Whether started at home on a sunny windowsill or transported from commercial greenhouses to your local nursery, seedlings that have been nurtured and coddled indoors are in for a shock if they’re planted outside right away. Without being gradually acclimatized to outdoor conditions, young plants can be nipped by frost, pummeled by wind and pelted by rainstorms. With a little patience and care, though, you can toughen them up so they can withstand the weather. Here’s how to do it.
When to start
Knowing when to start moving seedlings outdoors depends on the type of plant as well as local climate conditions. Most annuals and perennial seedlings can be exposed to the outdoors when all danger of frost has passed. This varies from region to region, so consult Environment Canada’s Frost Dates Chart for dates in your area. Some plants, including tomatoes and peppers, prefer warmer conditions, so wait to move these until daytime temperatures are consistently above 18 to 20°C.
Where to site the seedlings
Find a sheltered spot in the yard to set out pots or flats of seedlings. A place under a tree, for example, that’s shaded from the direct rays of the sun and protected from the wind, is ideal. Cold frames or commercially available mini-greenhouses are good options, too. Be sure sites are close to the door so it’s quick and easy to move your seedlings in and out.
On the first day, expose seedlings to the outdoors for only one or two hours before moving them back inside. During the week, gradually increase their exposure by a few hours each day until they remain outdoors all day. During this time, gradually increase their exposure to sun and wind, too, moving them into more open areas day by day, but sheltering them if the weather worsens.
At the end of a week or two, the seedlings should be ready for transplanting to the garden.