What is the Ideal Humidity for Seedlings?

Humidity is critical to every stage of plant growth. Different plants have different requirements at each of these stages. Usually, they need the most humidity during seed germination, up to 90% or nearly 100%. But once the seedlings have sprouted, they need lower humidity, at around 60% to 80%. 

Most mature plants need an average humidity of 50% to 60%. However, there are a huge variety of plants that thrive in different environments. For instance, tropical plants prefer high humidity levels up to 90%, while succulent plants can tolerate arid conditions with 10% humidity.

It’s important to maintain the right humidity for the specific plant at every stage. If moisture levels are too low, the plants may dry out and wither. On the other hand, too much humidity attracts pests and encourages the growth of mold and other fungi that may spread to the rest of your plants. Thus, you need just the right humidity levels depending on the specific plants.

Whether growing indoors or outdoors, you must also consider a lot of other environmental factors that are significant to plant growth, such as temperature, light, and airflow. All of these can also have some impact on the humidity levels. 

How Does Humidity Impact The Health of Your Plants?

First, you must understand what humidity is and how it relates to temperature. Humidity is the amount of water vapor in the air. When measuring humidity, we usually refer to the relative humidity (RH) or the actual volume of water compared to the maximum amount the air could hold at a given temperature, expressed as a percentage. In general, warm air can hold more water than cold air, but it doesn’t necessarily mean that hot climates are always humid.

For example, tropical plants need more watering in low humidity environments. You must adjust your watering schedule depending on the plant’s needs and the ambient humidity in your location. Humidity plays a significant role in photosynthesis as the plant absorbs moisture from the air around them. If moisture levels are too low, the plant loses more water than they can absorb. 

On the other hand, if moisture levels are too high, the plant cannot transpire or evaporate water into the air. It absorbs more water from the air and less from the soil. Too much humidity also creates a perfect environment for pests and fungal organisms that can kill the plant. 

Source of Humidity for Houseplants

Humidity will always be a part of the environment where there is heat and water sources. The humidity for outdoor plants largely depends on the climate. But indoors, humidity comes from any open water system. Plants naturally release moisture through the process of transpiration. The bigger the water source, the more likely you’ll have higher humidity.

In addition, when you water your plants, this water stays within the indoor environment. Plants absorb water and release the excess into the air. But if you overwater without proper drainage, this also produces extra moisture. Inadequate ventilation also limits air circulation, adding to the humidity in the space.

Ideal Humidity at Different Plant Growth Stages

Different plants have different humidity and temperature requirements at each stage of growth. Usually, they need the most humidity to germinate, then less and less as they mature. 

Germination Stage

Germination is the plant’s process of development from a seed. This is a crucial stage of plant growth as not all seeds will sprout into seedlings. Indoor germination is usually preferred as it gives you more options to regulate the temperature and humidity. Most seeds require temperatures between 68°F and 86°F (20°C to 30°C) and humidity levels around 90% or higher to germinate. 

If you are starting plants from seeds, you may soak them in water or place a wet paper towel around them to provide the humidity they need for faster and more successful germination. You may also keep your seed tray under a humidity dome. This is a cover made of clear plastic or glass to raise humidity levels for the seeds under the dome.

Once the seedlings have sprouted, they have to be transplanted in a larger space with proper temperature, humidity, and ventilation. At this point, you can reduce the humidity levels slowly. You also need consistent temperature when the seeds are germinating. Seedlings become more vulnerable to disease when temperatures fluctuate.

Vegetative Stage

During the vegetative phase, the plant starts to develop its leaves and extend its roots to absorb the required nutrients and water from the soil. At this stage, the plant needs less humidity, but in many cases, the more humidity the faster the growth. The plant also requires more light during this stage and humidity levels. Vegetation period humidity levels can range from 45% to 65% depending on the type of plant. The plant uses all the nutrients, water, light, and carbon dioxide it can absorb to create energy through photosynthesis.  

Flowering Stage

The flowering stage of a plant is when it devotes all of its energy into reproduction. The plant then produces flowers and eventually seeds, and fruits. At this stage, the plant needs even lower humidity. The flowering period humidity levels can be lowered to 40% or 50%. Some may develop faster in higher humidity up to 70%, but it all depends on the plant and its native environment.

Flowering Stage

Signs that Your Cannabis Plant Needs More Humidity

All plants need water to grow and develop, especially in the early stages. Depending on the moisture content in the air, you may need to water your plants less. If you live in a low-humidity area, watch out for the following signs that will tell you when your plant needs more moisture.

Check the top layer of the soil. Seedlings need a lot of water. Since they are still developing and need all the nutrients they can get from the soil, they aren’t able to store water for a long time. They need the soil to be constantly moist but not too wet or the developing roots may drown. Just touch the top of the soil to check if it needs more water.

If you have extremely dry air, the water may evaporate faster than the plants can absorb it. In this case, you may see visible signs of dryness in cannabis plants. You may notice the tips of the leaves turning brown due to lack of humidity or too much light.

In later stages, lack of humidity can also dry out the leaves even if you water your plants regularly. The leaves may become brittle and wrinkly. Inadequate or inconsistent watering may stress the plants, causing the leaves to droop and wither. Lastly, lack of water starves your plants, causing them to grow more slowly or stop growing altogether.

How to Increase the Humidity for Plants

If low humidity is a constant problem for your plants, the good news is, it’s pretty easy to increase humidity levels. If starting plants from seeds, the best way to provide high amounts of moisture to improve germination is by using a humidity dome. You may use store-bought humidity domes or make one for yourself.

