Oftentimes, people are hesitant to plant cold-hardy perennials before the last frost date in spring. “What if it snows or freezes?” they worry.
But the truth is, many hardy perennial plants (including shrubs and trees) prefer to be planted when the weather is cooler. Personally, I aim to plant my new perennials as soon as my soil is thawed and workable in spring, which usually happens in March (although my last frost is in June, and it’s not uncommon to continue to get snow through April).
The secret to making sure those plants survive frosty spring conditions?
Ensuring they’ve been hardened off properly to withstand the cold.
You see, hardy plants like to get an early start and if they’ve been acclimatized, they’ll simply shrug off frost.
In fact, if you time it right and plant right before a snowstorm rolls through, you’ll be doing your plants a favor. When new transplants are covered by a blanket of snow, they get the benefit of all that protective insulation on the first clear, cold night after a storm. As the snow melts, it gently waters the transplants and settles the soil around the roots.
(It also doesn’t hurt that snow contains small amounts of atmospheric nitrogen that’s released when the snow melts—a kind of poor man’s fertilizer, if you will.)
So, first step: make sure your new perennials are not only cold-hardy, but also cold-hardened.
If you winter-sowed seeds in jugs outside, then your seedlings have already been exposed to the elements. They won’t need to be hardened off before moving into the garden. (This is assuming you removed the covers from your winter-sowing jugs after the true leaves developed.)
If you’re purchasing transplants from a nursery, ask if the plants were grown in the cold. You don’t want to shock your plants by moving them from a warm greenhouse into cold weather outside without acclimating them first.
New transplants should be gradually exposed to cold weather by sitting outside for an hour or two the first day, then another hour the next day, and so on for the first week. After 7 to 10 days, your plants should be able to spend the entire night outdoors, uncovered. At this point, they can be safely transplanted in the garden.
If I see a hard freeze in the forecast after transplanting (temperatures dropping into the 20s Fahrenheit), I try to cover the plants with frost cloth, an upside-down bucket, or even just a loose layer of straw right on top. If I don’t, the leaves or flowers will usually get nipped by the freeze, but they outgrow the damage quickly as spring gets underway.
Always remember to mulch around your plants to help keep the roots warm. I like to use an organic material like straw, which I layer on lightly in spring. There’s a fine balance between adding just enough mulch to retain warmth and moisture, but not so much that the soil doesn’t have a chance to dry out in early spring.
Related: Straw is not the only material you can use—here are all my favorite kinds of mulch for the yard
So the next time you plant before the last frost and see snow on your new starts, no need to worry—they’re getting exactly what they need to thrive in your garden.
