False spring occurs during winter when the weather becomes unusually warm before getting very cold again. The air is soft, warm and moist, the birds are singing. Why it must be spring! Not. Though all the signs of spring are with us, one critical ingredient of spring — the element that gives spring its legitimacy — is nowhere in sight.
It can look, smell and feel like spring, but if it’s not close enough to the last average frost date, don’t get fooled into believing it’s spring. All of my gardening friends are feeling the pull to get out into the garden and plant. But take heed – the average last frost date is not even close. We are still months away. A key point to consider is frost. Technically speaking, frost forms on solid objects when the water vapor in the atmosphere changes from its vapor phase to small ice crystals. Frost is not frozen dew.
If you see frost than you know that the temperature of the object it is on reached 32°F or lower. However, the air temperature, measured a few feet above the ground of this object, is likely several degrees higher. In contrast, not every air temperature recorded at or below 32°F means frost formed on solid objects in the area. In spite of this, the average date of the last spring air temperature of 32°F has traditionally been called the last frost date. For Sanford, here in Lee County the average last spring frost date and its standard deviation is April 19, give or take 12 days.
This month last year our temperatures ranged from the 40s to over 80°F. Then in March, there were quite a few days that reached down into the 20s, fatally injuring fruit blooms. The three-month outlook from the National Weather Service looks eerily familiar for this year. So if you’re thinking that all this warm weather means that winter is over and no more frost – well maybe. But I wouldn’t “bet the farm” on it – nor the garden.
To put this in perspective, plants naturally get prepared for cold. Internal environmental monitors signal to get ready for winter. These can include producing antifreeze-like compounds, changing “freezable” carbohydrates in their stems to freeze-resistant sugars, and the making the vulnerable tender new growth is put on hold. But as a warm spell like this continues, plants’ different environmental triggers can come into play putting on flowers and new growth. Even though you may be itching to get your pruning tools into action, keep in mind that pruning also stimulates new growth. Encourage the production of tender and vulnerable new growth now, before the last frost date is a risky business.
Right now this looks like a false spring. The longer a false spring lasts, expect even mild subsequent frosts to cause damage. Consider putting up your cutting tools for now and draft your garden plan instead. Unless you are working on muscadines or blueberries, postpone pruning until later in spring. For more information about what low-temperature protection methods are useful to protect take a look at Frost/Freeze Protection for Horticultural Crops.
Minda Daughtry is Horticulture Agent for North Carolina Cooperative Extension in Lee County.