There’s no one universal way to start tomato seeds but here is how I do it.
I use Park Seeds Bio-Dome, a heat mat, and lights.
(I usually use the 40 call planting block for tomatoes, but you could use a 60 cell if you wanted to – the jumbo size is really not needed, since you will be transplanting while the seedlings are young and tender.)
If you do not use the Bio-Dome, with it’s planting sponges, it is recommended that you use an artificial soilless mix for the initial seeding. Regular potting soil has lots of fungi in it and you increase the chances of your seedlings developing damping off which is characterized by the young seedlings developing a narrowed stem at the soil level, eventually falling down and dying. Some people recommend using Chamomile tea to deter damping off, I don’t know if that works or not.
Whether you use the bio dome sponges or a soilless mix, you MUST transplant the seedlings at least once in order to get a decent plant.
I start out by soaking my bio-sponges, then squeezing out the surplus water, so that they are nice and moist to start with.
Now I plant my seeds. I often plant only one seed per sponge. You might want to plant 2, but then you have to thin to one once it germinates. You don’t want two seedlings in the same sponge.
When you are done sowing, put the lid on the Bio-Dome, but leave it open to vent excess moisture to start out. You want to keep conditions moist, but at the same time allow for air circulation so as to not risk damping off. I often prop up one side of the Dome the first couple of days, until the Dome stops being steamy, otherwise you risk literally cooking your seedlings to death.
Once I am done, I set my whole Bio-Dome set up on a heat mat. Do not place under lights until the seedlings have emerged, or you’ll cook your seedlings. Tomatoes do not NEED bottom warmth for germination, as do most peppers, but they will germinate faster that on a heat mat. When you see the first seedlings emerge, immediately I remove the Dome, and set the tray under lights.
The lights must be kept about two inches above the growing seedlings. I think just one inch is even better. It means you’ll have to move the light fixtures often during early growth. It’s hard to grow good seedlings without strong light. If you use a windowsill be sure there are no drafts because cold drafts and wet mix spell doom and death to the seedlings. And you must also remember to turn the container each day so light reaches all sides of the plants. I much prefer growing under lights.
If you planted more than one seed per sponge thin out the young ones – you can do it just by pinching them or use a small pair of scissors. (don’t pull them out, you risk pulling the next one out with the one you intended to remove)
When using the Bio Dome, just add water from the bottom as needed.
With the lights, use a timer. Leave the lights on for 14-16 hours per day and NEVER at night. The plants need a dark period for proper metabolism.
The first little green things that emerge are NOT leaves, they are called cotyledons. They are followed by the first set of leaves and then the second set of leaves at which point you MUST transplant the seedlings to another container as described below.
Occasionally the seed coat doesn’t come off one of the germinated seeds and if you don’t remove it the plant will die. Moisten a cotton ball and hold it to the seed coat for a few minutes. Then gently grasp the seed coat with your fingers and it should slip off. If it doesn’t, you just lost a plant. Because these things do happen, it is always a good idea to plant a few more seeds than you need – that way you won’t be too grief stricken at the loss of one of your babies. If you end up with extras, you will probably have some gardening friends who are happy to get a healthy seedling just in time for planting season.
By the way, once you start raising seedlings, you will realize why so many gardeners refer to their seedlings as “their babies”. When you raise them from seed, you really do form a bond with your plants.
I do not add any fertilizer at all up to this point. When I transplant for the first time, I use an organic potting mix and add organic fertilizer into the mix. I use red plastic cups from Costco. (tomatoes like red, and the cups from Costco I find to be a great size). Some people say no fertilizer at all, I find my seedlings do better with an organic fertilizer – it is mild and won’t burn the seedlings.
When you transplant, you bury the tomato seedling to leave only the top part sticking out over the soil. Why is it so important to transplant? Because it shocks the plant and retards foliage growth so that the plant will focus it’s energies towards root development instead.
