Watering During a Heatwave

By Portland Nursery

Hot weather will likely be arriving before long and we have some important tips we wanted to share with you so you’re ready.

Tips for Watering

Watering deeply BEFORE high temperatures arrive is ideal. For most plants, watering in the morning or evening is best. Getting water on leaves will not cause burning. It can abet fungal diseases in some plants (roses, squashes), so watering most plants in the morning is ideal.

Adding a layer of mulch to soil surfaces helps to maintain moisture in the soil.

Moving some plants into shady areas or setting up shade cloth for the duration of the heatwave can help.

New Plantings

Newly installed plants are among the highest priorities for watering during a heatwave. These plants have not rooted into the ground completely and are at a greater risk of drying out during times of excessive heat. Water new plantings deeply, using soaker hoses, drip systems or sprinklers.

Deep watering entails watering at a slow pace for long enough that the water soaks deep into the soil, where the roots are. Often this means watering for 30-60 minutes at a time, two to three times each week, until plants are established. When temperatures normalize, continue with deep watering, but back off to one to two times each week.

Tree bags are fine to be used for newly planted trees, but only for short periods of time. They should be removed between waterings to avoid causing rot at the base of the tree’s trunk. Tree bags are not effective for watering established trees because the roots of a mature tree extend far beyond the trunk.

Shading newly planted areas with umbrellas or shade cloth can really help to reduce heat stress.


Plants in containers dry out faster than plants that are growing in the ground, and during a heatwave they may need watering more than once a day.

When you know an extreme hot spell is coming, it can help to move smaller containers into shaded areas just for the duration of the hot weather. Hanging baskets can be helped by placing them on the ground. 

Hanging baskets and containers of annuals lose a lot of their nutrients when they’re watered this often, so it’s a good idea to fertilize after the heatwave is over.

Established Plantings

Even the most established plants in our gardens appreciate a deep soaking a few times during summer, and indeed fortifying them with a long slow watering before a heatwave is a good idea. It’s important to apply water to the whole root zone, which reaches at least to the dripline of the plant.

Use a soaker hose or sprinkler for 30-60 minutes at a time. During normal summer temperatures, this type of watering can happen every two to three weeks. In times of extreme heat, one to two times each week may be necessary.

Know your plants, though! Some plants prefer almost zero water during summer (manzanita, Ceanothus, madrone and cistus) and others wilt even when they have ample water (hydrangea, rhododendron). So adjust watering accordingly.

Veggies & Fruits

Vegetables and fruits that are developing fruit during a heat spell need regular watering to ensure good production. Vegetables typically require daily watering during summer weather, but may need a second watering when temperatures are extremely high.

Lettuces and other leafy crops can be kept from bolting (going to seed) by misting or watering their leaves in the afternoon.

Tomatoes prefer even and consistent watering to help curb Blossom End Rot, so try to keep them evenly moist. Adding lime to soil when planting, and spraying with Fertilome Yield Booster can help to correct calcium deficiency and prevent Blossom End Rot. Sprays should only be applied when temperatures have dropped below 85 degrees.

Helpful Products

Soaker hoses are a great way to deliver water at a slow pace, allowing it to sink deep into the soil where roots are located. It can take time for water to seep in, so soaker hoses should be turned on for at least 30 minutes at a time.

They work best on even ground, should be no longer than 100 feet to be effective and should be placed in such a way that water reaches the entire root zone. Hoses operate well when water pressure is lower, so don’t crank the faucet up too high.

Adding shade cloth to help keep the air temperature down and reduce transpiration is a great idea. It’s often just needed during the duration of the heat spell and can be removed when temperatures normalize. It’s very helpful to use when plants that prefer shade are accidentally planted in sunny sites.

The shade cloth that we carry at Portland Nursery will block 70 percent of sunlight. We offer several colors, and they are all equally effective–the color choice is completely aesthetic.

If you want to give plants a bit of TLC after a heatwave passes, applying Maxicrop Liquid Seaweed to the leaves is a good idea. It provides a light blend of nutrients and trace minerals that will provide a bit of nutrition while plants recover.

Watering During a Heatwave

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