Prepping the Garden for Tomatoes

Where you plant your tomatoes in the garden is important. Tomatoes need at least six to eight hours of sun a day to produce well — and full sun is best, especially in cooler, more northern climates. Tomato roots won’t do well in soggy soil — a sunny, well-drained part of your garden is best.

Best Soil for Tomatoes

Tomatoes like their soil pH around 6.0 to 6.8. Briefly, pH is a measure of soil acidity or alkalinity. On the pH scale, 7.0 is neutral; so the range which tomatoes prefer is slightly on the acid side. (By the way, that’s the pH range at which most vegetables grow best.)

You should check the pH level in your garden every three to five years. You can test it with an inexpensive kit from a garden center, or your local cooperative extension service may offer an inexpensive testing service.

If your soil pH is too low (too acid), you’ll need to add lime to the soil to bring the pH back into the proper range. Gardeners in western states (and some areas of the east) often have high pH or alkaline soils and may need to add sulfur to the soil to lower the pH. Although lime and sulfur can be added to the soil any time the ground isn’t frozen, fall is a convenient time for many gardeners and gives slow-acting lime a chance to take effect. Get recommendations from the Extension service on how much lime or sulfur to apply based on your soil test report.

Making Better Soil

No matter what kind of soil you have in your garden, you can shape it into a great home for your tomatoes with a little work. Both light, sandy soils that drain too rapidly and heavy, clay soils that take forever to drain and warm up in spring can be improved with the addition of organic matter — leaves, compost, grass clippings, garden residues or easy-to-grow cover crops such as buckwheat, cowpeas or annual ryegrass.

In sandy soils, organic matter builds up the soil’s water-holding capacity. This is vitally important for tomatoes, which depend on a continuous supply of moisture all season long. But tomatoes don’t want to sit in puddles! Organic matter also opens up the heavy soil so that water and air penetrate better.

If your tomato crop has been only so-so for the past few years, work some extra organic matter into the soil where your plants will be growing. You’ll probably see a big difference in the harvest.

Before transplanting tomatoes, it’s a good idea to work the soil until it’s loose to a depth of six to eight inches. You can do the work with a tiller or a garden fork. The tomato roots will be able to expand quickly in the loose earth and you’ll also uproot and kill many weeds.


It’s important to work some fertilizer into the soil at transplanting time so that your transplants can get off to a good start.

After the soil has been well tilled and is loose, make a trench or furrow six to eight inches deep down what will be the row of tomatoes. At the bottom of the furrow put a thin band of organic or chemical commercial fertilizer, such as 5-10-10. The numbers 5-10-10 refer to the percentages, by weight, of nitrogen (N), phosphorus (P) and potassium (K) in the bag of fertilizer. They’ll always be listed in that order, too: N-P-K.

Another method is to put down a deeper band of dehydrated animal manure, compost or rotted leaves. You can use both methods for a quick start and strong finish for your tomatoes.

Then, no matter which method you’ve chosen, cover all this fertilizer with two or three inches of soil. If your transplants’ roots or stems come in direct contact with the fertilizer, the salts in the fertilizer can draw moisture from them, which is harmful. If the fertilizer is deep underneath the plant, the roots will grow to it and absorb the nutrients gradually.

After covering the fertilizer, it’s just a matter of transplanting the tomatoes into the 3- to 4-inch-deep furrow.

Deciding when to transplant tomato seedlings is easy. When tomato seedlings are three or four inches tall and have their second pair of leaves, it’s time to take them out of their crowded containers and put them into deeper, roomier ones. (If you started seedlings in individual containers at least three inches square, simply thin out the weaker plants by snipping them off at the soil line and leaving the strongest one.)

Choosing The Right Container

Any part of the tomato stem that’s covered with soil will develop roots, and a large root system is important for transplants. Try using a deeper container and set the plants lower than they were growing before – right up to the lowest set of leaves if you can. Use the same soil mix that you used to start your seeds. Here are some hints for successful repotting:

  • Water the tomatoes well before you start to repot. Moist soil will cling to the roots and protect them from drying.
  • Lever the seedlings out of the soil with a small utensil, such as a table knife. Lift the plants by their leaves, if necessary, rather than by their stems – if you lose a leaf, it can grow back, but if you break the stem below the leaves, the plant won’t make it.
  • Set the seedlings about three inches apart in their new container(s). Firm the soil around them, and water gently. Keep out of bright sunlight for a day or two.
  • Fertilize once a week with liquid fertilizer. Follow the directions for dilution on the label. Some recommend different dilution and application rates for seedlings versus houseplants or full-grown plants.

