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.
Temperatures below 40 might damage the leaves, but ``too cold'' comes pretty consistently at 32 degrees. For cold tolerant crops, it is more complicated than it seems. First, different varieties of the same vegetable can be more or less cold hardy.
Cover Plants
Once temperatures drop below about 28°F, covering is typically no longer effective at preventing cold damage. Occasionally even with covering you may still see damage at temperatures above 28°F, especially when the below freezing temperatures are prolonged (5 hours or more).
Covering plant material at temperatures between 39-30 with freeze cloth or covering can be effective. Prolonged exposure at temperatures of 28 degrees and below will notice protection results diminish with each degree dropped.
First, it's good to know which plants are sensitive to temps around 35 or 40 degrees F. These are common tender plants that will need some protection. Hanging baskets: begonias, calibrachoa, gerbera, impatiens, vinca, euphorbia, and scoparia.
So will peppers survive 40 degrees? To sum it up, most peppers won't necessarily DIE from 40˚ F temperatures, but their growth can be stunted, and they may be slow to recover so it's best to keep them warm if possible.
It's sunny again… wait… ), but some vegetables won't be happy (and grow into incredibly prolific tomato producers - yes, I'm talking to you, tomato fanatics) if you don't protect them until night temperatures warm up consistently to 50 degrees and above.
Cucumbers are heat-sensitive and do best in temperatures between 60-90°F (16-32°C). They can tolerate some heat but will become stressed if temperatures exceed 95°F (35°C). Cucumbers can also be damaged by frost and temperatures below 50°F (10°C).
Zucchini is a warm-season crop that cannot tolerate frost or freezing temperatures, so its best to plant your zucchini in the early summer, when temperatures are at least 70 degrees Fahrenheit or more.
When do I know it's safe to bring my plant outside? It's safe to move your plants outside when the outdoor temperatures stay consistently above 50°F. Pay attention to the weather report. If nighttime temperatures are set to fall below 50°F, bring your plants in for the night.
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.
It is best to do this when the earth is moist so that the soil under the plastic is damp and will hold the moisture.
Consult a soil test for fertilizer and liming recommendations. The minimum soil temperature required for germination of zucchini is 60 F, with the optimum range between 70 and 95 F.
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. Gardeners can use a frost date calendar to note their region's average dates of last frost in spring and first frost in fall.
Below 63°F, cucumbers do not grow. In such conditions, plants sit in the soil and become susceptible to damages caused by pests in the soil. With that said, check soil temperatures and be sure they are above 63°F before planting cucumbers.
Seedlings, with their tender new leaves, often give up the ghost when temperatures dip to 32-33°F. Tropical plants have differing low-temperature thresholds. Some keel over when temps fall to 40°F; others crumble at 35°F. Other plants are just hardy by nature and can withstand temperatures as low as 18-20°F.
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. Freeze – A freeze is when the air temperature is 32°F or below.
Most winter squash have pretty good frost tolerance, as long as they don't get exposed to a hard freeze where the temperature might get down to 28° for more than a couple hours. If a heavy frost or freeze is predicted, you can cover your squash with old blankets or a tarp to provide some protection.
No Frost Tolerance
Sweet Corn. Potatoes. Pepper, eggplant. Cucurbits: Cucumbers, summer squash, melons (pumpkins and winter squash may be able to tolerate very light frosts, but it is better to protect them if possible).
At temperatures below 40°F, tomato plants will begin to wilt and brown from chilling injury. At best, the plant will experience stunting, wilting, and pitting of fruit.
H2 Rating - 34 to 41° F (1 to 5 C)
Overall, these annuals are the most delicate of all the hardy annuals - one might call them half-hardy since they are really only hardy into the few temperatures just above freezing. And it's important to NOT let them freeze.
Basil Cold Tolerance
So what temperature is too cold for basil? Basil really begins to suffer when temperatures drop into the 40s, (4 C) and by the first frost, is usually on its last legs.
Daytime temperatures below 65°F can lead to fruit set failure—the pepper equivalent of stage fright. At night, anything under 50°F is an invitation to leaf curl and overall plant stress. It's like the plants are pulling their leaves up to their chins, trying to keep warm.
Tomato plants can suffer from chilling injuries when temperatures are between 0 °C to 5 °C . Pepper plants can also suffer from chilling injury if temperatures stay between 0 to 10 °C (32 to 50 °F ) for a long time. This injury may appear as puckered leaves and stunted growth.
Frost-Tolerant Vegetables
Frost-tolerant veggies can survive several hours in the 28 to 32 degree F. (-2 to 0 C.) range, providing they have been preconditioned to cold weather. Plants exposed to dropping temperatures over the course of several weeks will make biological adaptions.