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Growing Indoor Tomatoes FAQs: Frequently Asked Questions

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Updated 9.28.24

Tomato Dirt answers readers who need information for growing indoor tomatoes FAQs.

FAQs about growing tomatoes indoors with Tomato Dirt #HomeGardening #BeginnerGardening #VegetableGardening

Q. What are light source options when I grow tomatoes indoors?

A. Grow tomatoes on a windowsill, under grow lights, or in a green house.

Q. How warm must I keep my indoor growing area?

A. Tomatoes grow best when the indoor temperature is 75-85ºF, but you can get by with setting your thermostat at 65ºF. (Don’t go lower than that, however.) You can help keep your plants warm by placing them on a seedling heat mat or running a space heater in the growing area.

Q. How long should I run my tomato grow lights each day?

A. 12-16 hours.

Q. If I keep plants under lights for 24 hours a day, will they grow faster?

A. No. Tomato plants need at least 6-8 hours of darkness each day. Turn off the lights at least part of the time.

Q. How do I know when to replace my growing light lamps?

A. Each lamp type has a designated life span, expressed in number of hours used. While the lamp may not fail as it ages, it loses output capability. Replace lamps as they approach the designated number of hours used.

Q. How much is the electrical cost to running a tomato grow light system?

A. Here’s how to calculate cost per hour:

To determine total wattage used: add the total amount of your system’s wattage
To determine kilowatts used: divide total wattage by 1,000
To determine cost per hour: multiply number of kilowatts used by your electric company’s kilowatt hour rate.
To calculate cost per month: Multiply cost per hour by the number of hours used per month

Q. When can I grow tomatoes indoors?

A. Anytime.