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Growing Tomatoes in Napa County

By Dean Donaldson, Farm Advisor

 Kinds to Plant:

Tomato plants produce a wide variety of fruit size and color from bush and pole types. There are 100's of named varieties available to home gardeners.  Local trials and taste panels of Master Gardeners suggest growing varieties that are suited to our coastal growing conditions, some reliable varieties are: Better Boy, Bragger, Celebrity, Champion, Early Girl, Quick Pick, Sweet 100, Sun Gold, Supersteak, Whopper and Yellow Pear.


Tomatoes are injured by frost and require moderately warm to hot weather to produce a crop.   Cool night temperatures and temperatures over 90ºF may cause flowers to abort.  Tomato plants require warm soil, over 60ºF, deep irrigation and full sun exposure all day, 6-8 hours minimum. Temperatures below 57ºF delays growth and aids diseases, best range is 80-90ºF.

Soil Preparation and Planting:

Plant after frost mid April through May. Tomato roots can grow to 4 feet deep in good soil. Planting deep, by digging a deep hole and planting the plant about half way up the stem (remove leaves for underground parts). Plant will grow root out of stem joints and thus create a bigger root system. Plant tomatoes into a bed after a winter legume cover crop to increase the soil fertility. Tomatoes are moderate users of Nitrogen and Phosphorous, so pre-plant fertilizer should include manure or a commercial fertilizer. Use 10 pounds of dry manure or 1/3 pound of commercial 12-12-12 fertilizer per 10 square feet of garden. Mix fertilizer or manure thoroughly into the top 3-6 inches of soil before you plant.  Transplant seedlings into the field after they are ‘hardened-off’.   Set plants two feet apart in rows three feet apart. Water-in to settle the soil around the transplants.


Care and Harvest:

Tomatoes ripen after about 85-100 days, depending on weather and variety. Tomatoes like deep watering once per week to wet at least 3 feet deep.  An additional application of Nitrogen fertilizer during bloom will prolong fruit production. Give extra water during ‘hot spells’. Harvest fruits regularly to assure continued production. Cool wet fall weather will signal the end of harvest. Pink fruit will ripen on the shelf, but fully ripe red fruit are much sweeter.


Common Problems:

Two caterpillars and several sucking insects can injure developing flowers and fruits.   Watch for caterpillars after mid summer.   Regularly inspect under leaves or on fruits near ‘spotting’ (manure) from caterpillar feeding.   Control with suitable pesticide or remove by hand.   Prevent ‘Blossom End Rot’ of fruits by deep digging before planting and by additional deep watering during hot weather. Curled leaves are common to some seed lines but do not impact plant growth or fruiting.   Cool nighttime temperatures cause flowers to abort, and plants are easily injured by frost. Remove and destroy rotted fruit to avoid spreading fruit diseases. Rotate tomatoes with corn, beans and leafy vegetables.


Plant late into warm soil and give deep water. Give extra water during very hot weather. Mulch soil surface with clear plastic for faster harvest. A repeat planting after 4 weeks will extend home harvest period most years.

 Additional Reading:

Integrated Pest Management for Tomatoes, UC ANR Publication #3274, 4th Ed., 1998; Home Vegetable Gardening, UC ANR Publication #21444, 1992.

 March 2011