Temperatures below 32 degrees can freeze the leaf tissue of cold-wimpy plants and turn them to mush after just a few hours. Some of the most tender annuals and veggies might not die but suffer cold-induced setbacks even when overnight lows dip below 40.
Generally, the ideal temperatures for vegetable plant growth are between 40° and 85°F. At warmer temperatures the plant's growth will increase, but this growth may not be sound structural growth. At lower temperatures the plant's growth will slow down or stop altogether.
I did some research and found out that houseplants need to be taken indoors before overnight temperatures dip below 45 degrees. Most tropical plants suffer harm from temperatures below 40 degrees.
If you're wondering at what temperature threshold you should be bringing your plants, there's a short answer: when nighttime temperatures reach 45 degrees (F), it's time to bring your plants indoors.
A light freeze is considered 28°-32°F, and a hard freeze below 28°F. However, any temperature below 25°F is dangerous territory for most vegetable plants.
Ideal temperature range for growth and fruiting is about 65° to 75°F. Zucchini withstands temperatures up to 100°F, but growth and fruiting may be diminished at temperatures above 85°F, and flowers may drop at high temperatures. Most varieties grow slowly or not at all at temperatures below 60°F.
If it stays cold for more than one night, can I keep my plants covered, or should I remove the coverings at some point? A. Our recommendation would be to remove the cold protection covering once temperatures are above 32 degrees.
Most cucumber varieties are extremely tender and cold sensitive. Generally they will be harmed or killed by frost. Many varieties grow slowly or not at all at temperatures below 55°F. Plants may become stressed and fruit quality diminish during periods of cool weather below 50°F.
And any time the nighttime temps fall below 33°F, you can expect damage to the leaves and the plants may die. Should the freeze grow colder still, with temperature plummeting below 28°F, it's unlikely you can save the plant even using a row cover or plastic to protect them.
Temperatures between 38ºF and 55ºF won't kill tomato plants, but keeping them covered for an extended amount of time can. Remove coverings in the morning or once temperatures rise over 50ºF to give them extra light and warmth.
Tomatoes don't thrive well in low temperatures, and the fruit is vulnerable to diseases in cold seasons. You should cover your plants when temperatures get to 40 to 50 degrees to protect them. Tomatoes don't do well in the cold, so covering them when there is frost keeps them warm and ensures continued growth.
So even though the weather forecaster isn't predicting a freeze, once temperatures start to drop below 40°F you need to be aware. Once temperatures drop below 40°F, you may want to start covering your plants with a frost blanket depending on what you're growing, which we'll get into in just a bit.
Hardy plants can be hardened off when the outside temperature is consistently above 40° F. Half-Hardy plants may be hardened off at 45° F.
Semi-hardy cool-season crops (beets, carrots, Swiss chard, lettuce, cauliflower, potatoes, parsley) grow in minimum daytime temperatures of 40 degrees and higher. They cannot withstand hard frost without some kind of covering or protection.
Freeze Warning - This is issued when there is at least an 80% chance that the temperature will hit 32 degrees Fahrenheit or lower. Light freeze - 29° to 32° Fahrenheit will kill tender plants. Moderate freeze - 25° to 28° Fahrenheit is widely destructive to most vegetation.
Know Temps for Fruit All Summer
If you're the kind of gardener that keeps records, make note of the date and soil temperature for future plantings. Another temperature to keep in mind: tomato plants will not survive in temperatures below 35 degrees Fahrenheit, and will not thrive at temperatures below 50 degrees.
Cucumber beetles feast on the foliage of cucumber plants, leaving holes across leaves and flowers. In extreme cases, these yellow beetles begin to nibble on the plant stems and, eventually, the vegetables we love.
Zucchini does not tolerate frost or cold temperatures.1 So you won't gain anything from planting too early. Even if fruits form during cold weather, they will have pitted skin from chilling injuries. Thus, you should wait until at least mid-spring to plant when the soil warms, depending on your climate.
Provide Heat with Water Jugs
Fill up several one-gallon jugs with water and screw on the cap. Nestle these jugs into the soil next to the tomato plants, in a spot where they will warm up in the sunshine. At dusk, cover the plants with your frost covers. The water jugs will slowly emit heat throughout the evening.
Pepper plants will tolerate temperatures as low as 55 degrees Fahrenheit but may start to wilt and die in temperatures below that. The mature plants can thrive at 80 degrees Fahrenheit at maximum durability, while the best temperature is between 50 to 60 degrees Fahrenheit.
Temperature. The ideal temperature range for growing green beans is between 65-85°F. They are not tolerant of extreme temperatures, either heat or cold. When it falls below that, growth will slow, and frost will eventually kill the plant.
From that experience, I've found the best frost protection for your outdoor plants is either free or cheap. Cardboard boxes and brown grocery sacks make perfect frost cover and at the end of the season can be recycled. I keep various boxes on the patio and when frost is forecast simply put one over the plant.
Thoroughly Water plants if it's not going to rain before the freezing temperatures arrive. It may sound illogical. However, a moist ground stays warmer than dry soil. Watering the night before the freeze comes will insulate the root structure of the grass and plants and decreases the potential for cold injury.
For many plants, temperatures below 50°F can cause problems. Adjust thermostats to cater to your comfort, but remember your plants need some consideration. Avoid placing plants near cold drafts or heat sources. Keep plants several inches away from exterior windows.