Water Tips for Gardening in Very Hot Weather

Sep 18, 2023

This last year of unpredictable weather of up and down temps, hot and cold, some rain and dry weather, did not bode well for this gardener and maybe not for others.

In my neck of the woods of the San Joaquin Valley (Stockton), spring began with cooler-than-normal weather as well some on-and-off rainy, windy days. Should I plant seeds or start with nursery plants? With the crazy weather in early spring, I thought, should I even start to plant anything at all? What's a gardener to do?

After a few weeks and warmer weather, I decided to pick up a few young plants and begin my summer garden in my raised garden boxes. My harvest has been limited: only a few watermelons, a handful of tomatoes but loads of squashes, of course. While still small, several melons busted open showing a less than desirable melon. My watermelon crop yield has been only a few in a raised bed of mostly vines that started as a great display of beautiful green leaves with lovely little yellow flowers that I looked forward to becoming large, glorious watermelons. What resulted was a bed of greenish-gray leaves without flowers and only a few sweet, edible melons.

What I've learned this year is that as temperatures rise beyond 85°, the growth rate of plants slows down due to photosynthesis, the process in which plants use the sun's energy to create carbohydrates as a food source reduces when temperatures rise into the 90 and 100 degrees.

In contrast, the rate of respiration (the process by which plants use carbohydrates to grow and develop) continues day and night, even at higher temperatures.  This depletes the food reserves of the plant. If extreme heat continues for weeks at a time, as it has this year, plants can actually die from a depletion of their food reserves. 

High temperatures can also cause severe water loss (desiccation) when transpiration (the process by which leaves release water vapor to the atmosphere) exceeds moisture absorption by the roots. Evaporation of water from the soil can further reduce the amount of water available to plants.

So, what to do in extreme heat to protect not only your garden, but also lawns and landscape? Below are some suggestions and information to help us all better understand the impact of the predicted long-term hot weather on our gardens.

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Change Irrigation Routine

High temperatures will result in higher water loss both through the leaves of the plant (transpiration) and through evaporation from the soil surface.

  • Check soil moisture at least daily – When soil is dry at a finger's depth or more, it's time to water.
  • Water in the morning - Less water is lost to evaporation in the cooler early part of the day and allows plants to fully hydrate before temperatures rise. Early morning watering will also allow wet foliage to dry quickly in the morning sun. Morning watering also ensures plants are fully moistened as the day gets warmer.
  • Water the root zones, not the foliage. Roots absorb the water. Wet foliage is more susceptible to disease.
  • Apply water efficiently - High temps mean more water evaporation before it reaches the roots.  Instead of sprinklers use spot watering at the base of the plant, soaker hoses, or drip irrigation systems to provide water efficiently.
  • Water slowly, deeply, and infrequently. Avoid a quick splash that can cause shallow rooting and lead to poor drought tolerance.
  • Apply water until the soil is moist to at least 5 to 6 inches. Unsure how deep the water penetrates, dig a hole to see for yourself. Only apply water when the soil is dry to the touch 1 to 2 inches deep.
  • Use mulch to conserve soil moisture and reduce watering frequency. Mulch can be used in most settings including veggie gardens and containers.
  • Plants in containers and hanging baskets may need water twice a day - especially when weather is windy and hot, containers dry out very quickly.  Check often, as most will need water at least once a day, and some may need water in the morning and the evening.
  • Check on recently planted plants.  Perennials, trees, and shrubs planted earlier in the year have not yet been rooted in fully.  With most roots still in the original root ball, that root ball can quickly dry out.  Check newly planted plants frequently, and water both the original root ball and the surrounding soil if either is dry.  The same consideration is important for those plants planted within the last three years.  These plants still do not have extensive root systems and may need extra water during stressful times.
  • Always check soil moisture before watering.  The metabolic processes (photosynthesis, respiration, and nitrogen fixation) slow down in extremely hot temperatures.
  • If you'll be out of town for a couple of days, have someone do the garden watering in your absence. Newly planted plants and containers can't go for long periods of time without water, especially in the hot summer months.
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Watering tips for Vegetable Gardens

  • Veggie gardens should receive about 1 inch of water when there is no rain.
  • Most veggie gardens will need to be watered during the growing season. Make sure your garden is near a water source to make irrigating easier.
  • Whenever possible, avoid wetting areas outside the plants' root zone to reduce the opportunity for weeds.
  • Avoid the overhead watering of veggie gardens. Wetting the foliage and surrounding soil promotes disease and weeds.
  • If necessary, hand water or install soaker hoses to irrigate directly to the plant's root zone.

Some suggestions for watering equipment and systems

  • Invest in a high-quality watering wand with a breaker at the end that gently showers plants but still delivers a good volume of water.
  • Using a watering wand with a local shut-off makes it easy to stop water flow in between plants or containers.
  • Use a long watering wand (24 to 36 inches long) to reduce bending and reaching.
  • Avoid using spray nozzles.  The powerful stream of water damages foliage and washes soil away.  When adjustable spray nozzles are used on mist settings, they deliver a small amount of water, requiring more time to thoroughly wet the soil.
  • Repair or replace leaky or broken hoses, sprinklers, and watering wands to avoid wasting water.
  • Buy a watering can with a large opening to make filling and mixing water-soluble fertilizers easier.
  • Install a rain gauge to know how much water rain may have already provided for your garden.

Suggestions for Watering Lawns

  • Avoid using overhead sprinklers that spray a lot of water high into the air because more water will be lost to evaporation.  Instead, use sprinklers that keep water lower to the ground and can easily be adjusted to change the delivery pattern so water can be applied directly to the area that needs it.
  • Adjust sprinklers so they don't wet sidewalks or driveways where water will just run off and be wasted.
  • Consider using spot sprinklers rather than oscillating sprinklers to water small areas, such as patches of newly seeded lawn.

Global warming is a reality for gardeners and the gardening they love to do. Now is the time to think about how we can tend to our gardens in the predicted unpredictable future of warmer, wetter weather.

By Susan Mora Loyko, Master Gardener
Author - Master Gardener