Ideal Humidity for Indoor Tomato Plants

Ideal Humidity

• You need a well-lighted sun room to successfully grow tomatoes indoors. Tomatoes need a minimum of six hours per day of direct sunlight, warm soil and 60 percent humidity to grow well indoors. With proper watering, tomatoes can tolerate humidity from 40 to 80 percent. Tomatoes can actually grow more quickly indoors, but only if you provide proper conditions. Air-conditioned or heated air can be as dry as desert air.

High Humidity

• High humidity condenses on plant leaves, providing a harbor for fungus spores that float around in the air in most homes. Don't handle wet leaves or stems to avoid spreading fungus spores to other parts of the plants. Smoking and tobacco products can pass deadly tobacco mosaic viruses to your vines. Sunshine helps reduce leaf diseases, but also reduces humidity around the plant. A sudden temperature drop in humid air can produce condensation on leaves and smooth surfaces. Fungus spores and mildews collect in wet spots. Wiping everything dry and using a bleach solution on metal, plastic and glass surfaces helps remove spores that can infect your plants.

Low Humidity

• A real problem in wintertime when the heat's on is very low humidity. Dry air sucks the moisture out of the soil around the plant. Check the soil every two days and water well enough to keep the soil moist, but not wet. In very dry conditions, mist the leaves lightly every day. A ceiling fan or oscillating fan near the plants moves air to keep the plant dry so that it doesn't attract fungus spores.

Pollination

• Tomatoes are technically self-pollinators, but are singularly poorly designed for the job. Bees and butterflies help with the job, but since most people don't like turning bees loose in the house, it remains for the grower to do the job. As soon as flowers appear and begin to open, shake or dust the tomatoes with a feather duster to stir up pollen. Having a fan blowing gently among the plants helps spread pollen. Humidity during pollination needs to be 65 to 70 percent to ensure that the anther is "sticky" enough with moisture to capture pollen. The best time for pollination is at midday when conditions are best. Pollinating in early morning or late at night produces less fruit.

Irrigation

• Root systems for tomato plants must be well-drained. Root rot is a real problem with container-grown tomatoes. An exhaust fan that can change out the air in the growing room in just a few minutes controls not only moisture, but also mold, fungus and mildew spores. Run the fan every day or two to keep spores released by the soil or by infested plants from producing colonies inside your grow room. A steady breeze around plants also reduces the numbers of insect pests that can establish on leaves, stems and fruits. Placing decorative stones in trays underneath the tomato plant containers helps retain water left over from watering your plants and increases humidity in the room.