- Enrich the soil with tomato fertilizer to help your plant grow as healthy as possible. Although tomatoes aren't as fussy with the soil, mixing the soil with some organic compost or nutrients will aid in the plant's growth. Indoor gardens don't have the type of nutritional soil found in nature. Adding your own peat moss or worm castings will be helpful.
- Regulate the sunlight carefully because tomato plants need a good amount of sun for optimal growth. Place your indoor tomato plant in front of a sunny window for no less than eight hours a day. Ideally, it should be out in the light for most of the day. Keep your plant warm, up to about 75 degrees Fahrenheit. Consider putting a fishbowl over it for a greenhouse effect if your house is cool. Supply the soil with peat moss, which will keep in warmth.
- Water slow and deep, aiming right at the tomato plant's roots. Watering too high, like at the leaves, can allow for water evaporation. Don't rush when you're watering an indoor tomato plant. Use a watering device with a spout so you can aim the water at all areas of the soil. Do this once every two to three days. Applying mulch in the soil will help contain moisture. Improper watering will lead to stunted growth and reduced fruit production.