Water can make the difference between a summer-planted plant that lives and one that dies. 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.
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.
If your summer is flying by and you haven't gotten to everything on your to do list, it is not too late to plant seeds. July is actually an optimal time as the ground is warm and the daytime and nightime temperatures are warm so your seeds will germinate faster and your plants will grow very well.
When to plant a vegetable garden: it's never too late to start The best time to start a garden is now. It doesn't matter if it's not spring -- even if it's the middle of summer, you can still start a garden, and get a harvest before the snow flies.
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.
Mid-July to the end of August is the ideal time to plant. When choosing your fall tomatoes, make sure you know if you're selecting a Determinate or Indeterminate type. Determinate plants tend to grow to a manageable height and produce most of their fruit at one time.
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.
As a general rule, the smaller, the better. Trees have extensive root systems, and it's almost impossible not to cut them when digging, which leads to transplant shock. You have a better chance with smaller shrubs and ornamental plants.
From spring to fall is the growing season. The most vigorous growth of plants will be in the summer when the sun is up and out the longest. During winter, the sun is neither as high in the sky, nor in the sky for as long as it is in the summer. For your plants, that means less light.
Vegetables that can be planted in August include leafy greens such as lettuce, spinach, collards, kale and mustard. Radishes, turnips, beets and carrots can all be started from seeds in August.
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.
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.
USDA Plant Hardiness Map:
The USDA Plant Hardiness Map divides North America into 11 hardiness zones. Zone 1 is the coldest; zone 11 is the warmest. The USDA Plant Hardiness Zone Map helps gardeners determine which plants are most likely to thrive at a location.
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.
Cucumbers are like the Goldilocks of the garden; they prefer it not too hot, not too cold, but just right. Daytime temperatures should hover between 60-95°F (15-35°C), with the sweet spot around 70-82°F (21-28°C) for those juicy, crunchy fruits.
As a native to the tropics, lantana likes it hot and humid, and grows best in moist, well-draining soil (but can withstand drought conditions). It thrives in the sun, especially afternoon sun, and blooms year-round in tight clusters of red, orange, yellow, pink, or white.
When days hit 85°F to 90°F and nights hover above 75°F, tomato flowers often fail to pollinate, then drop — which in turn puts new fruit production on hold. The longer the heat lasts, the longer those tomato flowers will continue to hit the pause button. In short, hot weather can delay your tomato crop.
June and July Are Still Prime Planting Season. Gardening is an ongoing process, and, while timing is important, don't be overwhelmed by a sense of being too late to plant by some arbitrary date.
Potatoes grow best during cooler weather. Plant potatoes 2-4 weeks before the last frost in the spring, when the soil temperature is at least 40 degrees F. In warm climates, potatoes are planted from January to March and harvested between March and June.