As world news get grimmer by the day, the promise of a bountiful food garden is a solace indeed. If you can find the space this year, why not also plant flowers for cheerful bouquets, from sweet peas with their wonderful scent, to cosmos, daisies and many others. Some, such as calendula and coreopsis are particularly good for feeding pollinators and other beneficial insects. Start annuals from seed indoors right now and plant dahlias and gladiolus any time (they are now coming into local garden centres). Cosmos and calendula, in particular, can be interplanted with the larger vegetables, such as broccoli and cabbage.
Despite the occasional warm sunny day, the soil is still too cold and wet to plant. When to plant depends on how warm the soil is—and so far, with nights close to freezing, the soil is really cold. While you can set out hardy perennials this month, such as strawberries, other berries and fruit trees, the soil is too cold for vegetable seeds to germinate or for seedlings to grow.
By all means, start seeds of tomatoes, peppers, various flowers indoor or in a greenhouse this month. If you haven’t done so already, it is not too late to start seeds of peas, cabbage, lettuce, leeks and onions indoors. Meanwhile, rake the mulch from beds you want to plant first to let the soil warm up and dry out. It is a good idea to sprinkle a little iron phosphate slug bait on these beds to control slugs before you put out seeds or seedlings. Laying clear plastic down on the soil also helps to warm up and dry out the soil if you are in a hurry to plant. For gardeners that currently have overwintered crops (kale, chard, spinach, lettuce, radicchio, carrots, beets, cabbage, leeks, Brussels sprouts, cauliflower, broccoli, etc.), there is no need to rush to plant more. A few thing you might be in a hurry to plant, however, are peas and potatoes. Start pea seeds (and sweet peas) indoors in trays of vermiculite or perlite and grow them to several inches in height. By that time the soil should be warm enough to put them out and there will be fewer cutworms around to cut down your seedlings. Set some seed potatoes for an early planting indoors on a windowsill for a few weeks to develop strong dark green sprouts before planting.
If you have a really warm garden bed (e.g., up against a building foundation) or you have a coldframe or greenhouse, the most reliable early crops to sow are annuals: lettuce, spinach, Chinese cabbage and other annuals in the cabbage/mustard family. Planting hardy biennial vegetables (chard, kale, onions, leeks, cabbage) too early often results in a crop failure later because these plants may bolt (send up premature flower stalks) in mid-summer if they experience a week or two of chilly weather later this spring. This isn’t a risk when you sow these biennial crops outdoors in May because it doesn’t get cold enough at that time of year to stimulate this response.
Mulch overwintered root crops: Right now we don’t want carrots, beets and other roots in the garden to get the idea that spring is here or they will start growing. Fluffing up the mulch and adding more over these beds helps to keep them cool. By the end of March, however, it is hard to convince them spring hasn’t arrived so about then I harvest the remaining roots and store them in the refrigerator. Roots left in the ground continue to be edible, but they lose their sweetness as they sprout lots of little roots and develop a spring flower stalk.
Grow your own onion sets: When planning your garden this year, consider growing your own onion sets (those small onions you see in the garden centres in the spring). This makes sure you don’t import the dreaded white rot disease into your garden on field grown sets. It takes very little space because you sow them close together so the bulbs stay tiny. Choose good storage varieties for this purpose. I plant about a square foot of garden bed in mid-May with seeds of my favorite yellow onion [‘Sturon’, an open pollinated variety from William Dam Seeds]. Sow densely, about 3 seeds per square inch, in average garden soil that has not had compost or fertilizers added this year. The dense planting and late start keeps bulbs small: dime size sets are ideal. When the leaves wither and fall over in late summer, harvest and cure the sets the same as for crop onions. Next spring, plant the smallest of the sets for the crop and keep the larger sets for growing as scallions over the summer. Because the larger the bulb, the more likely it is to send up a flower stalk in the summer, I keep these aside and plant a dozen or so at a time every couple of weeks over the summer. They grow into lovely scallions for summer salads. I even held some until this winter and planted them in my greenhouse and now have early scallions ready to harvest.
A note on these emails: I don’t repeat everything that might be relevant for a particular month every year. To see other information that might be useful you can always check my archive of past messages: In particular, for my notes on why “average frost free dates” are not a useful concept for coastal gardeners, see my March 22, 2019 message.