Whether interested in growing a hybrid Better Boy tomato or a Cherokee Purple Heirloom, we all have read on the back of tomato seed packets the number of “days to the maturity,” but what about days to transplanting outdoors?
One may ask “When should we start our tomato seedlings indoors and what is the right size for transplanting into the garden?”
Knowing the right amount of time to grow tomatoes indoors before transplanting outside can increase efficiency of production space and the probability of successful transplanting.
When I was an employee of a local greenhouse in St. Louis, the third week of March our germination chamber shelves were packed with flats … and more flats of newly planted tomato seeds. The third to last week in March is the perfect time to start tomatoes and peppers indoors from seed. This allows them about a month of growth indoors before being transplanted outside into your garden.
“Why is it so important not to start your tomatoes too early indoors?” an eager gardener may ask.
The answer from experts is that tomatoes and peppers are less stressed when initially transplanted outdoors if they are not “too mature.”
Tomatoes ready for transplanting should be well rooted yet not “root bound” stretched, or overgrown for their pot, often a 1204 tray insert called a “four pack” or a 4-inch pot.
The first rule in starting seeds indoors is to be proactive against pathogens and start with a sterile growing medium as well as pots and trays. I prefer to seed my tomatoes in a cell tray or directly into 1204 inserts.
Choose a tomato variety or hybrid which has natural resistance to some pathogens. Usually I place one to two seeds in each cell filled with a pre-moistened “soilless” seed germination medium.
Press the seeds into the medium until they are buried ¼ inch deep. Mist with water and place a clear plastic humidity cover over the tray to maintain high humidity while the seeds germinate.
Keep the seed trays between 62-65 degrees Fahrenheit for proper germination. Since tomato seeds do not require light to germinate, they can be placed in a dark germination chamber until the seeds sprout.
Tomato seeds typically germinate within seven to 14 days from being sown.
When germinating seeds indoors it is important not use fertilizers prior to the seeds sprouting. Fertilizer salts can actually inhibit the germination of seeds.
Once germinated, the sprouts can be watered with a half dose of fertilizer for the first week followed by full strength. Make sure you remove any humidity cover soon after germination to avoid dampening off fungi problems from developing.
Page 2 of 2 - Do not be tempted to transplant tomatoes into vegetable gardens too early in the season. Although our last frost date is typically April 15, do not plant your tomatoes outside until at least May 1 if not the 20th of May.
Tomatoes come from tropical South America, and must have soil temperatures above 60 degrees Fahrenheit to maintain their proper growth rate.
Putting tomatoes out too early when temperatures are cool will leave them susceptible to pathogen or frost damage resulting in a crop loss.
For those who are interested, MU-Extension has free “Grounds for Gardening guides on Starting Plants Indoors from Seed” guide number G6570 and Growing Home Garden Tomatoes” G6461.
These guides can be accessed through the search bar on our website http://extension.missouri.edu .