Frost Dates and Pushing the Limits

By Chris Freeburn, Master Gardener

Many of us have grown up with the rule of planting the vegetable garden on Victoria Day (May 24th) long weekend. With the changing weather, hardier plants and stretching the limits, we have realized that many plants can go into the ground well before that date, while others do need the soil to be warmer.spinach-3368254_640

Cool Weather Crops

Cold weather crops like lettuce, spinach, pea, beet and carrot seeds can be planted well before that mystical date. They actually like a cooler temperature to germinate. If you plant them the first week of May, you should have sprouts coming up by the time you plant other seeds.

Warm Weather Crops

Ground temperatures need to be warm for beans and cucurbits such as squash, pumpkin, cucumber and zucchini. Mid May to early June is probably best for putting actual plants in the ground, if you are in an area that does not get frost. Check your weather network for overnight lows. If the temperatures drop and the night sky is clear, chances of frost are better than on a cloudy night. If the air is still, colder air will settle close to the ground and damage plants. If your property is on a slope or higher ground, the cold air will settle around you in the valleys and you may not be touched by a light frost. Being closer to water often draws the cooler air away. If you have planted tomatoes and peppers and there is a frost warning, go out and cover your tender plants with sheets.

Basil and cilantro do not like cool nights, so leave these tender herbs in pots to bring in overnight or do not plant until June.

Annuals

pansy-3373732_640Some annuals such as pansies, dusty miller and english daisies are cold tolerant while others like potato vine and impatiens do not like temperature changes. Do not plant the latter 2 choices into the ground until all danger of frost has passed and the soil temperature has warmed. If the nights temperatures are dropping, bring your pots into your garage or cover with an old sheet to protect.

Perennials

Perennials have survived the winter frozen in the ground so a bit of frost will not hurt them. If you are buying perennials that have been grown and forced in a hot greenhouse, they will need to be pampered by slowly introducing them to seasonal temperatures. This is called hardening off. To harden off any plants that have been living in a warm greenhouse, put them outside in a shady area, protected from the wind for a few hours over several days. Bring them back into the warmth of your home or heated garage for the night. Increase the number of hours they are outside each day, until they are used to the outside temperatures.

According to the Farmers Almanac, the last frost date for Peterborough is May 14th, however the full moon is on the 28th. If the night of the full moon is clear and cool, we could see frost. Beware!

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