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It’s the middle of winter, and with daytime temperatures getting into the teens or single digits, the heat is running constantly. This makes the air in my house dry, and some of my plants seem to be suffering from the low humidity. I decided to do some research to find out what humidity level is best for plants. So, what is the best humidity level for plants? An ideal humidity range for most mature plants is 50% to 60%. Some tropical plants, such as pineapple, are accustomed to humidity levels up to 90%. Many succulents, such as cacti, will be fine with humidity levels as low as 10%. As a general rule, plants with thicker leaves can tolerate lower humidity levels. Of course, your target humidity level will depend on the type of plants you are trying to grow. The ideal humidity level also depends on the stage of a plant’s development. In addition, temperature has an effect on humidity, and sometimes you will optimize one at the expense of the other. In this article we'll talk about: what humidity ishow to measure humidityhow a plant's humidity needs change with its stage of growthsymptoms of plants when humidity is too low or too highhow to adjust humidity levels Let's get going. What is Humidity? Humidity tells you how much water vapor is in the air. When temperatures rise, water evaporates faster, turning into water vapor and increasing humidity. Higher humidity increases the chances of rain, fog, or dew (the water droplets you sometimes see on grass first thing in the morning). How Do You Measure Humidity? A hygrometer is one tool that can measure humidity. If you have a dehumidifier in your home, you can use it to provide an estimate of the humidity level. A dehumidifier will remove some moisture from the air. First, raise the humidity setting until the dehumidifier stops running. Let’s say this happens at a setting of 50%. Then, you know that the humidity level is 50% or below. Then, decrease the humidity setting until the dehumidifier starts running again. If you decrease the setting to 45% and it starts running, then you know the range is 45% to 50% in your house. Of course, remember that the humidity can vary by room, due to air currents. Basements tend to be cool and damp, with higher humidity levels than the rest of the house. The Best Humidity Level For Plants (Based On Stage of Plant Growth) According to the University of Vermont Extension, many houseplants prefer a humidity level of 70% to 80%. This humidity level is much higher than you can ordinarily provide indoors. As a result, the University of Nebraska-Lincoln Extension suggess that the humidity level should be between 40% and 60% for houseplants. In fact, a humidity level lower than 20% will injure most houseplants (the exceptions would be cacti and succulents, which tolerate dry conditions). The table below gives you some guidance on air humidity levels and a description that includes what plants might prefer them. Humidity LevelDescription0%No moisture in the air.Difficult even for cactito survive.10% to 20%Cacti and succulentscan survive. Air thisdry will injure mosthouseplants.20% to 30%This is the humiditylevel of an averagehome. Some plantswill be able to live,including cacti andsucculents.40% to 50%This is ideal for theflowering stage ofmature plants.50% to 60%This is ideal for thevegetative stage of growing plants.60% to 80%This is ideal for agreenhouse, whichcan be used to growvarious plants, bothtropical and otherwise.90% to 100%This is ideal for thegermination of seedsand growth of someseedlings. People wouldfind it uncomfortable.A table of humidity levels and a description of each. As your plant goes through its growth cycle, its humidity needs will change. Early Stages For seeds to germinate, the humidity level should be high, in the 90% to 100% range. If you are starting plants from seeds, keep them under a humidity dome to keep the humidity high. A humidity dome is a clear cover made of plastic or glass that allows light through and keeps moisture under the dome, to raise the humidity level for plants inside the dome. A humidity dome will also have openings that you can seal off to increase the humidity, or open to decrease humidity. For more information, check out my article on humidity domes. Seedlings are seeds that have sprouted and grown leaves, but are still small. Once your seedlings emerge from the soil and are strong enough, remove the humidity dome. Otherwise, you run the risk that your plants will succumb to the growth of fungus or disease. You can grow lots of seedlings at once with seed trays, as long as the humidity is high enough. If you are interested in growing seedlings on a large scale, check out this article on greenhouses from the University of Massachusetts at Amherst. Vegetative Stage The vegetative stage of a plant is an intermediate stage of growth between germination and flowering. During this phase, the plant extends its root system to