With April here and a really warm day or two this week, spring is unfolding rapidly and some gardening milestones are coming up soon:

Seed starting: If you are growing your own seedlings, the first week of April is a good time to start seeds of squash, cucumbers, melons, sweet basil indoors for plants destined for the outdoor garden. You might have already started these plants if they are destined to be planted in a greenhouse for the summer.

Many gardeners have set out first plantings of peas, lettuce, spinach, potatoes, but if you haven’t, not to worry—there is plenty of time to get these going. The warmer the soil is when you plant, the faster plants grow anyway. Looking ahead, I usually plant onion sets and leek and onion seedlings in my garden the second week of April. For good sized onions, you need to plant in time to allow them to grow a good root system before the really long days of June cause them to focus on making bulbs. The later onions are planted in the spring, the smaller the bulbs tend to be; onions planted after late May, might not even ‘bulb up’ at all.

Depending on the weather, I plan to set out my early cabbage, cauliflower and broccoli plants next week. I will be watching the night time temperature in case they need to be protected under cloches or floating row cover some nights (any forecast of 3oC/37oF or lower would get me out to the garden with covers as that could result in ground frost in low spots at my elevation). To prepare the seedlings, I have been setting them outdoors in the sun for a couple of hours on the warmest days to get the leaf cells used to full sun. Gradual exposure to sunshine stimulates the leave to develop sunscreen chemicals in the cells (just as getting a tan does for us) so seedlings are less likely to be injured by sunburn when they are planted outdoors. This is what sunburn looks like on squash leaves.

There are a couple of pest management milestones coming up:

Tent caterpillars: By about mid-April the caterpillars start hatching from egg masses on tree branches. The clusters of tiny black caterpillars that emerge are easy to see on the small pads of webbing they spin at this stage. If you can reach them, just pull them off and drop them in soapy water (wear gloves as the caterpillars are covered with irritating hairs). If you can’t reach them, use a pole pruner to snip out the branch with the nest.

Imported Currantworm/AKA Gooseberry Sawfly: If leaves of your gooseberry or currant bushes were chewed up last summer, it is likely the caterpillar-like larvae of this insect. The adults will start laying eggs soon and this is the best time to nip this problem in the bud, so to speak. From mid-April, continuing for the next 3-4 weeks, I look for eggs laid on the leaves and destroy them before they hatch. This is what to look for.

Currant sawfly eggs on leaf veins

You may need a magnifying glass or use the zoom function on a phone camera to magnify the leaves enough to see the eggs (or at least put on your reading glasses...). The eggs are quite distinctive, looking like tiny stitches of dental floss along the leaf veins on the underside of small, new leaves in the lower part of the bush. From above, the leaf veins look a bit burned so that’s another clue for which leaves to turn over and search for eggs. Each sawfly female lays a lot of eggs, but concentrated on just a few leaves, therefore once you pull off and destroy those leaves, that’s the end of it. If you do a really thorough job of intercepting the eggs this spring, not only will your plants not suffer damage this season, but you may not have sawflies overwintering to lay eggs next year. If you miss some of the eggs and the larvae chew on leaves, they are very hard to see, being exactly the same green as the leaves they are eating. Though they do look like caterpillars, trying to use the bacterial spray (BTK) for caterpillars has no effect on them.

Greenhouses: A spring heat shock is a great way to clear out some difficult pests that might be overwintering in the greenhouses structure (such as spider mites) or in upper layers of soil or other damp crevices (e.g., pillbugs). If all plants in your greenhouse are in pots, it is easy to move them out, close up the doors and vents and let the greenhouse heat up inside for a couple of sunny days. Temperatures easily reach 45oC [113oF] inside! Make very sure any plants you put back in the greenhouse after the heat shock are clear of pests. For greenhouses like mine, with plants growing in a soil bed, heating will need to be longer (4-7 days) to dry out the surface layer of soil. I plan my heat treatment for the changeover period from winter to summer plantings, which usually works out to be about April 15 in my greenhouse. I do a final big harvest of chard, lettuce and other salad greens still in the greenhouse (most have bolted by then) and then clear the bed, removing all vegetation and surface mulch. Until the heat treatment is over I keep the tomatoes, peppers, basil (my usual summer greenhouse crops) in pots on a sunny windowsill or put them outdoors during the day and bring them indoors at night. After the heat shock, I amend the soil with compost and then plant up the summer crops.