Avoid watering when temperatures are below 40°F or when sustained freezing temperatures are expected within 24 hours as this water will freeze and not be available to the plants.
Flowers also need a steady flow of moisture right up until the ground freezes in late autumn. 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.
Better not. In winter most plants have lost their leaves which means they are inactive. Those who haven't lost their leaves are inactive too. Not only that, there is hardly any evaporation so the soil at the depth of the roots isn't dry. By watering you can do harm while there is no use for the water you give.
The best time to water outdoor plants is in the morning when temperatures are usually cooler. This gives the plants time to absorb the water so they can get through a long, hot day. The second-best time is late in the afternoon or early in the evening. Try not to water at night.
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. Be sure you know this before you plant.
Avoid watering when temperatures are below 40°F or when sustained freezing temperatures are expected within 24 hours as this water will freeze and not be available to the plants.
There are, of course, many variables that can affect winter hardiness in a plant, but in general, my rule of thumb is as long as the mercury stays in the 20's at night and rises above freezing during the day, our plants should be just fine.
Trees, shrubs, perennials and most of the “permanent landscape” are fine when gardeners go away for a week or two of summer vacation. Potted plants and hanging baskets are more of a concern. These can wilt after just a day or two without water, especially in a hot, sunny spot and especially when recently planted.
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.
When watering your plants, it is essential to use water at the right temperature. This is because the roots of your plants are very sensitive to extremes of temperature. Using water that is too hot or too cold can put your plant under stress and cause damage.
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.
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.
If it is not going to rain before the freezing temperatures arrive, you should water plants thoroughly. This is because moist ground stays warmer than dry ground. Watering the night before the freeze arrives will insulate the root structure of the grass and plants, decreasing the potential for cold injury.
As a rule of thumb, water when the soil is dry to the touch, the temperature is not below 40 degrees F. (4 C.) and, if possible, when the wind isn't blowing. Drying winds may carry off much of the water you're trying to apply to the roots of your beloved plants.
Provide Slow, Deep Watering
If you are unsure how long to water new plants, aim for 30-60 seconds for small plants – longer for larger plants while moving the hose to a few locations around the plant. Avoid watering when the soil feels moist. The earth must be allowed to dry out between watering.
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.
The evening
Don't do that. Evenings are best avoided because of evaporation and transpiration (I think of transpiration like a plant breathing). Around 99% of water a plant takes up does NOT stay in the plant. Tiny pore-like holes on leaves, called stomata, take in carbon dioxide and 'breathe out' oxygen and water.
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.
Avoid creating a routine of watering at the same time every day or every week. Instead, get in the habit of paying attention to the soil and the weather so you can water when the plants really need it. Containers need frequent watering.
“Most plants will typically be fine if you're gone a week, but some may start to suffer if they go without water for two weeks,” says Justin Hancock, Costa Farms horticulturist.
If you have left your plant without water for a week, then bottom watering is the best way to revive it.
Temperatures below 50°F may stunt their growth for a few weeks, and temperatures below 35° may cause some leaf damage. Freezing temperatures will kill the leaves of most houseplants completely, but the roots typically survive if it was only a short exposure.
Choose days when no snow is on the ground and the soil isn't frozen. In cold weather, water should be trickled slowly into the soil. Water only when air temperatures are above 40 degrees F. Apply water at mid-day so there is time to soak in before possible freezing at night.
Light freeze - 29° to 32° Fahrenheit will kill tender plants. Moderate freeze - 25° to 28° Fahrenheit is widely destructive to most vegetation. Severe or hard freeze - 25° Fahrenheit and colder causes heavy damage to most plants.