On a mid-March morning one year, had you been at my home, you would have found me in my blueberry bush bed, taking giant sheets off my blueberry bushes.
My fingertips grazed the white blossoms to see if the freezing temperatures from the past two nights had damaged them. Since each of those blossoms is a future blueberry, a late freeze had threatened to potentially ruin my blueberry crop.
The week before, I received an alert that our area would be under a freeze warning. Before I became a gardener, I would ignore such warnings. But now that I have plants in the ground and blueberry bushes in bloom, it matters very much how cold the early morning temperatures get.
But until recently, I couldn’t tell you the difference between a frost and a freeze, nor did I know which plants it would affect and what to do. For the beginning gardener, this is a common concern. Let’s break it down so you can protect your garden when a late freeze or frost threatens your tender new growth.
Difference between a Frost and a Freeze
A frost occurs when early morning temperatures dip below 40 degrees, the sky is clear, and the wind is calm. The warmer ground gives off heat, causing cooler air to dip near ground level. Moisture around the plants, under similar circumstances as the formation of dew, settle on the leaves and freeze.
A freeze, on the other hand, occurs when the air temperature is 32 degrees or lower for a period of a few hours, regardless of whether frost develops.
The Predicted Frost that Became a Freeze
One of my first years of gardening, a frost warning was issued in late April (uncommon in our area). I rushed to cover my tender summer crops — tomatoes, basil, cucumbers, and beans — and my blueberries, which had just blossomed due to the late arrival of warm temperatures. I left my potatoes alone because I thought they tolerated cold.
The next day I walked out into my garden and took the covers off my crops. My summer vegetables were fine. The blueberry blossoms that were covered were fine, though the few I wasn’t able to cover had turned brown. But I was most surprised when I looked at my potato vines. They were wilted and dark. At first confused, I realized what happened. The temperatures dipped below expectations and we had a freeze instead of a frost. The freeze damaged the tissues of my potato leaves and killed them. Thankfully, within a week the potatoes began re-growing their leaves.
Plants that Die in a Frost
Generally speaking, summer crops cannot tolerate a frost: tomatoes, beans, cucumbers, melons, squash, peppers, black-eyed peas, and basil. When you expect temperatures to dip below 40 with a calm wind, you must cover these crops. That’s why it’s best to wait to plant these crops until the danger of frost has passed. Not only is it not good for the plants, even if they’re covered, but covering them can be a pain.
Plants that Die in a Freeze
Generally speaking, all summer crops plus some spring crops are vulnerable to freezes: cabbage, broccoli, lettuce, and peas, in addition to the summer crops. Also, the blossoms of perennial berry bushes — which will eventually produce the berries — may not tolerate a freeze. The plant itself will survive, but each blossom that dies is a berry that won’t develop.
What to do When a Frost or Freeze Threatens
The most important action you can take to protect your vulnerable crops from a frost or a freeze is to cover them. For young seedlings, an upside down pot with a rock on top (to prevent it from blowing away) is sufficient. For plants that are too tall for upside down pots, try sticking a tomato cage around it and covering it with a blanket, towel, or sheet. (Don’t lay them directly on the plant or the weight of it — especially if a frost occurs — will be too much for the stems to bear up under.)
For my blueberries those cold nights in March, I took light sheets and wrapped them mummy-style, as suggested by my husband. Though a couple of branches broke from the weight, for the most part the branches withstood the wrapping. I was willing to sacrifice a few young branch tips for the good of the crop.
Be sure, the next morning, to uncover the crops as the sun rises and temperatures climb above freezing.
In a perfect spring, temperatures will follow a predictable pattern and you won’t have late frosts or freezes. But you never can predict the swings of Mother Nature, and it’s important to know how to prepare when your littlest plants and buds are vulnerable. W
hat other tips do you have in protecting your crops from unseasonably cold weather in the spring?
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