What Temperature Is Too Cold To Water Plants? Here Is Why

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Watering plants is one of the most important parts of gardening, but unfortunately, it’s not always as simple as it sounds. This is especially true when the weather is cold because the process can become much more complex when temperatures are involved. What temperature is too cold to water plants, and why?

Below a temperature of 40°F (4.4°C) is too cold to water outdoor plants. This is because anything under this temperature is too close to the freezing point of water, which is 32° F (0°C). If the water freezes, your plants cannot access it. Frost is also damaging to plants.

The rest of this article will discuss everything you need to know about watering plants in cold temperatures and why certain temperatures are too cold. Read on to learn more about my favorite tips for watering your plants when it’s cold. 

Watering Plants: How Cold Is Too Cold?

In regions where the climate is cold during the majority of winter, it’s essential to take necessary precautions to protect the plants in your garden. So, how cold is too cold to water your plants?

If the temperature outside is just above or below freezing, then this is too cold to water your plants. Watering your plants when it’s freezing outside can cause too much frost, damaging your plants and even killing them. 

You can still complete landscaping projects during winter, but it’s always important to be extra careful. A good rule of thumb is to not water your outdoor plants when temperatures are 40°F (4.4°C) or below, especially not when it’s below freezing. This is to avoid excess frost exposure.

However, it’s also important to note that this varies from region to region and plant to plant. No one temperature is suitable for watering every plant, and every area has its own climate.

Therefore, it’s essential to research your plants’ species and the weather patterns in your area to ensure they get the care they need.

Why Are Cold Temperatures Bad for Plants?

So we’ve established that cold environments are generally not great for plant growth. But why are cold temperatures so bad for plants, exactly? 

Cold temperatures are bad for plants because it can cause the cells inside them to freeze. When plant cells freeze, the cell walls will break, and they will no longer be able to transport water and nutrients throughout the plant and its internal systems, which can kill the plant.

According to Penn State, the volume of water actually expands by 9% when it freezes. This expansion can lead to plant cell breakage and, ultimately, the death of your plants.

This is why it’s vital to prevent plant frost as much as possible. But how exactly can you go about doing this?

How Can You Prevent Plant Frost?

As previously discussed, watering your plants when it’s too cold outside can lead to excess frost. However, even when you don’t water your plants in freezing temperatures, frost can still occur due to natural moisture levels in your environment’s air. Are there ways to prevent plant frost?

You can prevent plant frost by setting up winter irrigation systems, providing your plants with shelter from the elements, investing in heaters, and watering your plants in the morning before night frost kicks in.

The following section will expand upon these tips and provide explanations to better understand frost prevention. Let’s explore each of these points in further detail.

Winter Irrigation Systems

Setting up an overhead irrigation system that will spray your plants with water is an excellent way to prevent excess frost damage to your outdoor plants. It’s also more cost-effective than pricey heating systems.

Spraying your plants is different from watering the root system. Spraying using an overhead irrigation system is very effective for frost prevention because it distributes the water evenly. On the other hand, watering the root system targets one area, which can cause a lot of frost to centralize in one location.

One great example where you can see that irrigation systems can actually protect your plants are vineyards. They will spray the grapes right before a frost so that the ice will protect them and keep them warm.

Frost protection in vineyard
Photo 34862376 © Nathanphoto | Dreamstime.com

To understand that, it’s necessary that we take a short excursion into physics. When a substance changes its state of aggregation, heat is released. Therefore when water freezes into ice, crystallization energy is released – and it’s probably more than you think. One liter of water that freezes generates as much heat as is needed to heat this quantity from zero to 80 degrees Celsius (176 °F).

If you actually use that technology, make sure that the water in your irrigation system won’t freeze! I’ve written an article about: How to Winterize an Irrigation System: A 3-step Plan, here you will find a lot of helpful tips and tricks.

How To Shelter Your Plants From Cold in the Winter

Another good idea for cold-weather plant care is to shelter your plants in the winter.

Here are some ways you can do this: 

  • Cover your plants: Covering your plants in the winter is a great way to protect them from harsh elements. You can use a wide variety of materials to cover your plants, which I’ll list later in this section.
  • Invest in a greenhouse system: Greenhouses can be an extremely effective way to grow your plants safely, no matter the weather. They are very good at trapping heat inside, protecting your plants from winter’s severe temperatures.
  • Utilize mulch: Covering the soil around your plants with a healthy layer of mulch can help protect your plants from frost. However, it’s important to only apply the mulch after the season’s first frost to correctly stabilize temperatures.

Here are some things you can use to cover your plants when it’s cold:

  • Thin fleece blankets or towels
  • Recycled newspaper
  • Old clothes or excess fabric
  • Burlap
  • Tarp
  • Bubble wrap
  • Thrifted bed sheets
  • Recycled cardboard

I’ve written multiple articles on frost cloth and how to protect your plants. Here you will find information about the frost cloth thickness, what plant covers you can use as well as frost cloth alternatives.

