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.
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.
40F won't hurt any of those plants but if the soil gets too cold they can all be affected. So if it's me I cover if I think the soil might get too cold too long. Most warm season crops I like to maintain 60F soil temp minimum.
Each plant has a different threshold when it comes to dealing with the cold. Some plants can survive outside even when temperatures hit freezing. Others need to be brought indoors when temperatures reach the mid-40s.
Before the Risk of Frostbite: If you're growing pepper varieties that are especially sensitive to cold, consider bringing them indoors even earlier, when nighttime temperatures are consistently above 55°F. This will help prevent any potential damage to the plants.
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.
In the case of peppers, the ideal daytime temperature is 21-26°C (70-80°F). The ideal nighttime temperature is 18-21°C (65-70°F). Of course, these ranges may vary, depending on the pepper varieties you grow. Pepper plants may still grow outside of the ideal temperature range.
So when temperatures start dipping below 50º F, leave the tomatoes on the vine if warmer days and nights are forecast. But if temperatures have started on a steady downward slide, go ahead and pick the mature green tomatoes and bring them indoors.
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).
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.
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.
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).
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.
Know Temps for Fruit All Summer
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.
Set out plants a week or two after your last frost, when the weather is settled and warm. While cool weather reigns, keep seedlings indoors at night, and move them to a protected sunny spot outdoors during the day.
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. To find the threshold for your plants, search garden books and online resources.
Basil is an extreme example of this, as the leaves can turn black when the temperatures dip into the 40s. Other plants are a little more tolerant, and warm temperatures following a short cold exposure can reverse some of the injury.
Temperatures below 60°F at night will also result in blossom drop. At temperatures below 40°F, peppers may show some chilling injury. A shortage of water at bloom time can also result in blossom drop or failure to set fruit.
Tomatoes are fine with 45+ F. Peppers at that temperature refused to grow or get permanently stunted. They need 50-55+ F.
Don't put tender seedlings outdoors on windy days or when temperatures are below 45° F. Even cold-hardy plants will be hurt if exposed to freezing temperatures before they are hardened. Reduce the frequency of watering to slow plant growth, but don't allow plants to wilt.
The morning sun is favorable because it is less intense than the afternoon sun. If your plant receives at least 6-12 hours of sunlight, it will have more energy to grow tall and strong. If your plant only receives 6 hours or less of sunlight, it will likely have a smaller harvest.
For pepper plants, a balanced fertilizer with equal proportions of Nitrogen (N), Phosphorus (P), and Potassium (K) is recommended. However, pepper plants respond positively to higher nitrogen concentrations during the flowering stage.