If you don’t transplant you end up with huge leggy seedlings that flop over. Also, by burying the plant when you transplant, so just the very top of it sticks out over the soil surface, you stimulate root growth along the buried stem.
Make sure the seedling mix you are going to use is moist. Make a hole to be ready to receive your seedling, then push the bio-sponge out from the bottom and sink the seedling all the way down so that only the little leaves are above the soil line.
Again, I can’t stress enough how important this is. Tomatoes form roots wherever the stems make contact with soil so you want to sink those plants way down. When you finally transplant out into the garden you should do the same thing to make a strong root system.
Now water in the newly transplanted seedlings.
Put your transplants back under the lights keeping the lights no more than two inches, or so, from the leaves – 1 inch is even better. Put your transplants back on the windowsill if not using lights and keep rotating the containers each day so they get even light.
Tomato plants develop best when grown at cool temps. Commercial growers will
usually have one greenhouse set at about 55-60 F degrees. If you can duplicate that you’re going to get a better plant. Warmth is needed for germination and early seedling growth but once you transplant you want cool conditions for optimum plant development. If you can’t, you can’t. Don’t worry too much about it. I keep mine in the garage after the seedlings have emerged.
You keep growing your plants until they get to be maybe about 10 – 12 inches high and it should be close to when you want to transplant them outside.If you want to run a fan near your growing plants that’s fine also; good for air circulation. And if you want to run your hands or a ruler over the foliage a couple times a day that’s fine too. The plants respond well to touch, that is sometimes reflected in even better growth.
Before planting out, you must harden off the seedlings. That means putting them outside for a few hours each day , initially in a shaded spot, and then increasing exposure to the sun as the days pass. Protect from harsh winds and bring the plants inside if the weather gets too cool. The seedlings must be hardened. During this period, don’t water the seedlings too much either. Don’t water them until they are on the verge of wilting.
If your plants start forming blossoms prior to transplanting out in the garden, remove every single blossom on the plant. The earliest growth of a tomato plant must be devoted to vegetative grwoth of leaves, stems and roots, not a sexual cycle of reproduction and setting fruit, etc. So get all those blossoms off the plants. Blossoms that develop once the plants are out in the garden are fine to leave on the plant.
Choose a spot for your tomato plants that get the maximum amount of sun, and where AM sun will burn off the early morning dew, this is important for disease prevention.
Transplant out to your garden when the risk of frost has passed. Remove any leaves of the plant that have turned yellow. It’s natural that the leaves towards the bottom of the plant would have turned yellow and most of the time those yellow leaves will fall off naturally. If not, you take them off. Now dig a horizontal hole, long enough to hold all but the tip of the plant. Lay the tomato plant down sideways in the hole, and allow just the very tip of the plant to peek out above the soil. Laying them sideways allows you to bury the whole stem while still keeping at a warmer layer of soil. Don’t be discouraged at how very tiny your seedlings look right after transplant, it’s supposed to be that way, and in no time at all they will grow up to be strong and sturdy plants.
After transplanting to the garden water them in well.
At transplant time, I again add organic fertilizer, right into the planting hole. (be aware that I garden organically, if you use chemical fertilizers, don’t follow my advice on fertilizing, you will probably end up burning the roots.)
Note in the photo above, that very little of the seedlings are above ground, compared to the photo of the seedlings above, just prior to transplanting into the garden.
Thanks to Dr. Carolyn Male for providing the guidance for me as I learned to start my tomato seedlings – though I have modified her method, especially as regards use of fertilizer, and she would NOT approve the above. Nevertheless, her instructions were invaluable to me as I got started with growing tomatoes from seed, and she should get credit for teaching many new gardeners the joy of raising tomatoes from seed. The method described here works for me. Probably every person raises their seedlings a little differently – you have to find out what works for you.
Seeds should be started 6-8 weeks before the last average frost date. I tend to start mine about 2 months before the last frost. Perhaps these instructions can serve as a guide for you to get started by.