In about 30 days it will be time to plant these tomato plants in the garden. Until then they have some more growing to do. Also, the plants must be “hardened off” which is a process of acclimatizing tender indoor plants to the outdoors. Leaves will become tougher, pigments darker, and stems thicker. In the house under fluorescent lights growing conditions are mild. The air is uniformly warm, humidity is constant, there is no wind, and, most importantly, the light intensity is weak compared to natural sunlight. If indoor plants are put into direct sunlight they will scorch in just a few hours. Weeks of work growing them for transplanting will be lost. The plants might not recover.
To harden off plants I give them a few hours a day of indirect light under a tree. After about three days they get some exposure to full sun but only for an hour or two. By the end of the week they are ready for full sun exposure. It is important to keep the plants watered as just a few hours of warmth and wind can dry out their pots.
The plants must also become adapted to cooler night temperatures. I follow a similar process of gradual exposure. A few hours in early evening then they’re brought indoors. I do this for about a week. When I think they are strong enough to stay out all night I keep them close to the house and will cover them with a light sheet at night if temperatures will be lower than 40 degrees.
The big day is in June and that’s when the tomato plants will be planted into the garden.