absorb more nutrients and water from the soil. A purple velvet plant in the vegetative phase. The plant uses the nutrients and water, along with light and carbon dioxide, to create energy through photosynthesis. The plant uses this energy to grow taller and stronger, and creates leaves to absorb more light. A plant will want far lower humidity during the vegetative stage than during germination. An ideal humidity range for the vegetative stage is 50% to 60%. Flowering Stage The flowering stage of a plant is the stage where flowers are produced, followed by fruit. In this stage, the plant devotes the energy it has produced (and is still producing) to flowers and eventually seeds, nuts, fruit, or vegetables. A peach tree in the flowering stage. A plant will want even lower humidity during the flowering stage than during the vegetative stage. An ideal humidity range for the flowering stage is 40% to 50%. Symptoms of Plants When Humidity is Too Low In a process known as transpiration, water moves from the plant’s roots to the leaves, where it evaporates into the air. When humidity levels are low, the plant loses more water due to transpiration. Combined with dry soil, this can lead to a lack of water for the plant. Some symptoms of plants when the humidity is too low include: leaves dry up and curl, or turn brownA wilting or drooping look (a “lazy” plant that looks like it wants to lie down and rest)The flowers fall off, or they do not form at all Often, low humidity will occur in your home or office, due to HVAC (heating, ventilation, and air conditioning) systems, which remove humidity from the air. In fact, humidity levels can get as low as 10%! This is especially common in the winter months, when cold temperatures cause heating systems to run almost constantly. How Do You Add Humidity to Plants? (Raising Air Humidity Level) There are several ways to raise the humidity level of the air in your home, including: use a humidifieruse a spray bottle (plant mister)boil water or run a hot showerkeep plants close togetherhang clothes to dryuse a humidity dome or greenhouse You can combine some or all of these methods to amplify the effect, which may be necessary for plants of a tropical origin. Use a Humidifier One way to increase the humidity level in the air is to use a humidifier. A humidifier is a machine that adds water vapor to the air by the process of evaporation. One advantage of a humidifier is that you can select the humidity level and set the device to work. It will continue working until the humidity in the air reaches the desired level. One drawback of using a humidifier is that you will need to replenish the water every so often (more often in a dry home with a forced hot air heating system). Exercise caution when using a humidifier, since too much humidity can promote the growth of mold in your home. According to Wikipedia, a humidity level of 30% to 50% is appropriate for most homes. If you still decide to use a humidifier, consider restricting its use to one room that is sealed off from the rest of the house. That way, the machine won't be running constantly and wasting electricity in trying to add moisture to the air. After all, you can always put your houseplants in that one room and spend some time there enjoying them. Use a Spray Bottle (Plant Mister) If you have an empty spray bottle in your house, you can clean it out and use it to increase the humidity level for your plants. Just fill it with water after cleaning, and then spray some water onto the leaves of your plants. Plants that prefer more humidity (such as tropical plants) will do better with this method than plants that like dry conditions (like cacti). Just be careful not to overdo it with a spray bottle. Adding too much mist for plants that prefer dry leaves can cause fungus (mold) and other problems. For example, the University of Maryland Extension recommends not using a spray bottle on plants with hairy leaves, such as African Violet. A spray bottle can be used for increasing humidity, but also for cleaning dust off of your plant's leaves and much more. You can learn more about plant misters and what you can use them for in my article here. Boil Water or Run a Hot Shower Another way to increase the humidity in your home is to boil water or run a hot shower. Normally, the steam from a hot shower or boiling water on a stove is vented out of the house. However, if you leave the vent fan off, the humidity will stay in the air. This will provide some extra humidity for houseplants that you might have in the bathroom or kitchen. This method uses a lot of energy to heat up the water, but there is no harm in doing it if you were already planning to take a shower or boil water. Sometimes, your houseplants start to wilt and look a little sad due, to low humidity. This goes double in in the winter, when the heat is running and drying out the air. One solution is to put the plant in the bathroom for a few days. This will provide a high