Native plants want to make deep roots into cool soil and you have the ability to encourage them all year long. And August is when it really counts. This is when the chickens come home to roost.

Photo: Sarah Bryant, Tree of Life Nursery © 2017

The longest days are behind us, but you can’t really notice that they are getting much shorter, since the sun is still high and the days and nights are still hot. Fall is getting closer. In just 6 or 8 weeks, we will be in the perfect time to plant natives and do major work in the garden. Until then we can safely handle warm season growers in August, while we take important precautions to keep our soil cool.

From my posts in June and July you should be well acquainted with the “pulse” method for watering where we apply 1.5”+ of water per “irrigation event” once a month. This is done by applying about .5 inches precipitation (30-40 minutes with most low volume sprinklers) on each of three days in a row, early in the morning each day. This is like three consecutive days of rain showers adding up to 1.5”+ of rain. In between these “irrigation events” you can provide “refreshing sprinkles” by wetting the foliage and moistening the ground surface with 3-5 minutes of water a couple times a week, in the early evening. Read more in June and July posts and for a thorough treatment on watering native plants see our Watering Guide. Continue these healthy summer watering practices through August.

Related to Watering
When soils are warm and wet, the conditions are ideal for root rot fungi to attack your plants’ roots. But if the roots are 8-14+” below the surface, they are growing in cool soil and are not susceptible to root rot. The problem is when you have surface roots in saturated soil, which is the result of commonly seen, too frequent and too shallow waterings, not good. In winter and spring things may appear OK as the fungal pathogens are not active. But come July and August, problems set in on plants that have become dependant on those shallow roots.

Here are the average soil temperatures in degrees Fahrenheit (approx 6” deep) for the CIMIS weather station at Irvine: October 67, December 55, March 61, June 69, July & August 75, September 71.

In my non-scientific but consistent and long term observation over several years, water mold fungi which kill native plants due to “overwatering” become most active when the soil temps reach 75° F. You have free water everywhere, and the plants are not using it, oxygen is scarce and the roots are, in a sense, drowning in warm wet ground. Not good at all.

The obvious solution is to encourage rooting into deep cool soils where the temps do not fluctuate. You can do this with monthly deep soak “irrigation events” which provide water for the roots, interspaced by periodic (twice a week or more) “refreshing sprinkles” which cool the soil surface and the leaves without actually watering the roots. See for more details. By watering infrequently, you also allow plenty of oxygen back into the rootzone. Plant roots need O2 too!

Old flower stalks and seed heads can be cut off or broken off at this time on plants like sage, sunflower, and penstemon. You can leave most buckwheat bloom for now to fade from white to tawny to brown. They are attractive, they are shading the plant and their seed is developing. If you want to sow seed you have trimmed off your plants, just stomp on the severed seed heads and make a “mulch” out of them. Some will probably germinate next spring. Do not prune any plant severely; you should save that task, as needed, for a cooler season. No major pruning of woody shrubs at this time.

Fast growing heat loving plants like desert lavender, desert mallow, verbena, lobelia, and goldenbush and for that matter any other plant that has enjoyed the warm weather and grown out of bounds, (lemonade berry, baccharis, sumac) can be pruned back to give it a better shape going into fall. Selectively trim the branch tips. Vary the lengths of the pruned pieces. Try to avoid the sheared look, unless that is your stated pruning style for that plant.

You should have already dealt with most of your summer weeds, but keep up on removal of spotted spurge, oxalis, telegraph weed and other heat loving uninvited guests.

Mulching/Top dress
If you have a 2” layer of organic mulch or top dress, it might be showing its age, or the season, with accumulated salts, compaction and an overall “tired” look. Feel free to get out there with your 3-prong scratch cultivator and scratch scratch scratch to open up the matted mulch, let some new air in, allow better water penetration, and give the earthworms and other soil biota a new lease on life. On the same day, late in the afternoon, run the sprinklers or water the whole place by hand, just enough to soak through the mulch. Your garden will be fresher and it will even smell like a summer thunderstorm just came through.

Delay most feeding until cooler weather. Watch future posts for details. If you have any potted plants, and they are actively growing, you can use a water soluble all-purpose plant food like Miracle Gro. this is especially good on desert plants, cacti and succulents and other warm season growers.

Troubleshooting – Varmints, Pests and Diseases
We covered summertime pests in the July post. Keep an eye on Argentine ants, as they bring aphid and scale onto your plants. In moist shady areas, an infestation of brown garden snail is always a problem.

We should all be aware of two serious pests that threaten our large trees, native and otherwise:

Golden Spotted Oak Borer (GSOB):

Polyphagous Shot Hole Borer (PSHB)

Annual Wildflowers
As in July, allow seed heads from last spring’s flowers to drop seed for next year. You should do no new seed sowing at this time. Fall will be here soon enough.

Adding New Plants
This is a great time to plant heat loving desert species and other warm season plants, and certain shade plants. For most natives, especially in full sun, first take a look at the spot you want to plant, then take a look at your calendar. Now imagine cooler soils, shorter days, rains just around the corner, and uninterrupted progress for your plant through the cool season. Aha! your eye must be focused on the calendar page for October. It’s closer than you think.

The aromatic foliage, dried flower/seed heads, summer bloomers that announce hot days, hummingbirds darting here and there from dawn til dusk, and pollinating insects that visit flowers in hourly “shifts” based on their species, form the basis for your summer experience in the natural garden. My favorite times are early morning and late evening… including after dark… when the garden takes on new meaning. You can set some quartzite or other white rocks in key spots along the path to serve as moonlit guides for your pleasure while out exploring.

From the Garden,

Mike Evans

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