I highly recommend trying out these Trfoot Plant Covers (available on Amazon.com), which you can spread over your plants to keep them protected. I love these particular covers because they are much more affordable than expensive heating systems, easy to use, and high-quality.

You can also try using burlap. I recommend this Cleverbrand Burlap Plant Cover (available on Amazon.com) for its affordability and functionality. It’s also 100% natural and minimally invasive.

Investing in Plant Heaters for Winter

Another thing you can do to prevent excess frost damage to your plants is to invest in outdoor heating systems.

The downside to this method is that heating systems can get pretty costly, especially outdoor ones, as they usually require much more power and larger equipment than indoor heating.

However, heaters are usually pretty effective in protecting your plants from cold weather. Heaters can ensure that your water doesn’t freeze after you water your plants, so you don’t have to worry too much about waiting for the right temperature to water them or setting up winter-specific irrigation systems.

If the cost isn’t a problem for you and you’re interested in investing in plant heaters for winter, there are several types of heating systems you can choose from:

  • Electric heaters: Electric heaters provide a safe way to heat your gardens and greenhouses without affecting the moisture in the air as propane heaters do. Paraffin heating systems also impact moisture levels.
  • Fan heaters: Fan heaters help evenly distribute heat throughout an enclosed space. These are best for greenhouses.
  • Solar-powered heaters: Solar-powered heaters derive their power from the sun. The heaters then convert this energy into heat, making this method very safe, cost-effective, and sustainable since they don’t require electricity or gas.
  • Gas heaters: Gas heaters use gas sources to provide the equipment with power. Some heaters use propane gas, while others use natural gas. However, these can be expensive to maintain, as the gas will need to be replaced. They also require proper ventilation, which can be tricky to get right, and they are unsuitable for the environment.
  • Paraffin heaters: A paraffin heater is another heating method for your garden or greenhouse. However, like gas heaters, these are a fire risk and pricey to maintain. They are also unhealthy for the environment since they pollute the air quite a bit.

Watering Your Plants in the Morning To Avoid Excess Frost

Another way to protect your plants from winter frost is to water your plants in the morning. 

It’s important to remember that the time you water your plants is essential, and can often vary depending on current weather conditions. In the winter, it’s best to water your plants in the morning.

This is because it gets colder at night since there isn’t enough light and energy from the sun to warm things up.

Because temperatures significantly decrease when it’s night (in most North American climates), freezing is often more intense. Watering too late in the evening can cause dangerous amounts of frost to accumulate on your plants.

To solve this issue, try watering early in the day.

Should You Water Your Plants With Hot Water When It’s Cold?

Since some temperatures are too cold to water plants, you might wonder if there are any ways around this general rule. Is it reasonable to water your plants with hot water when it’s cold?

You shouldn’t water your plants with hot water when it’s cold, even in winter. This is because excessively hot water can burn parts of your plant, which is worse in the winter when they are most vulnerable. Lukewarm water is generally okay, but it shouldn’t be too hot, or too cold, either.

What Water Temperature Is Best for Watering Plants?

The best water temperature for watering plants is anywhere between 60-70°F (15.5-21°C), with the perfect middle spot being just about 65°F (18.3°C). While this does vary depending on environmental factors and species of plant, these water temperatures are generally the safest.

Check out my article about watering your lawn before a frost here.

Next, let’s talk about the ideal outdoor temperature for watering plants.

What Is the Ideal Outdoor Temperature for Watering Plants?

We’ve discussed what temperature is too cold to water plants, and what water temperature is best for this. But what about the ideal outdoor temperature for watering plants?

The ideal outdoor temperature for watering plants is 68°F (20°C). This temperature allows for maximum water absorption. While this can vary from region to region and species to species, this is generally the best watering temperature for most North American plants.

The reason why 68°F (20°C) is such an excellent temperature for watering your plants is because it helps incite certain mechanisms that allow the water to pump through the roots and distribute throughout the rest of the plant. It also maintains a good amount of oxygen at this temperature.

Again, it’s important to note that while 68°F (20°C) is generally considered to be the best outdoor temperature for watering plants, this isn’t necessarily true for every species of plant. This is because every plant has different climate and watering requirements.

The same goes for individual regions. No two environments are exactly the same, and there are important factors to consider depending on the region your plants are in, since climates, soil statistics, and other variables often change from location to location.

Final Thoughts

When winter arrives, gardening can become quite complicated as temperatures change. Sometimes, it’s too cold to water your plants.

It’s generally not a good idea to water your outdoor plants when the temperatures reach 40°F (4.4°C) or below. This is because 40°F (4.4°C) is very close to the freezing temperature of water, which can kill your plants because water expands when it freezes. This expansion causes plant cell walls to break.

Hopefully, this article provided you with enough information and tips to help your plants safely navigate colder temperatures.

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