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Ann Wright: A scorching, smoky start to September

Ann Wright


As gardeners, we learn something from every growing season. This year has been another new journey with my garden, and coming out of recent record-breaking heat has provided information for next year. In wandering around my garden one cooling evening after a run of triple digit heat and grueling sun, I noticed several very sad looking plants, including some scorched needles on conifers and dead-looking leaves on some shrubs.

Living in a Mediterranean climate as we do, it is natural to expect hot, dry summers. But, really? The thermometer reached 110 at our house in Penn Valley, and some of the plants show every degree of heat stress, sun scald and possibly near-death. After wringing my hands a little, it seemed a good time to make written or mental notes about the overall condition of the garden and the things that must be done with the next staggering heat wave, and I trust there will be others.

We know that plants are injured when temperatures heat up the root zone, or the canopy of trees. The plant tissues become dehydrated which kills plant cells. Couple prolonged heat with lack of water and moisture, the result may be injury or death to the plant. Injury to roots can occur when soil temperature rises above 105F; plants in containers and unshaded raised beds are particularly at risk for root injury from heat. Landscape plants are less likely to incur root stress as the soil acts as insulation.

One of the steps that will be taken with the next heat wave is to ensure the plants are adequately watered. With water restrictions, it may be necessary to prioritize which plants will get the abundance of water. First, for newly planted trees, shrubs and ornamentals, take care that the tender roots have enough water to sustain days of heat. Water when the top 3 or 4 inches of soil is dry, and water until the soil is moist to a depth of 8 to 10 inches. Note to myself: Check soil moisture using the screwdriver or rebar method: insert the chosen tool to a depth of at least a foot, and see if there is moist soil detected. Or, dig a small area adjacent to the plant to see if the surrounding soil is damp.

Second, two words: shade cloth! For young plants, or any plants very vulnerable to heat stress and sunburn, add some shade – by shade cloth, umbrella or whatever you have to shield the plants from the scorching sun. And avoid planting species that are not well adapted to our area. For example, the dwarf blue spruce I planted in a backyard rock garden will be better suited to a location with more shade – and, if the poor thing survives it will be transplanted this fall. Consider local California native plants that are suited to this climate.

Another tip is to make sure there is ample mulch around new plants. Mulching is simply the process of covering the soil around plants with organic material, such as straw, wood chips or bark. Mulching helps protect roots from high temperatures, and will help reduce loss of soil moisture. Mulches can also help reduce soil compaction and erosion. (One essential rule to using mulch is to pull mulch material away from the base of the tree or stem of the plant. Piling mulch against the base of tree trunks or smaller plants causes moisture to build up which may contribute to root and crown rot.)

Determining whether a plant has heat stress, or us under-watered will help make decisions about what to do. Some indications that a plant is under watered include, leaves that are limp and dull. Brown tips may form, followed by leaf drop. If the plant continues to experience underwatering, the leaves won’t grow back. If the plant seems to be underwatered, don’t flood it. Just apply enough water to moisten the soil to about 2 or 3 inches. Then, add water based on the type and location of the plant.

In addition to staggering heat, we have also had hazardous and unhealthy smoky air — sometimes it has been difficult to tell if there are clouds or just smoky haze. Pausing to consider the effect of smoke on garden plants and produce, two things stand out: First, if there is smoke in the air it may be a good idea to stay inside, and secondly, wash the ash and soot off the produce before bringing it into the house and wash again before preparing it.

Due to the excessive heat and smoke, our workshop scheduled for September 10 – “Compost: Good for You, Your Plants and the Earth” was postponed. Watch the Master Gardener of Nevada County website (https://ncmg.ucanr.org/ ) for details of when the workshop will be rescheduled, as well as information about other workshops and events.

Ann Wright is a Nevada County Master Gardener

Dwarf Blue Spruce with scorched needles.
Photo by Ann Wright
Scorched nordman fir.
Photo by Ann Wright
Scorched leaves of Beauty Bush (Kolkwitzia).
Photo by Ann Wright


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