The books are right – planting in the summer when it is hot and dry is not the best time to move new plants into or around the garden. During a particularly bad heat wave it can be hard enough to keep the soil hydrated, let alone provide ample moisture for plants that are establishing new roots.
The general answer is around 90 degrees F, with some exceptions to the rule. This means that when temps rise above 90 and remain there for a lengthy spell: Leaves wilt. Water evaporates into the atmosphere more quickly in high heat, draining a plant's reserves.
Planting native plants in the summer heat can put a lot of stress on a young or newly planted plant and natives are no exception. Summer heat can cause wilting and permanent damage to the plant, especially if they are in direct sunlight or not receiving adequate hydration.
Most summers can be warm, but abnormally high temperatures can stress plants, resulting in sunburn, wilting, and even death. Plants in containers are more vulnerable to extreme heat and weather because the air temperatures can “fry” the roots and tops of plants.
During extremely hot weather (daytime temperatures above 90F and nighttime temperatures above 70F), try to water daily or every other day. In a 10x10-foot garden, this would mean giving your plants 8 to 9 gallons of water each day.
While most of our garden plants need at least 6 hours of full sun to be productive, too much sun, especially when combined with too much heat, can be too much for plants to bear. Problems arise especially when temperatures are over 85 to 90 degrees F.
Most of these are fall and winter vegetables (root crops, salad and cooking greens, broccoli, cabbage, etc), but you can still plant a few fast-growing summer crops like green beans, summer squash, and cucumbers – depending on your climate.
Even in the July heat there are still some great crops that can be planted that will keep your garden pumping out vegetables well into the fall. Listed below are flower, vegetable and herb varieties that are great to start planting in July based on the Hardiness Zone that you live in.
Ideally, the time to move most perennials is either spring or early fall. The hot, generally dry weather of summer is about the worst time of year to move any plant.
The general rule of thumb is that most plants freeze when temperatures remain at 28°F for five hours. Of course, there are exceptions to this rule. 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.
It can take anywhere from a couple of days to a couple of months for stressed plants to recover. Recovery time depends on the amount of damage that the heat caused to the plant. If a stressed plant is completely neglected during a heatwave, it can take several months or even be impossible to revive it.
Most plants grow best in temperatures ranging from 59°–86°F. When temperatures above 90°F are sustained for long periods, plant growth is slowed, and some plants begin to show signs of stress.
Ideally, transplant your flowers, ornamental grasses, and foliage plants on a cloudy, overcast day that isn't too windy. Planting early in the morning before the sun heats up the soil will produce the best results.
Summer isn't as ideal of a time to plant as spring or early fall, but with a few precautions, most plants will do fine. Peak sunlight and searing heat are added stressors on young plants with small roots, not to mention, summer soil tends to be drier.
You can plant in the hot, dry summer, but fall is really a great time to plant large shrubs and trees, as they bulk up their existing root systems over winter, letting them drink more water.
It's just too hot to plant, for both me as a person and also for the plants. Anything over 85 degrees is too much.
Most plants shut down during extreme heat, so if it is over 100 degrees, it may be best to wait to water even if your plant is stressed. Throw a damp sheet over it, or mist it lightly to bring the temperature down. Mist leaves with a spray nozzle to cool down plant and reduce transpiration.
In hot weather you need to water in the mornings when it is cooler. This will allow more water to reach the root system before it evaporates in the heat. There may be times when you cannot schedule watering in the morning. In this case, water the plants in the late evening before bed.
Even if the air is hot your plants will be happier without the hot sun frying them to a crisp. Plant early in the morning or at night just before or after the sun comes up. The air tends to be cooler and the sun less intense. Whatever you do, avoid the midday sun, which is the hottest and highest in the sky.
Some signs of heat related stress on plants include: leaf scorch, leaf rolling, wilting, blossom/fruit drop, sunscald, blossom end rot, and other variable conditions that could be brought on by secondary pathogens. Heat stress adversely affects plant metabolism, disrupting their vital biochemical processes.
When a plant gets too much direct light, the leaves become pale, sometimes burn, turn brown and die.