of cold spring weather by going to seed in the summer instead of making bulbs (for more on this, see my message about vernalization Feb. 20, 2022: http://www.lindagilkeson.ca/gardening_tips.html ). Premature bolting can occur when large onion sets (nickel-sized or larger) or large onion seedlings (the size of a pencil) are planted while the weather is still too cold. When smaller onion sets and seedlings experience cold weather, they are too small to change their developmental pathway so they don’t go to seed after a cold spell, but if planted too early they might not survive at all. With the warmer week coming, plan to plant all onion family sets and seedlings, including leeks, if you haven’t put them in already.
Grow your own onion sets: These miniature onions are grown from seed sown directly in the garden one year, then cured and stored like crop onions for planting out the following year. By growing your own sets you can have exactly the varieties you want, it saves time and space in the garden because they mature a month earlier than crop onions grown from seed, and, most importantly, it avoids the risk of importing root diseases to your garden on field-grown sets from elsewhere. To keep these little onions as small as possible, sow them late to keep them small, but not so late that they won’t make bulbs. I sow them the first week of May as I find that seeds sown after mid-May usually don’t make bulbs. Choose a storage variety, sow very densely, 3-5 seeds per square inch, in good garden soil, but don’t fertilize or amend the soil with compost before sowing. You can grow a lot of onion sets in a 1-foot square patch! Harvest and cure the tiny bulbs at the same time as crop onions and store them in a dry, cool place until planting next year. There are always a few sets that grow too big (as described above), but I set those aside and plant a dozen or so of those now and them throughout the year to use as scallions (this even works in a winter greenhouse).\
The carrot conundrum: Carrots are tricky because it can be hard to get a good stand of seedlings started; after that they are fairly easy to grow. Carrots can be sown from now until the first week of July. Because carrot seeds are slow to germinate (10-14 days in the spring), providing good conditions for the entire germination period requires care. The soil must be evenly moist during the entire germination period and not allowed to get too hot as carrot seeds won’t germinate if soil is too warm. While warm soil is usually a concern for later plantings, we have had heat waves occur as early as the first week of May that wiped out germinating carrots. To maintain cool, moist soil, be ready to cover seedbeds with burlap, white plastic (such as cut open compost bags), or other shading material should there be high temperatures during the germination period.
Once germinated, tiny carrot seedlings and others, such as lettuce and beets, may be scoffed up by slugs, cutworms, or pillbugs. To avoid cutworms, sow after the first of May as cutworms have developed to the pupal stage by then and have stopped feeding. To deal with slugs, I step up slug patrols before carrots and other seeds are planted. Immediately after sowing carrots, I also sprinkle iron/ferric phosphate slug bait granules over the seedbed to control slugs during the period before carrots emerge. There isn’t an easy solution for pillbugs, but if cutworms and slugs have been ruled out and you are still losing tiny seedlings, go out after dark with a flashlight to see if what’s eating them. If there are a lot of pillbugs, you may have to resort to starting carrots in seed trays and transplanting them, at least for the early crop. Later on in the summer, with faster germination and warmer and drier conditions, pillbugs are much less of a problem. They can only chew tiny seedlings so the quicker seedlings grow, the sooner they outgrow the risk of harm. It is a myth that spreading cornmeal on the soil kills pillbugs, but they are attracted to fermenting starch so it might deflect them from eating seedlings–on the other hand, it is just as likely to attract even more pillbugs to eat seedlings. Rotting wood is a haven for pillbugs (they feed on fungi, on decaying, as well as living, plant material). To reduce their numbers, remove all rotting wood in or around the garden and replace decaying wood on raised beds with non-wooden materials (or don’t use sides on the raised beds at all). Diatomaceous earth (silicon dioxide) is a dust that works on pillbugs because it causes them to dry up, but I never use it outdoors because it also kills insects, including the many beneficial species, that might walk across it. If you do use this pesticide for pillbugs, limit it to just the immediate row or patch of soil where carrot seeds have been sown. Another pesticide option if you are a US gardener is iron phosphate slug bait that has Spinosad included for pillbug control (not available in Canada).
Prevent root fly attack: Cabbage root maggot and carrot rust fly are two common spring pests to watch out for. Carrot rust fly attacks roots of carrots, parsnips, parsley, celery, dill and related plants. Cabbage root maggots attacks roots of mustard/cabbage family, including radishes and turnips (for photos, see: http://www.lindagilkeson.ca/book_photos.html#root_feeders ). The adult root flies come out at dusk to lay eggs at the soil line around the stems of their host plants. From there, the maggots burrow into the roots; damage ranges from slight stunting to complete loss of plants. There are 2 or 3 generations a year, with the late summer/fall generation being the largest and most damaging. There is a lot of detail in my “Spring Pest Edition” message, April 25, 2021 on how to use insect netting and stem barriers to prevent damage from these pests. I won’t repeat it all here, but I have been asked whether seedlings are at risk of being attacked before they are set out in the garden. Bearing in mind that insect netting has to be in place before the flies lay eggs, the question is whether seedlings need to be kept under netting. While seedlings are indoors they are obviously safe, but what about when they are moved outdoors to harden off or when they are grown in cold frames or greenhouses that are open during the day? This early in the spring, overwintering flies are not about, but they are likely to be emerging in the next week of warm weather. The flies don’t come out to lay eggs until dusk, however, so seedlings set outdoors in the sun during the day, but brought indoors or put into a closed greenhouse by late afternoon would be safe from attack. The same goes for seedlings in cold frames or greenhouses that are closed up at night. Seedlings left outdoors on a warm evening should be covered with insect netting or floating row cover to prevent eggs from being laid at the base of the stems—but if evenings are that warm, it would be much better to plant them and put the barrier in place at transplanting time. Seeds sown directly in the garden should be covered with insect netting or floating row covers before the first shoots appear because the adult root flies can detect tiny plants.
Tent caterpillars: In some areas, such as Salt Spring, tent caterpillars are having a high population year again this year. The eggs are starting to hatch now and the first clumps of tiny fuzzy black caterpillars are beginning to feed on leaf buds. The webs are small, but not hard to see on bare branches. Keep inspecting apples and other fruit trees for nests so you can remove them as early as possible. If you can reach them, pull the small nests off the branches (use gloves) and drop the caterpillars in soapy water; if you can’t reach them by hand, prune them out. Lots more details on tent caterpillars are in my May 24, 2021 message.
Plan for summer: We can expect some heat waves this summer, so now is a good time to plan how you are going to protect vegetables from the heat this year. Lace curtains or tablecloths work fine, but it may take some time to scour thrift shops for such fabrics. If buying horticultural shade cloth, look for material that provides 30% to 50% shade. Shade fabrics range from 30-80% shading so be sure to get material that provides 50% or less shade (the higher shade factor fabrics are for delicate ornamental, ferns, orchids, etc., not vegetables). Knitted monofilament fabrics are light weight, tough and durable for many years; they can be laid directly on top of larger plants or supported on stakes or hoops over seedlings. I don’t recommend woven polypropylene materials: when cut, the edges unravels bits of plastic all over the garden and I found that if laid on top of plants they heat up enough to burn leaves where the fabric touches. Oh, and no, don’t plan to use floating row cover to shade things—it is designed to hold in heat.
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