Hello. I started my tomato plants inside my house about 4 weeks ago. I moved them from under my lamp to beside my patio window to acclimatize them. The leaves started to curl and turn brown. How do I correct/save my tomatoes?
Hello, Thank you for contacting Toronto Master Gardeners.
Young tomato plants are sensitive to change. Several factors could be working to cause the leaf problems you are seeing.
If the area you have them in now is in full sun the temperature is probably much higher than the temperature under your grow lights. With the hot sun hitting the plants, leaves will increase their photosynthesis as well as transpire water to the air in an attempt to cool down. The water requirements could be very different in this new environment. This could easily dry out the leaves and cause some curling and scorching. I would return them to their original location and make sure they are well watered but not sitting in water.
If your plants are in small pots they may also need to be transplanted into larger containers. Re-potting gives them new soil and nutrients as well as encourages root growth which leads to a healthier plant. If you transplant the seedling deeper in the soil than the previous container, the tomato will grow roots along the buried stem giving the plant a stronger root system and more stability.
When they have regained their strength, try placing the tomato plants outside out of the direct sunlight. Outside they will have good air flow and not heat up as much as they did with the sun was shining directly on them through glass. Bring the plants inside over night. Slowly increase the amount of sunlight they are exposed to during the day. Make sure they have enough water and they should respond well. Keep a close eye on the weather so they are not left out when the temperatures are chillier. It will still be a few weeks before you can dependably leave them outside over night.
I have included some links below that discuss tomatoes and hardening off of seedlings.
Good luck and I hope you have a bumper crop.