It's Time to Plan Your Summer Tomato Crop

Mar 6, 2023

Photo of plants for sale

It is not unusual to find tomato seedlings for sale in local nurseries and big box stores as early as February or March. Don't make the mistake of rushing to plant them in your garden. In our County it is much too early to put tomato seedlings in the garden, but it is the perfect time to make plans for a bumper summer crop of garden-ripened tomatoes.

When should you plan to plant tomato seedlings in the garden? The easiest way to determine when it is time to plant is to check the soil temperature. The soil should be no less than 60º Fahrenheit when you transplant tomato seedlings. When soils will reach that temperature will depend not only on the climate of the garden location but also on soil type. Sandy soils will warm sooner than clay soils, and soil or potting mixes in containers and raised beds will warm more quickly than soils of in-ground garden beds.

To check, use a thermometer—a soil or kitchen type both work--and measure the temperature at a depth of four inches below the soil surface. Check early morning when the soils are at their lowest temperature. The soil temperature will reach and maintain at least 60º F only after daytime highs are reliably in the 60's and overnight temperatures don't fall below 50º. In Contra Costa County those temperatures generally are achieved late April or early May. If you transplant seedlings by the end of May, the plants still have time to produce well.

So, you still have at least two months to get ready to plant tomato seedlings in your garden. Use that time to decide which tomato varieties you'll grow to get the best results. Two important topics to consider are identifying varieties that will grow well in your local climate and choosing varieties with resistance to diseases that may have been a problem in prior years.

If you live in a cool, foggy or windy climate, choose varieties with shorter “days to maturity”. “Days to maturity” is the estimated time the tomato variety will take to start producing harvestable tomatoes after seedling transplant to the garden. Tomatoes requiring 75 or fewer days are more likely to produce crops in cool climates than those with longer maturity. Most cherry tomato varieties need less than 75 days to start producing, and you can also find some “slicer”,” paste” and “beefsteak” tomato varieties that reach maturity in 75 or fewer days.

If you live in the hot, dry climate found in interior areas of our County, look for varieties with good heat tolerance. They may include both varieties with short days to maturity and those with longer maturities. An internet search for “tomatoes for hot, dry climates” will identify sites with lists of tomatoes well adapted to grow and produce in such conditions.

If you have had disease problems when growing tomatoes in your garden in prior years, try to determine which disease was present. These links provide information that you can use to diagnose and manage common tomato diseases and other problems: (Managing Pest in Garden) and (Tomato Growing Tips).

Often disease pathogens remain in the soil long after diseased plants are removed. If you've had disease problems, grow your tomatoes in a garden bed where you haven't previously grown tomatoes or other members of the Solanaceae (nightshade) plant family such as peppers, eggplants and potatoes. If your garden area is small and you don't have a disease-free planting area, grow your tomatoes in large containers or plan to plant hybrid varieties instead of heirloom varieties.

Heirloom tomatoes are “open pollinated” varieties that are grown from seeds passed down for more than fifty years. Seeds from open pollinated varieties grow plants that are a genetic match to those of the parent plant. A shortcoming of heirloom tomatoes is that they rarely possess resistance to common tomato diseases.

Hybrid tomatoes are varieties that are created by intentionally cross-pollinating two or more tomato varieties to achieve desired characteristics which may include disease resistance. Seeds from hybrids won't produce matching tomato varieties, so don't bother to save their seeds. If you have identified a disease that has caused problems in your garden, choose tomato varieties with resistance to the disease. Seed packages and descriptions of tomatoes in seed catalogs typically include letter codes to indicate any disease and pest resistance. Common codes include:

  • V: Verticillium wilt
  • F: Fusarium wilt; a code such as FF or FFF indicates resistance to multiple strains
  • T: Tobacco mosaic virus
  • A: Alternaria
  • EB: Early Blight
  • LB: Late Blight
  • N: Nematodes (not a disease but microscopic worms that feed on plant roots

If you don't know the disease resistance of a tomato variety you want to grow, you can likely find it on this Cornell University website: You may not find tomato varieties with disease resistance to all tomato diseases. For those diseases, be sure to check the UC websites referenced above for tips on managing the disease.

Once you have identified tomato varieties you would like to grow, check with your local nursery to see if it plans to carry them. If you plan to shop the Great Tomato Plant Sale (GTPS) sponsored by UC Master Gardeners of Contra Costa County, you will find a list of tomato varieties that will be available at If you aren't sure your targeted varieties will be available locally, it's not too late to order seeds and start your own plants. It will only take about six weeks from the time you plant seeds to have seedlings ready to transplant to the garden. Stay tuned for our next blog post to get tips for caring for seedlings and transplanting them to the garden. And mark your calendars for the GTPS which will be held “in person” at the Walnut Creek Our Garden location on April 1, 2, and 3 and at the Richmond Library on April 29.

photo credit: Terry Lippert

Help Desk of the UC Master Gardeners of Contra Costa County (TKL)