Halton region Master Gardeners

Janet Padiak – Halton Master Gardener

April 1, 2025

April is the month to plant early vegetables that thrive in cool weather. This applies to both seed grown crops–such as peas and spinach–as well as crops started in trays such as bok choi and lettuce. These vegetables love the ample moisture of spring and are unfazed by freezing temperatures. In many cases these crops reach maturity in about 60 days and, following harvest, a summer crop can be planted in the same patch.

Cool weather vegetables are happily free of the pests that appear later in the season. Slugs and earwigs are still overwintering in the ground and are not yet chewing tender leaves. Flea beetles don’t emerge until early May and by the time that they start feeding, early-season plants are sufficiently mature to withstand the damage.

Here are some vegetables to consider planting this month:

Lettuce. Almost all lettuces thrive in cool weather and their rapid growth makes them ideal for an early crop. They come to maturity before the arrival of the long days that trigger bolting (going to seed). Lettuces can be direct seeded when the soil temperature is 10-15^o. They can also be started indoors and transplanted at the 4-leaf stage anytime in April. 

Peas. Peas are almost always direct seeded, and this can be done when the soil temperature reaches around 10^o, usually mid- to late-April. If your soil is sandy and warms quickly, you can seed earlier, but if it is heavy and clayey, then later in April is better. Plant peas closely, about 5 cm apart. Most peas like something to climb on, so insert sticks or a trellis at time of seeding. 

Spinach. Spinach loves cool weather and can germinate in soils as low as 5^o. It is the simplest plant to grow in cool weather, but as soon as the days lengthen and the soil warms, spinach stops producing leaves and sends up a flower stalk, indicating it is past its prime. Dig these up for the kitchen and plant a summer crop in the space.

Arugula. There are two genera of arugula available: the annual Eruca sativa and the perennial wild type Diplotaxis tenuifolia. Both types can be put in the ground as soon as the snow is gone and, like spinach, will germinate in soils as low as 5^o. These can be harvested at any stage from baby leaf onwards. The annual arugula, if left to go to seed, will complete its life cycle in one year, but the perennial type will remain in place all year and emerge again next year in the early spring. Both are equally tasty, although Eruca sativa has a more tender leaf.

Asian Greens. Many Asian greens are best sown as an autumn crop, but there are a number that do well in the spring. Mizuna, leaf mustard, pak choi and tatsoi can be planted in cool soils as early as mid-March. They will grow quickly and in 6-8 weeks can be cut and added to stir-fries and salads. Pak choi and tatsoi can also be started indoors and transplanted into the ground Bok choi in mid-April garden. Photo: J. Padiak
   

Some tips for early spring gardening:

• With a trowel, loosen the soil of the proposed seedbed to speed warming.
• Use row covers, cloches or hot caps to prewarm the soil.
• Use a meat thermometer to take the soil temperature, inserting about 5 cm.
• If you have lots of ground-feeding birds like mourning doves, protect newly planted seeds with cloches to reduce seed predation. Remove cloches when shoots are visible. 
• Plants that are grown indoors need to be ‘hardened off’, the process where plants are introduced to bright sunlight and wind gradually to reduce transplant shock.
  • Take three or four days to harden off plants.
  • On the first day, put the plants in their trays outdoors in protected shade for a few hours, then bring- indoors for the remainder of the day and the night.
  • Next day, increase the length of the outdoor exposure and, again, bring indoors for the night.
  • On the third day, expose to direct sun for several hours and leave overnight, unless especially windy.
  • The plants are ready to go in the soil on the fourth day.

Resources:

• Some Like it Hot – Beverley Wagar – Halton Region Master Gardener
• A Gardener’s Guide to Weather Prediction – Beverley Wagar – Halton Region Master Gardener
• Winter Gardening – Yes You Can – London-Middlesex Master Gardeners
• Cool Season Crops – Peterborough Master Gardeners

Cover Image: A late April snowfall leaves young lettuces unscathed. Note the wide spaces between the plants where a warm weather crop – such as peppers – can be planted for a main crop. Photo: J. Padiak.