August in the Ornamental Garden

August in the Ornamental Garden

  • By Cathy Caldwell
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  • August 2020-Vol.6 No.8
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  • 0 Comments

The record-breaking heat of July, coupled with minimal rain, has about done in my garden, not to mention its gardener.  My ornamentals are either sunburned, freckled with holes from chewing insects, or appear to be in some sort of permanent swoon.  Will August offer some relief?   Historically, the first half of August has been much like July. Unfortunately, weather extremes have become the new norm, so we’d best prepare for any and all of them.

Are my plants really sunburned?  Well, extreme heat can cause plenty of damage.  To read more about this and to look at photos of a variety of plants impacted by heat stress and drought, go to “Scorch, Sunburn and Heat Stress,” Mo.Botanical Garden.  What might appear to be a disease or pest could actually be the result of extreme heat and drought.

As you plan your August tasks, be sure to start with Monthly Gardening Tips – August, Gardening Resources, PMG.

Watering has probably been your primary activity lately, and August may be no different. Rationing water among my plants is a daily dilemma, as it is for many of us whose water is supplied by a well.  My question of the morning is — which plants look worst?  Actually, newly-planted shrubs and trees must come first, of course, but how do I decide between the beds near my front door, the borders in the back, and my cutting garden? Or between my edibles and my ornamentals?  Setting a schedule may help; try to focus on one area per day.  But containers are another matter; they need water every day. If the hot, dry weather continues into August, you may need to water established plants.  If so, soak shrubs with enough water to moisten the soil to a depth of 8-10 inches, if possible.

Arranging the soaker hose. Photo: Cathy Caldwell

In past summers, watering was rarely necesssary, and mostly only for the recently-planted investments, like shrubs and trees.  But now I have a new investment — soaker hoses. They not only use less water, they put it right where it’s needed. However, trying to arrange them effectively in my curvy ornamental beds has been a learning experience.  And I’ve discovered that you can’t just cover the hoses with mulch and forget them.  Periodically, the output of soaker hoses needs to be checked to make sure they haven’t gotten plugged up by calcium deposits, small grains of sand, or other debris.   Plus, some well water contains a bacteria that feeds on the iron in the water.  This bacterial iron can, over time, create a slime that severely restricts the flow of soaker hoses.  Even if you have installed a water softener, it’s probably only processing your indoor water.  Read more about this problem in “Silence of the Soaker Hoses,” Mich.St.Extension.

Here’s the rest of the To-Do List:

  • Stay on top of routine maintenance chores such as weeding and watering. Did I mention watering?
  • Add more mulch, especially around plants that look stressed.
  • Monitor plants for diseases and pests.

Spider Mite damage on holly (left); normal holly on right. Clemson University – USDA Cooperative Extension Slide Series , Bugwood.org. CC BY 3.0

    • Be on the lookout for lace bugs on rhododendrons and azaleas, which can also be bothered by spider mites.   I’ve been trying to figure out if it was one of these insects that just recently attacked the newest leaves on my rhododendrons. However, lace bugs and mites cause similar damage — tiny spots or “stippling” —  so it’s difficult to be certain which pest you’re dealing with.  For guidance on how to distinguish between the damage caused by these two, check here: Lace Bugs/Va.Coop.Ext.. For more detail about common pests of rhododendrons, see  NC State Ext. Pests of Rhododendron.

 

Adult two-spotted spider mites. Photo: Frank Peairs, Colo.St.Univ. Bugwood.org, CC BY 3.0

    • I recently learned that the population of two-spotted spider mites — a very common type which attacks a wide range of plants — increases as temperatures rise, so keep an eye out for these tiny mites if our hot weather continues.  Here’s how to scout for two-spotted spider mites in your garden:  “Scout for Two-Spotted Spider Mites,” N.C.State Entomology.  But do NOT use pesticides when you find spider mites because the use of foliar insecticides in hot, dry weather can actually cause or increase spider mite outbreaks by killing the beneficial insects that feed on the mites. Be aware that fungicides can eliminate another natural enemy — a fungus that attacks spider mites following short periods of cool, damp weather.  Your best defense is heavy rain (yes, please) or a strong spray from a hose, which can knock spider mites off a plant. Try the water spray method for several days in a row.  Read more here:  “Mites Found on Flowers and Foliage,” NC State Ext.Spider Mites in Home Gardens/Univ.of Minn.Ext. and “Twospotted Spider Mites on Landscape Plants,” NC State Ext.
    • Azalea Lace Bugs. Photo: Jim Baker, North Carolina State Univ., Bugwood.org, CC BY NC 3.0

