Cool season vegetables

It’s officially spring and the urge to garden is here!  In the vegetable garden, chives are poking up, signalling the start of a new growing season. Today on Ask a Master Gardener, Susie talks about cool season seeding and transplanting.

Spring chives. Image: Anna Sadura Healey

In our area, April and early May are characterized by cool days and night-time temperatures that can dip below zero, not to mention a chance of snow! Spring days are still quite short, which can be an advantage when planting crops that tend to bolt (go to seed) in the heat and long days of July.

Cool season plants can be either direct seeded into the garden or, in the case of those that benefit from longer growing time, started from seed indoors and transplanted later into their eventual home.

Direct seeding

Hardy cool season crops can be seeded directly into the ground once the soil temperature is about 4°C, or when the ground can be worked. This is generally about 4 weeks before last average frost date.  Susie plans to direct sow her radish, peas and spinach around mid April.

Semi hardy cool season vegetables include beets, Swiss chard, carrots, celeriac and lettuce among others. These can be seeded in early May, about two weeks prior to last frost date. 

Image: Seed Savers Exchange

Tip: to determine the average last frost date in your area, check with Environment Canada. Or simply enter your location into an online calculator. This date is an average based on historical data, so there is still a risk of frost after this date. Watch the forecast and cover any tender plants with a row cover or cloche if frost is predicted.

Seed packages provide a wealth of information including planting instructions (depth, spacing, timing) so refer to these when sowing.

As seeds begin to grow, they may need to be thinned to allow for proper growth. Beet seeds, for example, are actually a small cluster of seeds, appearing to be stuck together. Since each one will develop into an individual plant, some will need to be culled to allow the remaining beets to reach their full size. 

Tip: When thinning (carrots, for example) it is often best to snip unwanted plants at their base, using sharp scissors. This avoids disrupting the roots of the remaining adjacent seedlings.

Hardening off

You’ve nurtured those onion seedlings you started back in February and now, in mid-late April, it is time to transplant them into waiting garden beds. But wait!  They need time to acclimate to the outdoors – unfiltered sunlight, variable temperatures, wind and rain – and so need to be “hardened off”. 

To do this bring your plants outside for an hour or two, increasing the duration outdoors gradually over the next 7-10 days. It is easiest if you place the pots in a tray or bin, since you’ll be carting them outside and then back in at night. And, if they are likely to be nibbled by wildlife, cover the bin with a screen.

How to transplant

Determine when seedlings will move to the garden  – hardy brassicas and onions in mid April, while semi hardy bok choy and cauliflower plants will wait until early May. Warm season crops such as tomatoes and peppers will need to wait until the end of May, as they do not tolerate cold temperatures.

Once you are ready to transplant, assemble the tools you’ll need – trowel, marking twine and spacing stick. Remove any mulch from the garden bed and create a furrow or hole for each plant.  Gently ease seedlings from their pots or if planted in trays, tease individual plants apart. Always handle seedlings by their leaves rather than stems, as the latter are easily damaged. 

Nestle each seedling into the earth, backfilling the hole to the level it was growing in the pot. Tamp down and water well. Note it may be helpful to leave a shallow depression around each plant so that water does not run off.

Tip: Susie uses a homemade spacing stick – a length of bamboo, marked with tape at the intervals she needs. 

Image: Susie Everding

Know the spacing distance, which is based on the size of the plant at maturity. While tiny broccoli seedlings don’t take up much room now, they will need to be 18 inches apart when fully grown.

Finally, cover your new plantings with floating row covers, which provides added protection from dipping nighttime temperatures and from insect pests. The covers can be secured at the edges with smooth stones.

Then, sit back and watch your garden grow!


For more information, explore 1000 Islands Master Gardeners vegetable gardening resource page