Protecting Fruit Plants During Frost or Freeze
As a reminder of just how fickle Carolina springs can be, a freeze warning is in effect for much of central North Carolina tonight. Temperatures as low as 28 degrees are expected overnight in the region, with the potential for colder or milder actual lows dependent upon your location. Temperatures below 30 at this point in the season could damage the blossoms and nascent fruit of apples, pears, peaches, plums, blueberries and strawberries. The extent of damage, and what you can do to prevent it, will depend on how cold it actually gets.
For most fruit trees, open blossoms and the phase just after petal shed are the most sensitive to frost or freeze damage. During this time, temperatures of 28 degrees are expected to kill 10% of blossoms. Losing 10% of their potential fruit load could actually be helpful to many fruit trees, which tend to set many more fruits than they can support. The danger comes when temperatures fall any lower – a dip down to 25 degrees could kill up to 90% of blossoms and severely limit this year’s crop.
From a practical standpoint, there is little that can be done to protect fruit tree blossoms. Small trees could be covered with row cover or plastic but covers will need to completely envelop plants and extend fully down to the ground to provide protection.
Blueberries are just starting to bloom in our area, placing them at the most vulnerable stage for frost or freeze damage. Fully and partially open blossoms of rabbiteye blueberries can be damaged at 30 degrees, to the point they cannot be pollinated, and completely killed at 29. Temperatures of 30 degrees can damage small green fruit, resulting in misshapen and undersized berries.
If there are many blossoms on your blueberry bushes and the plants are not too tall, cover them later this evening to prevent loss of early fruits. The goal of covering plants with row cover, old blankets or plastic sheeting is to create a mini-greenhouse that traps in heat from the soil that would otherwise radiate out into the night air. To be effective, covers need to completely encase plants, extend fully to ground level, and be well secured. The good news for blueberry lovers is blueberry bushes don’t open all their blossoms at once. Even if you lose some flowers (and potential fruit) tonight, more flowers should open in the coming weeks.
Strawberry flowers can be damaged or killed at temperatures of 30 degrees or lower. Young green fruit are slightly hardier, withstanding 30 degrees but receiving damage at 28. Because they are lower to ground, strawberries are much easier to protect with covers than blueberries or fruit trees. Be sure to cover your strawberry plants tonight to save any open blossoms and young fruits. As with blueberries, strawberries flower over an extended period so even if you lose some fruit potential tonight you will still get blossoms and berry production in the weeks to come.
Be sure to remove any covers tomorrow morning after temperatures rise above freezing. Fruits that survive tonight’s freeze are still not out of the woods. Overnight lows of 28 degrees are predicted for Saturday night as well. Other than fruit loss, a 28 degree freeze is not expected to cause any long term damage to fruit trees or berry bushes. The same cannot be said for frost sensitive vegetable plants such as tomatoes, peppers, basil, cucumbers and squash. If you have taken the risk of planting early, be sure to these plants are well protected overnight.
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