      Another pest to watch for is the azalea lace bug; its population can get quite high in August and September. If only a few lace bugs and little or no damage is observed, use the same “strong stream of water” technique that’s recommended for spider mites.  Repeated applications of insecticidal soaps or horticultural oils are also effective against large infestations, but early spring is the best time to control lace bugs, so make a note to monitor any infested plants next spring.

  • Deadhead annuals and perennials. Deadheading not only improves the appearance of plants but also encourages some species such as coneflower, garden phlox, and salvia to continue blooming. Keep in mind that some dried flower heads on plants such as tall sedum, globe thistle, astilbe, and coneflower can look attractive throughout fall and winter, so you might want to leave them in place.
  • Tidy up daylilies by removing yellowed or dried flower stalks all the way to the ground and all browned or yellowed foliage. Cutting the spent flower stalks back also triggers reblooming daylilies to produce more blossoms.
  • Trim away yellowed or tattered leaves as well as any that have been heavily damaged by insects.
  • Cut back leggy or spent annuals and give them some fertilizer to revitalize them. Within about two weeks, the annuals should produce fresh, new foliage and another round of blooms.

Fall Webworms.  I’ve been seeing a lot of webworm nests lately. The webs are unsightly, but generally do NOT pose a serious threat to the health of the affected tree or shrub due to their timing — late in the season.  Apparently if webworms spun their webs earlier in the season or were able to consume a larger portion of a tree’s leaves, they would indeed be a threat.  But the leaves consumed at this time of year have already made their contribution and will be dropping off soon anyway. Plus, webworms do not eat the buds of future leaves, so the growth on affected branches will look perfectly normal next spring.

Fall webworm nest. Photo: Cathy Caldwell

It’s usually NOT necessary to do anything about webworms.  But if you decide to prune off the webs, dispose of them in a way that will prevent the webworms from reproducing — such as garbage bags or burning. Pesticides are not recommended;  the webs are more or less impervious and sprays are repelled off. It would be necessary to tear a hole in the webbing to access the inside. If you are close enough for this, pruning is a much better option.  If you want to be educated and entertained at the same time, you’ll want to read an article published by Michigan State Extension, wherein the author, Gretchen Voyle, explains the “10-year-old boy” method for dealing with webworms:

“If fall webworms are on a small tree and you choose to remove it, the easiest way could be called “10-year- old boy biological control.” Push a stick into the webbing and pull everything and everybody out of the tree and into a bucket of soapy water to soak for the day. Or the webby mass can be burned or buried.

–The rise and fall of the fall webworm,” Mich.St.Extension

To learn even more about webworms, check out this article Mo.Botanical Garden/fall webworm.

Blue mist flower (Conoclinium coelestinum), a native that usually starts blooming in August. Photo: Chris Evans, Univ. of Illinois, Bugwood.org, CC BY-NC 3.0

Take a break now and then to enjoy your garden.  Some plants seem to persevere through extreme conditions, so focus on them.  What’s doing well in your garden?  Do you need to replace some plants with more drought-tolerant ones? As summer wanes, take notes about which perennials will need dividing later (though iris can be divided now).  And think ahead to the pleasures of the autumn garden.

 

SOURCES:

Spider Mites on Ornamentals/Purdue Extension

Control of Lace Bugs on Ornamental Plants, Univ. Ga.Ext

Morning Glory ‘Kniola’s Purple Black’
Photo: Cathy Caldwell

Featured photo:  Kniola’s Purple-Black Morning Glory, an heirloom discovered by Mr. Kniola at an abandoned farm in Indiana. I obtained seed from J.L. Hudson, Seedsman many years ago, but apparently he passed it on to Roberta Bailey, a seed saver.  I have been able to find only one online source for this seed, Hudson Valley Seed/Kniola’s Purple Morning Glory, which at present lists it as out-of-stock.

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