Humidity for House Plants

Most plants need humid air in order to thrive. That’s because the pores through which they breathe lose most of their moisture when the surrounding air is dry, a loss that the plant can’t always replace through the water its roots absorb. The thinner the leaf, the greater its need for humidity. Thick, leathery, or waxy leaves, or those covered with hair, are usually relatively immune to dry air.

Symptoms of dry air include curled leaves and dry leaf tips, as well as a frequent need for watering. Flower buds are especially susceptible to dry air and may turn brown or simply fall off if humidity is too low.

spraying house plants
Spraying house plants with water is a good way to increase humidity.

The humidity level in the average home is often below 30 percent, yet most house plants, even desert dwellers such as cacti, prefer humidity levels of at least 40 percent. Many require 60 percent or more. Relative humidity of 50 to 60 percent is probably ideal for both house plants and people.

Regional and Seasonal Variations

In some areas of the country, dry air is a chronic problem, especially in the arid Southwest. During periods of extreme heat, air conditioning has a further drying effect on the air. In such areas, the year-round use of a humidifier may be necessary.

In areas with cold winters, humidity levels drop indoors during the heating season. That’s because the relative humidity of cold outdoor air drops as it is warmed up. Certain heating systems, such as electric heat, compound the situation by further removing humidity from the air. In such cases, some sort of system to compensate for low humidity may be necessary during the winter months.

Air Circulation

Plants outdoors are exposed to air currents of all sorts, and many seem to need a certain amount of air movement indoors. Air circulation helps ventilate waste gases, remove excess heat, and prevent diseases that can develop in closed spaces. There is often adequate air circulation near large windows because of temperature differences between day and night, but elsewhere, especially under plant lights, it is wise to run a small fan to keep the air in constant movement. Don’t direct the fan on the plants. Just having it in the same room will provide the circulation needed.

Easy Ways to Increase Humidity

The best-known method of increasing air humidity is spraying houseplants with warm water. Unfortunately, this is not terribly efficient, since the humidity provided dissipates rapidly. To efficiently raise humidity by spraying, repeat the process several times a day.

A room humidifier will do wonders in increasing air humidity. Just make sure to fill it up regularly. Some modern homes have built-in humidifiers that can be adjusted to the desired level.

It is easy to build a plant humidifier of your own. Simply fill a waterproof tray with stones, gravel, or perlite and pour water over them so that the bottom ones rest in water while the upper ones are dry. Set the plants on one of these pebble trays. They will benefit from the added humidity given off as the water evaporates. By keeping the tray constantly half-filled with water, a nicely humid microclimate will be created.

For house plants with moderate humidity needs, grouping them together during the heating season is a simple solution. Each plant gives off humidity through transpiration. Clusters of plants will create very good humidity in the surrounding air.

Terrariums

Delicate, thin-leaved house plants require a humidity level of over 70 percent, a level that is hard to achieve in a large room. If this level is impossible to maintain, a terrarium, easily made from an old aquarium, can be the best solution. Fitted with a glass lid, it creates a microclimate in which humidity levels rise to almost 100 percent. Just open it slightly for ventilation if water droplets form.

In the next section, we'll talk about temperature for house plants.

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