The typical summer weather pattern in the Central San Joaquin Valley begins with the formation in late April or early May of a high pressure ridge or dome that traps hot, stagnant air and lowers humidity.  This year dangerously high temperatures and dry conditions did not develop until the Fourth of July holiday.  Some weather forecasts are anticipating high temperatures with very hot days and nights to be continuous for at least the next two to three months; heat spikes with several consecutive days of extremely high temperatures can also be expected.

Hope for the best; prepare for the worst.’ Central Valley gardeners struggle to mitigate the effects of heat stress, low humidity and air pollution on plants every summer growing season.  Some of our practices will need to change or be modified in order to keep plants alive and healthy as overall temperatures rise and weather patterns change.  Water conservation is always a concern.  

Deep, infrequent irrigation to encourage root development at deeper levels in the soil is still advised during periods of less intense heat.  We’ll still need to keep automatic sprinkler systems on the mandated schedule but increase watering times.  However, we now need to begin deep irrigation of vulnerable plants several days before heat spikes are predicted to arrive.  Use soaker hoses, bubblers on a hose or small oscillating sprinklers to slowly irrigate the soil under the most vulnerable or productive plants to a depth of 8 to 12 inches. Test soil moisture levels frequently with the goal of keeping the soil consistently moist.  Most plants will need to be watered in summer when the top inch or two of soil has dried.  That maybe a daily or even twice daily occurrence during heat spikes.   

Plants that produce crops (fruit and nut trees, summer vegetables, roses) need replacement nutrients as crops are removed.  Fruit and nut trees should be fed after harvest with high nitrogen fertilizers.  Harvest of fruits and nuts may come sooner than usual as temperatures rise and crops ripen quickly.  Summer vegetables are another story.  Tomatoes, cucumbers, beans and squashes will stop producing flowers when temperatures are above 90 degrees. Mediterranean varieties of those plants tend to be more heat-tolerant.  Heat-loving peppers and eggplants will continue to produce and hold flowers at higher temperatures.  

If your plants are holding their flowers and the fruit continues to develop feed lightly with a low-number, low-nitrogen fertilizer once a month.  Stop feeding summer vegetables and annual summer-flowering plants if all the flowers or the immature fruit have dropped and resume feeding them when new buds begin to show.  Some gardeners continued to put in transplants in May and June, well after the end of the normal summer planting season.  The new transplants with immature root systems will be unlikely to survive the first heat spike of July even when well-watered.