Ice cold water will cause root shock, which may lead to permanent root damage, leaf drop and other problems. Allow the water to warm to room temperature before watering the plants.
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.
You should water your plants with warm or room temperature water, as it mimics rainfall's natural conditions. If you use water that's too hot, you may boil your roots and damage the helpful microorganisms in your soil. On the other hand, ice cold water is also not advisable as it may shock the roots.
I did some research and found out that houseplants need to be taken indoors before overnight temperatures dip below 45 degrees. Most tropical plants suffer harm from temperatures below 40 degrees.
As cold as 57°F may feel to us, it's okay for general use. It's water below 50° that's trouble. * Then, it's trouble for those few tropical species we grow indoors which may develop leaf spots or stunted root tips from cold watering.
In general, the water used to feed plants should be kept around room temperature; ideally, use water anywhere between 60 degrees to 70 degrees Fahrenheit. However, 68 degrees Fahrenheit is the perfect temperature for most plants because it promotes oxygen uptake and root efficiency.
Fortunately, most tap water has low levels of chlorine that won't be directly detrimental to your plants. But if you're still concerned, simply check the smell of your tap water. If you can smell chlorine, it likely has unusually high chlorine levels.
As gardeners, our frost dates are based on 32 degrees Fahrenheit (0 degrees Celsius) to avoid the risk of any plant death. However, know that even if air temperatures are as high as 38°F, frosts may occur on the ground and on plants. It's better to protect plants just in case!
Signs Your Plants May Be Too Cold
The leaves brown and fall off. If your plant is too cold, it may begin to die, and its leaves will brown and fall off. The leaves turn yellow.
For many plants, temperatures below 50°F can cause problems. Adjust thermostats to cater to your comfort, but remember your plants need some consideration. Avoid placing plants near cold drafts or heat sources. Keep plants several inches away from exterior windows.
Best Water for Houseplants
Most tap water should be fine for houseplants unless it is softened because softened water contains salts that can build up in the soil over time and cause problems. Chlorinated water is also safe for most houseplants, but if you have a filtration system, that's much better for your plants.
Along the way, they debunk one myth after another. One of the most surprising findings is that freshly picked flowers should be placed in cold water, not warm. With a few exceptions, warm temperatures rob the flower of food and water, often resulting in dehydration.
The ideal water temperature for watering plants is between 62-72°F. Within this range, the water is not too cold and can still hold a good amount of dissolved oxygen. When discussing water temperature for plants, it is important to understand dissolved oxygen.
The second-best time is late in the afternoon or early in the evening. Try not to water at night. Night-time watering is not ideal because your plants' leaves may not be able to dry off as quickly as other times of day. Wet leaves are more susceptible to diseases.
Plants do best when watered deeply about three times a week, factoring in the rain. If the plants are seedlings, water them twice a day until established.
It can be tricky choosing when is the best time to water plants in winter. Avoid watering early in the morning or late at night, keeping to the middle of the day wherever possible as the soil around plants should be dry 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.
Because the enzymes driving biochemical reactions don't function well in winter, dipping temperatures and lack of sunlight slows plants' metabolism. Photosynthesis and respiration decelerate, and growth halts.
It should be noted that some house plants are more vulnerable to cold damage than others and when the thermometer dips – they can suffer. Some of those more sensitive to cold temperatures: Orchids (Phaleanopsis sp.), Mandevilla, Bougainvillea, Oriental Hibiscus, and Poinsettia.
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.
Once temperatures drop below 40°F, you may want to start covering your plants with a frost blanket depending on what you're growing, which we'll get into in just a bit. Freeze – A freeze is when the air temperature is 32°F or below.
If you're wondering at what temperature threshold you should be bringing your plants, there's a short answer: when nighttime temperatures reach 45 degrees (F), it's time to bring your plants indoors.
Wetting leaves.
Plants get their moisture through their roots, not their leaves. Direct watering to the soil surface and avoid wetting leaves because water helps spread some plant diseases. Use a watering wand to reach ground level or a soaker hose or trickle irrigation system to wet the soil rather than the leaves.
Pro: Bottled water can be a great alternative to tap water, if the local water is not safe for plants. If bottled water is the easiest option for you, try to use bottled spring water as it contains natural minerals that help plants grow.
Collected rain is usually naturally slightly acidic, so it can help flush away the build up of accumulated substances from alkali tap water deposits in your potting soil. I just set a bucket out in my yard to collect rainwater, fresh from the sky. Fresh bucket-collected rainwater is tops in purity for plant watering.