{"id":4646,"date":"2023-03-30T20:20:30","date_gmt":"2023-03-30T20:20:30","guid":{"rendered":"https:\/\/weedmaps.com\/learn\/?p=4646"},"modified":"2026-02-22T13:09:02","modified_gmt":"2026-02-22T13:09:02","slug":"humidity-for-growing-weed","status":"publish","type":"post","link":"https:\/\/weedmaps.com\/learn\/the-plant\/humidity-for-growing-weed","title":{"rendered":"How to maintain the right humidity for growing weed"},"content":{"rendered":"
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Whether you're a home growing enthusiast or aspiring to the rank of Master Grower<\/a>, cultivating cannabis demands the ability to multitask, pivot on a dime, and pay keen attention to detail. Between deciding which cultivars to grow, what substrate to use, where to grow, which nutrients to use, and much more, humidity might not be something on a novice grower's mind. However, it's something experienced growers track quite closely.<\/p>\n\n\n\n

Along with light, temperature, and water, humidity is one of the most important environmental factors impacting your plant's health, development, and yield come harvest day.<\/p>\n\n\n\n

Below, find out the hows and whys of humidity and cannabis, guidelines for each phase of the life cycle, and answers to frequently asked questions surrounding humidity.<\/p>\n\n\n\n

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\n\tWhy is humidity important when growing cannabis?<\/h2>\n\n\n\n

Humidity is a measure of the amount of water vapor in the air. It can be measured in three ways: specific humidity, absolute humidity, and relative humidity. The one that is most easily measured and most commonly used in cultivation is relative humidity (RH).<\/p>\n\n\n\n

Relative humidity<\/a> is the ratio of water vapor present in the air versus the maximum amount of water vapor the air in a given area can hold at a given temperature.<\/p>\n\n\n\n

Temperature is an important part of the equation since humidity and temperature are closely related. The amount of water vapor that the air in a given area can hold will increase or decrease depending on temperature. The relationship between relative humidity and temperature is inverse: relative humidity drops when the temperature rises and increases when the temperature falls, assuming the water content in the air remains constant.<\/p>\n\n\n\n

Humidity is an environmental variable that impacts all plants, including cannabis. Importantly, it impacts two vital functions of the plant: transpiration and photosynthesis. Humidity directly affects pores on the leaf surface called stomata, causing them to open or close in response to humidity levels. These pores are important for both the release of water vapor \u2014 a process called transpiration \u2014 and for taking in carbon dioxide, which is needed for photosynthesis.<\/p>\n\n\n\n

When humidity is too high or too low, transpiration and photosynthesis, along with myriad downstream processes that are related to these two vital functions, are compromised, which will in turn compromise the growth and vitality of your plants.<\/p>\n\n\n\n

Not only is humidity important for plant health, but humidity levels are also important for controlling pests, diseases, and mold<\/a> since certain insects, fungi, and viruses and viroids thrive in moist conditions.<\/p>\n\n\n\n

Humidity can also impact the nutrient levels in your growing medium and how much water and nutrients your plant actually takes up from the medium, too.<\/p>\n\n\n\n

\n\tHumidity for each stage of the life cycle<\/h2>\n\n\n\n

The cannabis plant goes through different phases of growth and development<\/a> in its life cycle. As the plant evolves from a young seedling or clone to its vegetative and final flowering stages, so too evolve its needs for light, nutrients, and water, among other considerations.<\/p>\n\n\n\n

Since humidity plays an important part in plant health throughout the life cycle, a grower can adjust humidity at each stage to meet the plant's needs and optimize its growth. Generally speaking, humidity levels are highest when cannabis plants are young and will gradually decrease throughout the life cycle, reaching the lowest point during flowering.<\/p>\n\n\n\n

Note that these are general guidelines based on industry best practices and that many growers will evaluate optimal humidity levels for each individual cultivar they grow and the environment they are growing in by observing and tweaking over the course of several crops.<\/p>\n\n\n\n

Seedling and young clone phase<\/h3>\n\n\n\n

Seedlings and new clones do not have robust and established root systems from which to draw the water they need, so higher humidity levels help the plants take in water through their leaves.<\/p>\n\n\n\n

Ideal humidity range:<\/strong> High, 75 - 90%<\/p>\n\n\n\n

Vegetative phase<\/h3>\n\n\n\n

During the vegetative phase, the plant's root system is becoming fully established, and its energy is dedicated to growth and developing leaves. Humidity can be gradually decreased incrementally week by week to reach the level you will use while the plant is in flower.<\/p>\n\n\n\n

Ideal humidity range:<\/strong> Moderate to low, 70% at the beginning of veg, down to ~40% by flower<\/p>\n\n\n\n

Flowering phase<\/h3>\n\n\n\n

During this phase, the plant stops growing stems and leaves, instead focusing its energy on flower production. Lower humidity levels are ideal during this phase to minimize the chance of bud rot (botrytis)<\/a>. Growers often like to decrease humidity levels even further during the late stages of flowering.<\/p>\n\n\n\n

Ideal humidity range:<\/strong> Low, 40 - 50% during early flower, 30 - 40% during late flower<\/p>\n\n\n\n

Drying and curing phase<\/h3>\n\n\n\n

Even after harvest, humidity remains a concern when drying and curing<\/a> your flower. First, the harvested plants need to be dried. Then, the manicured buds are further dried in a process called curing<\/a>.<\/p>\n\n\n\n

<\/a>Ideal humidity range:<\/strong> Moderate, drying 50%, curing 55 - 62%<\/p>\n\n\n\n

\n\tHow to adjust humidity levels<\/h2>\n\n\n\n

If you're growing outside, there isn't much you can do to control humidity, but when growing indoors or in a greenhouse, there are several variables you can tweak to adjust the humidity in your growing environment.<\/p>\n\n\n\n

First, you will need a way of measuring humidity. In complex commercial growing operations, the facility will often be equipped with very advanced and sensitive climate control systems that will continuously monitor relative humidity and even make environmental adjustments as needed.<\/p>\n\n\n\n

For simpler grow rooms, a hygrometer is a must-have tool that measures relative humidity and air temperature. In fact, it's best to have at least three of these tools that can be placed at the high, mid, and low points of the grow room.<\/p>\n\n\n\n

Once you can measure the humidity in the grow room, think about the different factors that impact the humidity of the space, including:<\/p>\n\n\n\n