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.
So, how hot IS too hot for plants? The general answer is around 90 degrees F, with some exceptions to the rule.
Wind down the water as temperatures begin to drop below 40 degrees. Most summer annual plants will freeze and die with the first or second hard frost. As always, irrigate your perennials and annuals in the morning when you can!
With proper care and attention, you can enjoy beautiful, flourishing flowerbeds even during scorching 100+ degree heat. Remember to water wisely, use mulch, select heat-tolerant plants, provide shade, and perform regular maintenance.
If it's 70-80 degrees outside try watering 2-3 times a week. During the spring your lawn will be fairly easy to manage so you don't have to water all the time. In the blazing summer, when temperatures are between 90-100+, try watering 3-4 times a week.
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.
Don't Water at Mid-Day in the Sun. "Don't Water Your Plants in the Middle of the Day!" How many times have you heard that? "Only water your plants in the early mornings or late evenings." THE CHALLENGE: That's easy to say, but not always easy to do.
Run your sink into a watering can, cup, or bucket, and let it sit for a good 24 hours. This will allow chemicals like chlorine and fluoride the time to evaporate from the water. We like to have a full watering can ready to go with still water so that if our soil seems dry, we can water our plant without waiting a day.
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.
Temperatures of 104 degrees Fahrenheit for four hours will kill the root tips of most plants.
Above 104°F, many plants will survive but will show different signs of heat stress depending on plant type, maturity of the plant and factors that often come with high temperatures, such as drought or wind. Extreme air and soil temperatures slow down chemical activity and growth in plants.
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.
It is so hot out there!
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.
Containers need frequent watering.
Because there is little soil in a pot to hold water, container plants need to be watered more frequently than plants in the ground. In hot weather, they may need to be watered daily.
Mornings and evenings are excellent times to water gardens when using a drip irrigation system or soaker hose. Watering in the evening isn't a problem as these methods don't wet plant foliage.
Morning watering is actually preferable to evening watering as the plant has time to dry before the sun goes down. At night, water tends to rest in the soil, around the roots, and on the foliage, which encourages rot, fungal growth, and insects.
If a plant is watered so much that water is coming out of the bottom of a drainage hole - that means the soil is more than fully saturated and for many plants this means - they have been overwatered! Many plants do not need all the water that remains in that planter and this can quickly lead to root rot.
Boiling water for 15 minutes removes chlorine and certain contaminants from tap water. Let stand to room temperature before watering your plants. Hot water under 120°F is generally safe for most plants. Above 120°F, water can burn a plant's cell walls, causing them to wilt and then die.
Watering plants in the heat of the day is not ideal, but not because the water and sun together will scorch the leaves. The main reason not to water when the sun is high in the sky and temperatures soar is because of evaporation.
The best way to tell if your plants need water is to stick your finger about an inch into the potting mix—if it feels dry, break out the watering can. If you detect dampness, check back again in a day or two. For smaller houseplants, you can also pick up the whole container. If it feels light for its size, add water.
This depends on the plant types, garden light conditions, and weather. Plants in shaded areas may last longer without water compared to those in full sun. Container and window box plants can dry out in a day, whereas many houseplants can manage with one watering per week or less.
The root of the trick's protection is a concept called "latent heat of fusion." When the water on the plant starts to freeze, it releases heat (a necessary process to turn water into ice), and that heat helps protect the plant.
Though some species are more cold tolerant than others, most will perish or enter diapause once temperatures fall below 32°F, which answers the question, “how cold is too cold for mosquitoes?”
A moderate frost, with temperatures ranging from about 28°F to 32°F, necessitates a bit more precaution. In addition to tucking your plants in well with some frost cloth or cover, it's also a good idea to water your plants the evening before frost is expected to hit.