Gardening during a heat wave

The Catskill region and Hudson Valley have already experienced their first major heat wave as temperatures climbed into the low 90s and stayed there for several days last week.

Lawns, already suffering from drought stress, may not turn green again until fall if the heat continues much longer. Best to put away the lawnmower for now since mowing stresses grasses and will hasten dormancy if the grass is not already brown.

This is a good time to evaluate your lawn, since many common lawn weeds are much more tolerant of heat than turfgrass. Clover, plantain, chickweed, crabgrass, wild strawberries, wild thyme, violets and other broad-leafed weeds remain green as grasses go dormant. Crabgrass is not a broad-leafed weed, but it is much more tolerant of heat and drought than more desirable grasses.

This is not a good time to apply any herbicides to try to get rid of any of the weeds listed above. Most lawn herbicides only work on actively growing weeds and few plants are actively growing now. Some herbicides can “volatize” when temperatures are over 85 and the invisible fumes that are produced can harm plants as much as 50 feet or more away.

Tomato plants in particular are sensitive to herbicide “drift.” Wild strawberries and creeping thyme indicate that the soil is acidic and may need an application of lime. Wait until rainfall returns before adding any lime or other chemicals to your lawn.

This is a good time to divide some spring flowering perennials such as bleeding hearts, early iris, lungwort, astilbe, creeping phlox, tiarella and columbine. Wait until September to divide peonies, though. Water the plants thoroughly the day before you plan to dig them up and either wait for a cooler, cloudy day, or do it in early evening to reduce stress. Cut the tops back by two-thirds before digging them up. Keep the newly divided plants well-watered.

Iris actually need to be divided every few years since they often are attacked by borers that destroy the central part of the clump. Replant only the outer portions after carefully examining them for evidence of the ugly grubs.

I have come to really enjoy seeing several roadside “weeds” that I am considering deliberately planting near my gardens, since they are seemingly maintenance free. Some would consider these as “invasive” but that trait is not always a bad thing. This spring I noticed that a “volunteer” specimen of “Dames Rocket” (Hesperis matronlalis) was coming up in the gravel just in front of my perennial garden. Since I could use some shade to protect the woodland herbs I am growing there, I decided to just let it grow.

Right now it is finishing up a solid three-week bloom period, so I cut it back to about one foot high. The pretty pink/purple flowers in long spikes, sometimes fading to light pink or white, make excellent cut flowers. Next spring I may pinch it back when it first comes up, give it some fertilizer and see just how impressive it can be with a little TLC.

I have also noted a roadside plant called “hemlock parsley” (Conioselineum chinense) that closely resembles poison hemlock. I may dig some of these up and try them, also in front of the woodland perennials to provide shade. It features delicate, almost lacy foliage topped by a large umbel of white flowers. I suspect that, like Dames Rocket, it will tolerate the hard-packed gravel.

Finally, the oxeye daisy, (Chrysanthemum leucanthemum) actually is a “weed” in my vegetable garden, but only because it out-competes my vegetables and is a perennial. The pretty white flowers also make great, long lasting cut flowers. I wonder how this plant will respond to fertilizer and water?

All of these wildflowers, or “weeds,” if you prefer, are intended to provide some shade early in the season and they all can be cut back hard after bloom. I can think of some other cultivated garden plants or herbs that can also be very invasive such as Oriental poppies, any type of mint, feverfew (an annual that comes back each year), lemon balm, bishops weed, ajuga and even myrtle.

Several years ago I wrote about a disease called “rose rosette virus” that seemed to be selectively killing off the very invasive “multiflora” rose, which has spread rapidly in recent years. I welcomed this introduction because most of the time, I really dislike multiflora rose. The nasty prickles seem to jump at me, tearing my skin every time I go anywhere near it.

Well, it seems that the rose has developed a tolerance for the virus and is surviving and spreading once more. As Michael Creighton wrote in “Jurassic Park,” “life finds a way.”

Reach Bob Beyfuss at rlb14@cornell.edu.

Johnson Newspapers 7.1

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