It’s still too hot to plant or transplant in August but there are several gardening chores that can and should be done this month to keep our trees, plants and soil healthy.
▪ Soil solarization: It only takes 4 to 6 weeks of solarizing or baking the soil during the hot summer months to kill weed seeds, disease pathogens and nematodes in the top 12 to 18 inches of soil. Daytime temperatures in our area will remain high enough until mid-September to completely sterilize the soil, giving us just enough time to prepare for fall planting.
Soil solarization also increases the numbers of beneficial micro-organisms and earthworms (they wiggle off to cooler depths during solarization), creating much healthier growing conditions.
I’ve written several columns giving instructions for soil solarization, and directions for this simple, very effective process can also be found on the UCDavis website, http://ipm.ucanr.edu/PMG/PESTNOTES/pn74145.html.
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Soil solarization can also kill Bermuda grass rhizomes, seeds and stolons that have been previously treated and weakened by several applications of glyphosate (i.e., Roundup). During the late summer and early fall months, the underground rhizomes and stolons of Bermuda grass grow more rapidly and glyphosate applications are most effective.
▪ Deep irrigation of landscape trees: Although rainfall amounts were above normal this last season, we’re still seeing the effects of four years of severe drought on mature landscape trees. Continuing tip and branch dieback this late summer are signs that tree roots are not receiving enough water and are drought-stressed.
Deep-irrigate your landscape trees by placing drip emitters, soaker hoses, small oscillating sprinklers or bubbler attachments on a hose at the edge of the leaf canopy where “feeder” roots draw up the most water. Proper placement of irrigation sources is key to providing sufficient water.
Allow water to slowly soak the soil over a period of several hours to a depth of at least 1 foot. Check soil moisture levels weekly and deep irrigate again when the top 3 to 4 inches of soil is dry – that may be every four to five days when temperatures are above 90 degrees.
▪ Resume fertilization: When daytime temperatures are regularly above 95 degrees, plants stop growing; they don’t set flowers and they don’t push out new green growth. Fertilizing heat-stressed plants only stresses them more. We stop fertilizing in July and resume feeding our plants in mid- to late August when hot days are shorter and cooler nights are longer, allowing plants to better recover from high temperatures.
Feed plants at half the recommended rate in late August with a low number, lower nitrogen (less than 10 percent) fertilizer, like a 4-6-2 formulation (the percentage of nitrogen is always the first number on the label). Bone meal, which is high in phosphorus, the second number, encourages flower production and can be used on tomatoes, squash, beans and other summer vegetables that dropped flowers during the July hot spells. A few tablespoons per plant applied every two to three weeks should be enough to help set a new fall crop.
Compost can also be used during hot months as a side dressing; scratch a half cupful into the soil alongside the stems every two weeks. Fertilizing with low- or no-nitrogen compost or bone meal will give your plants a slower, gentler restart in late summer when temperatures are still high.
Send Elinor Teague plant questions at firstname.lastname@example.org or email@example.com (“plants” in the subject line).