It was cold last night, and I had a space heater on high in my greenhouse. The temperature was below 60º, not warm enough for them to grow, but certainly warm enough to keep them happy. Today I am taking steps protecting plants in a freeze.
We, here in the Midwest, have weather predicted for possible frost the next few nights. Unexpected freezes can devastate landscapes and gardens. It leaves me thinking about how to protect our plants from freezing and what is the best way to cover and keep plants from freezing.
At What Temperature Do Plants Freeze?
When cold weather comes your way, your first thought will be at what temperature do plants freeze, in other words, how cold is too cold? There is no easy answer to this.
Different plants freeze and die at different temperatures. That is why they are given a hardiness rating.
A Light frost is when…
the air has dropped below freezing but the ground has not.
A hard frost….
is a frost where both the air and the ground freeze.
COLD TOLERANT ANNUALS (hardy annuals)
Calendula, Dianthus, Forget Me Not, Pansy, Snapdragon, Stock, Sweet Alyssum, Sweet Peas and Viola
COLD TOLERANT VEGETABLES
Broccoli, Brussels Sprouts, Cabbage, Cauliflower, Lettuce, Peas, Radish, Spinach
Note: An annual plant may lose all of it’s leaves during a cold spell, but this does not necessarily mean it died. Wait to see if it rebuds. But if there was a heavy frost…
an annual will typically not survive. Don’t worry about you perennials, they’ll be fine.
HOW TO PROTECT PLANT FROM FREEZING?
If you are only expecting a light freeze cover them with a sheet or a blanket. It will act like insulation, keeping warm air from the ground around the plant. The warmth may be enough to keep a plant from freezing during a short cold snap.
For added protection place plastic over the sheets or blankets to help keep warmth in. Never cover a plant with just plastic, since the plastic will damage the plant. Make sure that a cloth barrier is between the plastic and the plant.
*****Be sure to remove the sheets and blanket and plastic first thing in the morning after an overnight cold snap. If you don’t condensation can build up and freeze again under the covering, which will damage the plant.
WHAT ABOUT LONGER OR DEEPER FREEZES?
In longer and deeper freezes you may have to sacrifice all or part of the plant to keep the roots alive. Heavily mulch the roots of the plant with either wood mulch or hay. For added protection, you can nestle gallon jugs of warm water into the mulch each night. This will help drive off some of the cold that can kill the roots.
If you have time before a freeze happens, create insulation barriers around a plant. If you can, tie the plants up and drive stakes that are as tall as the plant into the ground around the plant. Next wrap the stakes in burlap so that the plant appears to be fenced in. Stuff the inside of this fence with hay or leaves.
TIP: before a freeze water your plants (not leaves or stems), which helps retain heat (takes longer to freeze) helping to keep the soil from freezing protecting the roots and lower stems.
I hope these tips help keep you plants safe during unexpected cold spells.
Today I’m spending time preparing my annuals from a possible frost. Hubs and I are also layering drop cloth tarps and old blankets over the greenhouse. In addition we are hanging several shop lights for another heat source beside the space heater that is on high!
Wishing you safe plants….and future blooms!