By now you should have started your tomato seeds indoors under lights. This is just if you want a head start of course, it is not necessary. You can also purchase tomato plants but be aware that the night temperatures are still cold for them to be out in the garden now. They prefer warmer weather. Waiting to plant tomatoes until the beginning of May or Mother’s Day will give you the best results. For tomato success, read these twenty tips for growing tomatoes in the Washington DC metro area.

First, know what you grow. Tomatoes have determinate or indeterminate growth habit. Determinate types produce fruit at the end of the branches so most of the crop ripens at one time and you will have one or two harvests per growing season. This is advantageous for canning. The determinate types are more compact and are better for containers than the indeterminate tomato plants; however, you may still have to stake the vines or add a trellis. Indeterminate plants produce fruit along the branches so you can pick tomatoes all season long. They can be large, vining plants; a support system such as hoops or stakes should be used.

Sun Dipper, from PanAmerican Seed Handpicked Vegetables.

2. Tomatoes come in many sizes, shapes, colors, and flavors. Grow what you like to eat or use in the kitchen. For example, determine if you prefer to use tomatoes for salad, snacking, pasta sauce, sandwiches, etc. There are more specialized varieties for specific uses such as the Sun Dipper pictured to the right which is elongated to make it easier to hold while dipping into a dip.

3. If you are limited to containers, grow the determinate type and use a container at least 5 gallons large with drainage holes or an Earthbox. Or look for varieties especially bred for containers such as window box types (usually these will be the small, cherry types).

4. Determine if growing an heirloom plant is particularly important to you. Heirlooms may be tastier, and seeds can be saved for next year, but these plants may be more susceptible to diseases. Hybrids are often bred to be disease resistant. However, if you save and sow the seed next year, the plants may not have the same traits as before. Seed catalogs and packages often have letters after the plant’s name to indicate disease resistance. For example, F is for fusarium, V for verticillium, LB for late blight, TMV for tobacco mosaic virus, and N for nematodes.

Early Girl gives you fruit earlier than most other tomato plants, photo courtesy of Ball Horticultural Company

5. Days to maturity is the number of days it will take on average for a transplant to produce a tomato (fruit) when planted in the beginning of the summer. It is not the number of days from seed. This varies quite a lot with tomatoes from plants with a lower number of days which will provide an early season harvest, to mid-season, to those with larger numbers, resulting in a late season harvest in late summer. If you have the space and want tomatoes throughout the growing season, you can plant early, mid, and late season plants.

6. If starting from seed, sow seeds about a month before average last frost date (Mother’s Day here). Start inside under lights. When the seedlings produce a set of true leaves, you can pot up the plant into a larger container and put outside for a few hours a day. Gradually introduce seedlings to more daylight and more time outside in order to harden off before putting in the ground. Hardening off is the process of acclimatizing seedlings to higher light levels, cooler (than your home) temperatures, and breezes so they can withstand being outside. Here is a link to tips for starting seeds indoors.

7. At first the nighttime temperatures may be too cold (forties and below) to leave these transplants outside so you may have to bring the pots inside for the night.

8. Seedlings and transplants in the spring may develop purple tinged leaves which means cool temperatures are preventing phosphorus absorption. In the summer, when it gets warmer, they will grow out of this so no need to do anything.

The purple coloring on Indigo sun tomato is intentional, it is a higher level of anthocyanins, which is healthy for you, photo courtesy of Ball Horticultural Company

9. Tomato plants need at least six hours of sun and like warm soil, which is why it is best to put the transplant in the ground after Mother’s Day. If you plant them in cold soil, they will sit, unhappy.

10. Tomatoes like fertile, well-composted soil, not clay. In this area, you may have to amend your garden bed with compost. In the spring, a raised bed and a container will have warmer soil than the ground.

11. When nighttime temperatures are in fifties and the transplant is hardened off, plant in ground. For the indeterminate types, insert staking or hoops immediately after planting. Make sure you have spaced your tomato plants so there is a minimum of 2 feet apart for air circulation (to decrease a pathogen’s ability to spread).

12. Tomato stems will develop roots if covered with soil. Some gardeners will bury as much stem as possible to encourage root production. The theory is that if there are more roots, the plant will be able to take up more water and nutrients. Some people lay the transplant down on the ground, horizontally, burying the stem, but leaving 1 to 2 set of leaves above ground. Some people plant vertically, but very deep, leaving 1 to 2 sets of leaves above ground. Before you submerge the stem, strip off the leaves and little branches that would be underground.

13. A lot of gardeners add calcium in the form of crushed eggshells to the soil or 1/4 cup of lime before planting to prevent blossom end rot. If you do not do this, then pick a fertilizer especially formulated for tomatoes because it should have the added calcium.

14. In the beginning of the summer, mulch with straw, leaves, or compost to prevent weeds and to keep a constant level of soil temperature and moisture. Try Maryland’s Leaf-Gro; do not use composted manure.

15. Tomatoes will need to be watered so make sure a hose or watering can is available. Water the soil, not the plant, and water in the morning to decrease possibility of fungal disease. It isn’t that tomato plants need a lot of water, it is that the soil moisture must be consistent, and not fluctuate often. Mulching helps with this.

Think of how much water, sun and fertilizer it will take to produce this large slicer, Beefmaster. Photo courtesy of Ball Horticultural Company.

16. In mid-summer, tomatoes will need to be fertilized, especially if grown in containers. Espoma has organic Tomato-Tone and Neptune’s Harvest has a Tomato and Vegetable Formula.

17. To obtain fruit, temperatures must be above 55 degrees at night but temperatures of 75 or higher will inhibit fruit set and may cause blossoms to drop. However, there are heat-tolerant varieties.

18. Tomatoes are wind pollinated. Some gardeners hand-pollinate with a paintbrush if they feel the plant is not setting fruit. All the more reason why there should be good air circulation. Harvest frequently to encourage plants to produce fruit.

19. Pruning is optional, but only indeterminate plants should be pruned. Pruning here refers to removing the side shoots or suckers. Some gardeners do this to increase or to have more uniform fruit size and to help tomatoes ripen faster. It will not increase the number of tomatoes. If prune, start when plants are about 2 feet tall and suckers are small. Do this when the plant is dry, not wet from rain.

20. If possible rotate crops to prevent soil-borne diseases. If your tomato plants are having problems, check out the Virginia Tech Extension site on growing tomatoes, tomato diseases, and tomato pests; and the University of Maryland Extension site on tomato diseases, pests, and nutritional issues, growing tomatoes, and tomato topics; or contact your local extension agent.

21. Pick the fruit when it begins to color and bring inside. Ripen at room temperature and do not put in the refrigerator. This also prevents animals from eating the fruit before you do.