humidity environment while it recovers from the dry air. Keep Plants Close Together To raise the humidity level in an area, try placing multiple plants close together. This will raise the relative humidity in the local area. Just be careful about putting too many plants too close together, since the reduced air circulation and proximity of plants can give rises to diseases, fungus, and other problems. Hang Clothes to Dry You can also simply hang clothes to dry in your house after you have washed them. Not only will this reduce your electricity bill, but it will also increase the humidity level in the air when the water evaporates from the clothes. One drawback of this method is that it takes up more space than any of the other methods. However, if your plants like higher humidity, then hanging clothes on a rack in the same room as the plants may help them to grow better. Use a Humidity Dome or Greenhouse As mentioned earlier, a humidity dome is useful for the early stages of plant growth (especially germination). This is because the soil needs to stay moist to encourage proper germination, and to give seedlings the water they need to grow. A greenhouse is another option to maintain higher humidity levels for your plants. If you are growing tropical plants or germinating seeds, low humidity could kill your plants or cause a poor seed germination rate. To increase the humidity level, make sure the greenhouse is totally sealed. Leave the door closed, and make sure any vents or windows are closed as well. Also, leave an open container of water inside the greenhouse. When the greenhouse warms up from sunlight, the water will evaporate into the air and increase the humidity level. Is High Humidity Good For Plants? (Symptoms of Plants When Humidity is Too High) As mentioned earlier, high humidity is good for some plants, but not for others. When humidity levels are too high, the plant cannot evaporate water from its leaves by transpiration. This prevents the plant from cooling. When temperatures are high, this can lead to the plant overheating. If the soil is wet, it will stay wet longer, and the plant may suffer from root damage due to rot. You may also see signs of decay on your plants. Plants may display some of the following symptoms when the humidity level is too high for them: Mold on leaves or flowersRotten leavesRoot damage Another problem caused by high humidity is mold growth, which is especially common in basements. Air does not circulate as freely in the basement, and humidity may already be elevated due to proximity to the damp earth. Your greenhouse can also become too humid if it is sealed tightly and the outside humidity is also high. Ways to Lower Humidity (How to Lower Humidity In Your House) Luckily, there are several ways to lower the humidity level so that your plants can thrive: use a dehumidifieruse a fanuse air conditioning Use a Dehumidifier One way to reduce humidity is to use a dehumidifier to remove water vapor from the air. The dehumidifier will turn the water vapor from the air into liquid water, and you will need to empty the water tray regularly. With some dehumidifiers, you can connect one end of a hose to your dehumidifier and put the other end directly into a sink to drain the water out continuously. This will allow you to avoid emptying the dehumidifier by hand. Use a Fan You can also use a fan to lower the humidity of the air in your house. A fan will bring dry air from other rooms into a humid room that contains plants. You can also try spacing your plants further apart. This will allow for more air circulation from the fan, which will dry out the air faster. Use Air Conditioning An air conditioner is often thought of as providing cool air. However, in addition to cooling air, it will also remove moisture from the air. Remember that warmer temperatures mean that the air can hold more water vapor. Likewise, cooler temperatures mean that the air can hold less water vapor. For example, air at 60 degrees Fahrenheit will hold twice as much water vapor as air at 40 degrees Fahrenheit. Every time the air temperature increases by 20 degrees Fahrenheit, the air will be able to hold twice as much water vapor. Don’t run to change your thermostat just yet, though. As mentioned before, there are ideal levels for both temperature and humidity. Plants need both proper moisture levels and the correct temperature. It is a balancing act, and optimizing one comes at the expense of another. If you want more information on humidity levels for a greenhouse, check out this resource on lowering humidity from the University of Massachusetts at Amherst. Conclusion Hopefully, you have a better idea of how humid your house should be in order for your plants to thrive. You also have some ways to increase or lower the humidity, if necessary. I hope you found this information helpful. If you have any questions, please leave them in the comments.

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