Growing Tomatoes: Step 2 (Growing from Seed)

Posted in - Gardening on May 30th 2010 0 Comments Growing Tomato Seeds

Purchasing Seeds

For information on choosing a variety of tomato to grow, see: Growing Tomatoes: Step 1 (choosing).

You should acquire your seeds from a reputable source. As tomato seeds age, their chance of germinating decreases. If you are buying seed, make sure to use seed that is less than 4 years old, (seed that is much older can usually be germinated if it has been stored in cool, dry conditions).

Choosing Soil

Soil from your garden is not a great choice for starting seeds because it compacts to easily and can harbor organisms that may cause diseases.

Look for a commercial seed starting mix (or make your own mix of equal parts peat moss, cermiculite and perlite). Some recommended commercial mixes include Jiffy Mix, ProMix, MetroMix and Fafard.

Selecting Containers

Tomato seeds will grow well in any container as long as they receive good drainage, warmth and moisture. An affordable and popular container is the styrofoam or plastic cup with holes poked in the bottom. You can also purchase flats with planting inserts if you are growing large quantities of plants. Note: If you use containers that have been planted before, make sure to sterilize them with a small amount of bleach and water.

Determining When to Start

It is very important to start your seeds at the proper time. If the plants are moved outdoors too late, your tomatoes may not grow properly; the same goes for planting outdoors too soon. Most tomato seedlings are ready to be transplanted within 6 to 8 weeks. In most areas, transplanting should be done about 1 or two weeks after the last expected frost. You can find information from almanacs or on the internet about your area’s last expected frost. You should determine when your plants will need to be transplanted, and grow your seedlings according to that schedule. Also remember it takes about a week to ‘harden-off’ your seedlings for transplant.

Planting Seedlings

Combine your starter mix with warm water. It can be difficult to moisten dry mix, so gardeners often let it soak in water overnight. The final mix should be damp, but not soggy or dripping.

Fill your containers with the damp mix and plant your seeds about 1/8 of an inch deep (you can use a pencil to make the hole). Cover and gently firm the soil over the seed (this is important because the seed needs to be in direct contact with the soil to absorb moisture).

If you prefer, you can plant seeds fairly closely together at the start because you will be transplanting them to larger containers after their first ‘true leaves’ appear.

It is best to provide plastic cover during the early growing stages to hold in humidity and moisture. You can use plastic bags or a sheet of plastic (allow for some air to circulate, but don’t let the mix dry out).

Germination Stage

You will want to place the containers in a warm place (70F to 80F) that is out of direct sunlight (to avoid drying the mix too quickly).

As soon as the seedlings emerge you will need to move them to a light source. Growing seedlings indoors will require a strong fluorescent shop light. South facing windows can sometimes work, but may not provide the strength and duration of light you need to give seedlings a good start.

If you choose to use a shop light, you will need to find a way to keep your seedlings within several inches of the bulbs for at least 16 to 18 hours a day.

Once the seedlings have emerged, they grow best at a temperature of around 65F with good air circulation and lots of light. Most growers will water the plants by soaking them heavily and letting them get nearly dry before soaking them again.


When your plants have developed their first true leaves, you will want to re-pot them into larger containers. This step is very beneficial to the plants because it encourages growth of a stronger root system.

If your starting mix does not have any fertilizer, you may need to add small amounts of it during the germination and growing process (if you do, dilute it heavily and use very small amounts).

Depending on your container sizes and growing conditions, you may be required to re-pot them again before transplant occurs, keep and eye on the plants (if the roots are growing to the edges of the pot and binding up, you will want to move them again).

If you planned your transplant date well, you should be able to move your plants before they become too large to handle.

Hardening Off

To “harden” your plants, you will need to allow at least a week for slow adjustment to the outdoors. Start by bringing them outdoors in a dappled shaded area where there is protection from wind and strong sun, and bringing them back in at night. Slowly progress to more time in the sun and wind and eventually leave them out at night (if threat of frost is nigh, bring them back in!). You can build your own temporary structures to protect seedlings during this hardening off stage, or you may already have a great location in mind.

Many believe it is best to pluck off early blossoms on plants before transplanting (this is an optional step).

Recognizing Problems

Leggy Seedlings: If your seedlings become very tall and limp with sparse foliage, they are probably not getting enough light. You may end up having to start over completely, or you can try re-potting them deeper to cover some of the weakened stem (and then providing a stronger source of light).

Damping Off: If plants are not germinating or they sprout up and then fall over, you are most likely witnessing a case of Damping Off. This is usually caused by fungi, and is found to be problematic when people use soil straight from the garden to start their seeds. If you purchased commercial mix and are still experiencing this problem you may want to consider a different mix next time. NOTE: Having your plastic sealed too tightly (not allowing for any air circulation) can also cause this problem.

Slow Growth: If your seedlings just refuse to grow it probably has something to do with the temperature being too low, seeds being too old or improperly stored, or nutrient levels not being high enough in the soil.

Stuck Leaves: Sometimes the first leaves will get stuck in the seed coating as they emerge. Usually this will fix itself, but you can gently mist with a spray of water to help loosen the seed coating.

Over-Watering: This is the most common issue beginners experience: Over-watering will cause your seeds to rot. Do not allow the soil to become soggy during germination. After the seeds have sprouted, allow the soil to become nearly dry (and even allow plants to wilt slightly) before giving it a good soak again.

Over-Fertilizing: Over-fertilizing will cause seedlings to die, stop growing, or grow too tall and leggy. One application of highly diluted fertilizer is usually more than enough to get a seedling through to transplant (you probably don’t need any if using a commercial mix).

Harvesting Your Own Seeds

You may have plans to harvest your own seeds and use them next year. If you intend to harvest and regrow your own seeds, you should avoid hybrid varieties because they are not as likely to produce good crops down the line. Heirloom or open pollinated varieties are your best bet for seed harvesting success.

Because some varieties of tomato can be cross pollinated naturally (by wind or insects), you will need to begin your seed harvesting steps before the blossoming and fruiting stage of growing.

First, you will want to choose a branch (or several) with flower buds that have not opened yet. Carefully cover the buds with cheesecloth to keep bugs and pollen from accessing them. Once the fruits begin to develop, you can remove this cover and tie a piece of yarn or string on the branch so you remember where to harvest your seeds from.

Once the fruit is thoroughly ripened, you can remove it from the branch, and harvest the seeds.

Fermenting Seed

Wash the tomatoes and cut them through the center (do not cut vertically through the stem, cut across the center of the flesh). Gently squeeze the center core and seeds into a container and be sure to label it with the variety and date. Fill the container half-way with water.

Cover with a piece of thin cloth and sit in a dark warm area for 3 to 5 days. The liquid should form a thin layer of white mold. Carefully spoon off this mold, fill the container with water again, and stir. The good seeds should sink to the bottom.

Remove the bad seeds and then strain your good seeds through a fine strainer. Place these seeds on a single layer over a plate and let sit for another 3 days to dry.

Put in a labeled envelope or jar and store in a cool, dry place till next year.


Comments are closed.