Frosty fall weather that makes you dig a jacket out of the closet can also be stressful for certain plants in your garden. Temperatures that are too low can kill some plants. While you can't put a jacket on your garden plants or pots of marigolds, you can help them survive cold snaps unscathed. Below you will learn how to provide frost protection for plants, which plants need it and when you should act.
When do we talk about frost?
If there is a frost warning in the fall, this is an advance warning for you to protect annuals and other sensitive plants. You might think that temperatures have to drop to freezing point (0°C), but a frost can occur between 2°C and 0°C. A light frost at the upper end of this temperature range can kill the tops of tender plants while leaving the lower parts green. Hard frost is when temperatures are around 0˚C for a few hours, which is enough to kill all above ground parts.
At temperatures below 0˚ C we speak of frost, which is even more destructive.delicate plants,such as tropical houseplants and geraniums, are killed if the air temperature stays below 0˚C for a few hours. A frost warning often signals the end of the growing season in the fall, as temperatures drop low enough to kill annual plants and initiate dormancy for hardy perennials, trees and shrubs.
Which plants need frost protection?
Typically, annual plants that fruit and flower in high temperatures are the most sensitive to cold weather. You need frost protection for such plants either in spring, when they are still young and tender, or in autumn, if you want to keep them as long as possible before the onset of winter. Many of them come from frost-free, tropical regions of the world. So play it safe and plan for protection if temperatures drop below 4°C.
Perennials, shrubs and trees, on the other hand, can usually withstand a sudden drop in temperature as long as they are healthy and hardy in your region. Some edible plants such as peas, lettuce, onions, cauliflower, broccoli, radishes and cabbage are actually quite resilient. These vegetables thecool seasongenerally withstand temperatures down to -3°C. Even hardier plants such as beets, Brussels sprouts, carrots, cabbage, kale, parsley and spinach can withstand temperatures as low as -6°C. Some cold-tolerant flowers like pansies and thale cress don't mind frosty weather.
At what temperature do plants freeze?
When cold weather comes your way, the first question you will ask is at what temperature plants freeze to death, in other words: How cold is too cold? There is no easy answer to this. Different plants freeze and die at different temperatures. That's why they are classified according to their resilience. Some plants produce special hormones that keep them from freezing, and these plants have lower hardiness (i.e. they can survive colder weather)as plants, which produce less of this hormone.
However, there are also different definitions of survival. A plant may lose all of its foliage during a freeze, and some may regrow from the stems or even the roots. So while the leaves cannot survive a certain temperature, other parts of the plant can.
If you only expect light frost, you may be able to simply cover the plants with a sheet or blanket during frost. This acts like insulation, keeping the warm air out of the ground around the plant. The warmth may be enough to keep a plant from freezing during a short cold snap.
If you theProtect plants from frost, you can cover the sheets or blankets with plastic wrap to keep the heat inside. However, never cover a plant with just plastic, as the plastic can damage the plant. Make sure there is a fabric barrier between the film and the plant.