The Second Transplant

Before the tomato plants can be transplanted successfully to the garden, they need to develop strong root and top growth. To be sure their seedlings have a good root system, many gardeners prefer to repot them a second time before setting them out in the garden. Wait until seedlings are six to 10 inches tall. A good rule is to transplant when the height of your seedling is three times the diameter of its pot. Pot them up individually in half-gallon milk cartons or four- to six-inch-diameter pots. Again, you can plant them right up to their first set of leaves.

Indoor Care

If your seedlings are getting tall and spindly, the room temperature may be too high, the light too weak, or you’re using too much fertilizer (or a combination of all three). Review seedling needs in Starting Tomatoes from Seed and adjust growing conditions as needed. Transplanting leggy seedlings deeply helps them to root along their stems, thus reducing the problem, but the best solution is to give your young plants proper growing conditions in the first place.

Starting Tomatoes from Seed

Starting tomato seeds is quite easy. Follow these basic steps for growing healthy transplants.

1. Start with a bagged seed starting medium or fluffy potting mixture. (Heavy potting mixes may stay too moist and reduce germination rates.) Moisten the mix to the dampness of a well-wrung sponge, fill your seedling tray or individual containers, and, and firm the surface.

2. Sprinkle the seeds on top of the soil, about 1/2 inch apart in flats (where they can be scattered over the surface or placed in rows), or sow two to three seeds per individual container.

3. Firm the seeds into the soil with a small piece of wood or other flat objects. Then put a thin layer – about 1/4 inch – of moist soil mix over the seeds and then firm it again. This brings the seeds into good contact with the soil, which is important for germination.

4. Place the container inside a plastic bag or cover it with a sheet of plastic or a plastic tray lid to keep the soil mix from drying out.

5. Put the container in a place where the temperature remains steadily around 70oF. Warm soil is more important than warm air for optimum germination, so providing heat from below really helps. Many gardeners find that the top of the refrigerator is an ideal spot for germinating seeds.

6. The seedlings will begin to emerge in a few days. Check daily and remove the plastic at the first sign of green, then move the container to a well-lit location. A sunny window will work, but a fluorescent light is better. If you use lights, set the plants an inch or two below the tubes and maintain that distance as the plants grow. If the distance is too great, the plants will stretch towards the lights and develop thin, weak stems. Keep the lights on 14 to 16 hours a day, but turn them off for the night. Plants need a rest, too!

7. Provide your seedlings with daytime temperatures in the range of 60oF to 75oF, and night temperatures in the range of 60oF to 65oF to encourage sturdy, stocky plants. Too much heat can encourage leggy, weak growth. Even fluorescent lights can create quite a bit of heat, so check daily to make sure temperatures don’t get too extreme for seedling health. If you need to cool things down, set a fan on low speed near seedlings. (The “wind” also helps seedlings to grow stockier.)

8. Keep the soil moist, but not wet. Water gently so you don’t disturb the soil and expose seedlings’ roots. Use room-temperature water if possible.

9. Don’t worry about fertilizing the seedlings right away. Some commercial seed-starting mixes have fertilizer mixed in that will take care of the seedlings’ nutritional needs until after they’ve put on their second set of true leaves. Wait at least a week (or even until after the first repotting) before feeding seedlings. Then apply a fertilizer diluted to label directions.

Many gardeners transplant their tomato seedlings to larger containers at least once while they continue to nurture them indoors. This makes for larger and stronger root systems.

Hardening Off Tomato Transplants

One of the most important steps in planting comes before seedlings get near the garden. This is the process of hardening off or gradually acclimating your tomato seedlings to outdoor conditions. These plants have spent their short lives in a warm, sunny, protected place and won’t fare well if you don’t expose them slowly to the elements.

A few days before you’re ready to begin hardening plants off, reduce the amount of water you give them, and cease fertilizing until they are planted in the garden.

About 10 days before you intend to plant, put your transplants outdoors in an area where they’ll be protected from the direct sunlight and wind. Leave them out for a few hours and bring them back inside. Repeat this each day, gradually increasing the amount of time they’re outside and the degree of exposure to sun and wind. After a week or so, leave the transplants out overnight. If frost threatens, bring them indoors.

If you harden off your plants properly, they’ll be strong and able to withstand full sun, strong breezes, and all the challenges they’ll meet in the garden.