Humidity inside a plant is close to 100%. Along with that, humidity in the native habitat of tropical and subtropical plants runs at about 80%. Inside our homes things are quite different. Most houses average between 35 and 65 percent humidity and some fall below 20 percent during the winter season when the heating system runs; air conditioners also dry out the air considerably.

        
* click on an image for a larger format *

A plant growing in a room where humidity levels are too low will lose moisture rapidly; humidity partly controls the moisture loss from the plant. On a plant’s leaves there are tiny pores called stomata. Through the stomata carbon dioxide enters and water and oxygen leaves. The lower the humidity, the faster the moisture loss.

Most houseplants adapt to the lower levels of our homes - even though they prefer higher humidity – but will do best when humidity levels are close to 50 percent (many of them will be reasonably tolerant if levels are at least between 40 to 50 percent). Even cacti, succulents and plants native to dry desert environments that tolerate lower humidity levels prefer the levels of humidity not to drop below 20 percent. The Sahara Desert has an average humidity level of 25% whereas our homes can plummet down to less than 20% during the winter with the heating system on.


What Do The Plants Say About This?

If a plant is living in extremely low levels of humidity it will display a variety of symptoms caused by its stressful environment, the most common one being brown leaf tips and edges. The edges and tips may literally look burned.

As a rule, if a plant that prefers a more humid environment is forced to grow in your ‘Sahara-desert-style’ environment its younger leaves and the leaf tips of established growth will suffer. The most actively growing cells – and the ones most susceptible to dry air - are in the new leaves and leaf tips of your plants. Plants dealing with humidity levels that are too low will frequently shed flower buds, and flowers that have managed to open may die prematurely. Even older leaves on certain plants may be shed as a result of rock-bottom humidity.

        
* click on an image for a larger format *

As if your houseplant wasn’t suffering enough with the rapid moisture loss, humidity levels that are detrimentally low are a warm invitation to insects, one of those being the ever popular red spider mite that will move in happily and thrive joyfully in the warm and dry atmosphere your plant is suffering in. And since your plant is stressed, who has the upper hand? The cozy mite or the frazzled plant?

So what do the plants say about low humidity? They don’t like it – not one bit.

Increasing & Controlling Humidity

There is no need for your houseplants to suffer inappropriate humidity levels. There are many ways that you can increase the humidity in your home, in individual rooms or around your plants.

Misting

Misting plants adds a layer of water on the leaves and reduces transpiration. However, this form of relief from low humidity only lasts for a few minutes. Very soon after misting, that water will evaporate and the air surrounding the plant is once again low in humidity. You would have to mist every few minutes, all day long for this method to be significantly effective. Another thing to bear in mind is that plants that are misted too often have the potential of developing fungal growth and tissue rotting. It is not a bad idea to mist, just be prudent and mist early enough in the day to give your plants enough time to dry to avoid fungal development that is most likely to develop if plants are wet at night.

One of the most popular methods used to raise humidity around a houseplant is a pebble tray. Fill a large plant saucer with pebbles, stones, rocks, polished glass or similar material and fill it with water. Place your potted plant – or a number of plants depending on the size of the pebble tray – on top. The water will evaporate and increase the humidity around the plant. It is better to choose a saucer/tray that is large enough to be effective; the larger (wider) the pebble tray, the more effective it will be.

* Note: Make sure that the bottom of your houseplant’s pot – if the drainage holes are exposed - is not sitting in water because this will lead to root rot. To avoid this, either keep the water level lower - so that it does not come into contact with the pot - or keep a saucer under your plant’s pot that will sit on the pebble tray instead. *

(The above note of caution does not apply to hydroculture plants, only to soil-grown ones. In hydroculture, the plants have water roots and won't be faced with that problem)

This is another popular and effective method that can be used to increase humidity. Take a potted plant – or a number of small potted plants – and place it in a larger pot. Fill (line) the empty spaces between and around the small pot with peat moss and keep the moss constantly moist. Water that evaporates from the peat moss will help to increase the humidity around the plant.

Different rooms in our home have different levels of humidity. Bathrooms and kitchens, for obvious reasons, often have higher humidity levels than other areas in the home. If some of the other requirements are suitable – temperature & light – place the houseplants that require more humidity in your bathroom or kitchen.

Grouping plants close together helps to increase the moisture surrounding them. This forms a microclimate with higher humidity. Moisture loss from one plant can benefit the plant next to or near it. This is a simple and effective alliance for humidity lovers.

Undeniably, the most effective way to increase humidity is by using a humidifier. Not only will you be able to control the humidity levels in your home but both you and your plants will benefit with proper levels of humidity, for your health and theirs.

Too much humidity is just as damaging as too little. Signs of too much humidity are patches of gray mold, rot on leaves or stems and flowers covered with mold. You should decrease humidity if this occurs and increase the air movement in your room and around your plants. Too much humidity is not only detrimental to plants but it also has very negative effects on your health and can cause considerable damage to your home and furniture.

There are a variety of humidity indicators (hygrometers) available for purchase, many of them very inexpensive. These indicators will give you an exact humidity reading that will help you to determine how to handle the levels in your home – increasing or decreasing them as necessary.

There are certain plants that you will not be able to accommodate with conventional methods no matter how much you try because you can’t raise humidity levels to a point that is harmful to your health and the stability of your home. For those plants that require extremely high humidity, it is best to grow them in terrariums or closed containers where you will be able to regulate their humidity.