Once seeds have sprouted, you can remove the seedlings from the dome and transplant them. Group your plants together just close enough that they are not touching. Through transpiration, plants release moisture into the air, raising the humidity levels within that area. 

One instant way to add humidity to your plants is by misting them. Some houseplants like succulents rarely need misting. This is particularly helpful for tropical plants that prefer more humidity. Too much moisture for plants that prefer arid conditions can cause mold. But if low humidity is a particular problem in your place, you may need to mist most plants every two to three days along with weekly watering.

In case of extremely low humidity levels, you may also use a humidifier to add moisture to the air. A portable humidifier is the most common solution to low humidity levels, particularly during winter. Instead of supplementing only your plant’s humidity needs, a humidifier can help raise humidity levels for the whole room or even your entire home. With larger models, you can even set the exact humidity level you need. Only, one drawback is that you need to refill the humidifier tank with water at least once a day.

If you plan to expand your plant collection, you may want to invest in an indoor greenhouse. It is the best solution to control the environment for all types of plants, from the temperature, humidity levels, and light. It is especially useful for growing plants out of season for year-round harvest. Greenhouses are designed so to trap the heat and humidity inside the area, providing your plants’ needs even with less than ideal conditions outdoors. 

You can keep the humidity levels inside a greenhouse around 50% to 60% or higher depending on your plants’ requirements. You can either buy a prefab greenhouse or build one in your backyard. Take note of any requirements in case you need a permit to build a greenhouse where you live.

Signs of High Humidity

While humidity is generally good for most plants, too much of it can also cause problems. Outdoor growing has greater advantage in this regard as the climate determines the temperature and relative humidity for your plants. But for indoor growing, you usually have limited airflow, producing more moisture that can also become harmful to your plants.

The optimal range of relative humidity for indoor plants range from 40% to 60%. Depending on the type of plants and the current stage of growth, too much humidity can be dangerous to them. Condensation on windows, metallic surfaces, or any colder surface inside the grow room, tent, or greenhouse is a common first sign of excess humidity.

Newly sprouted seedlings need constant moisture, but too much of it can also kill your plants before they even take root, or what is commonly called the damping-off disease. When infected, the leaves of your new seedlings turn brown or gray and the stems become soft and thin.

For grown plants, too much water is also harmful. The soil needs to dry out a little in between waterings. Too much moisture allows mold and other fungi to grow. White, fuzzy mold or powdery mildew on the leaves or stem are common to plants in high humidity. Once a plant becomes infected, there are high chances that it spreads to the rest. 

Signs of High Humidity

Another sure sign of high humidity problems is when you find puddles of water around your plants a long time after watering. This means you’re overwatering them and the water is not draining properly. Too much water makes the soil more hospitable to unwanted organisms. If you see pests such as aphids, ants, caterpillars, or spider mites, this could mean that there is too much humidity. 

How to Lower the Humidity

If you’re housing yur plants in a grow room or grow tent, ensure that it is properly insulated to maintain the temperatures inside even with sudden temperature changes outside. It also maximizes the efficiency of any electrical device inside like an air conditioner, dehumidifier, fans, and lights.

In extreme humidity, you must also consider the type of soil you use for your plants. Depending on the specific plant’s needs, you should choose the right type of soil with excellent drainage capacity. Well-draining soil ensures that there is not excess water that can cause soggy soil, root rot, and potential mold growth.

Remember that plants naturally release moisture into its environment. The amount of water you give them is also the amount that evaporates into the air. So to prevent excess water, you want to avoid overwatering your plants. Don’t let standing water stay in the area for long. 

If high humidity is a common problem for you, place your plants near a window to add some airflow. This also provides some natural light that your plants need. If possible, open the windows early in the morning or late at night to let some cool air in. However, this is only ideal if there is less humidity outside. 

If you can’t open the windows, turn on your fans to circulate the air and help dry out the excess water by evaporation. Commercial greenhouses have ventilators for this purpose. In alternative an air conditioning unit can also help regulate indoor humidity to a certain degree. 

Most plants can also greatly benefit from grow lights. If you’re growing different types of plants in a grow room, adding grow lights to your system can help all your plants when there is a limited source of natural light. Although, note that grow lights also produce heat, which may speed up evaporation and raise humidity levels. To prevent this, you must also add ventilation or use the lights only during the coolest time of the day.

Give your plants space to promote airflow. While it’s recommended to group similar plants together, just like you, they need their own space to breathe. Larger plant leaves shade the smaller ones from the light. Also, placing plants too close together produces excess moisture. This can cause fungal growth and diseases which can spread quickly if plants are too close to each other. 

Excess humidity can bring a variety of problems to your plants at its later stages. For indoor growing areas, you can use a dehumidifier to reduce humidity effectively. There are many different types and sizes of dehumidifiers. The unit you need depends on actual humidity, the size of the area, and the requirements of your plants. 


Growing from seedlings indoors allows you to cultivate plants at any season with the environment mostly in your control. This also gives you greater responsibility to maintain the correct temperature and humidity levels at each stage of the plant’s growth. Remember that different plants thrive in different environments. When starting plants from seeds, you need 90% to 100% humidity. A humidity dome improves seed germination by providing the needed moisture for your seeds to sprout faster.

Once your seedlings have sprouted, you can slowly reduce the humidity down to 50% to 70%. You must know the exact requirements of the plants you’re growing and monitor them to see how much and how often you need to water them, whether they need full sun or they can grow under shade.

Mature plants typically need humidity levels around 40% to 50%, but it can vary depending on the type. Tropical plants may need up to 75% humidity to develop fruits, while succulent plants can tolerate low humidity down to 10%. Watch out for the signs of either low humidity or high humidity so you can find the right solution as soon as you can.

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