Helping plants through the heat
These 90-degree August heat waves are taxing for plants. Even when soil moisture is good, heat and disease-inducing humidity take a toll.
The threat is highest to species that aren’t heat- and drought-hardy and to trees and shrubs that have been planted in the last year or two.
When temperatures reach into the 90s, plants’ water needs go up, and plants shift energy from full-throttle growth to protecting themselves from damage. There’s nothing we can do to lower the heat, but we can mitigate the effects by making sure those plant roots have adequate moisture.
Wilting is the most obvious sign of trouble. When a plant can’t move enough moisture from roots to leaves, the leaves go limp.
The antidote is usually water. However, that’s assuming the soil is dry.
Some plants wilt from heat alone even when there’s adequate moisture in the soil. Large-leaf plants such as hydrangeas, rhubarb, and ligularia are three prime examples of that. They’ll be fine if the soil is damp.
To determine how much moisture is in the soil, you could buy a soil meter – an inexpensive probe that’s inserted a few inches into the ground.
Also effective (and free) is sticking your finger into the ground. If the soil feels damp, more water isn’t needed. If it’s dry, than a soaking that dampens the soil all around the roots and to just below them is in order.
For plants that are wilting in dry soil, the best time to water was yesterday. In other words, it’s best not to let plants get to that point.
If plants in dry soil are advancing from wilting to a yellowish-green leaf color and/or to browning around the leaf tips and edges, that’s a plant’s way of telling you it’s starting to shut down and in need of water ASAP.
The step beyond that is shedding leaves. That’s a last-ditch effort for the plant to get rid of the main way it’s losing precious moisture. Without leaves, more soil moisture is conserved for the roots.
Trees, shrubs, and perennial flowers that defoliate in summer aren’t necessarily dead, so don’t dig or yank them right away. When rain and cooler weather return, new foliage may grow – including as late as next season.
Needled evergreens are iffier. They’ll occasionally surprise by growing new needles after dropping the old ones in a heat wave. (This might not occur until next spring.) But when needled evergreens completely brown, they’re usually dead.
The two best times to water are early morning and early evening. Ideally, water directly into the ground and not over top of your plants (grass excepted).
- Read more on how to water plants in summer
- Read more on heat’s effect on plants, including ones that tolerate heat (or not)
Clean your harvest
August is a prime month for harvesting from the back-yard vegetable garden. All of those fresh, home-grown fruits, vegetables, and herbs might be at peak nutrition and free of chemicals, but that doesn’t mean you can skip standard food-handling practices.
The most important thing is thoroughly washing all produce before eating it – especially if you’re eating it raw.
Keep in mind that these crops were potentially exposed to sickness-causing bacteria and parasites from such sources as bird droppings, manures you might’ve used in the soil, and contaminants in that rain-barrel water you’ve been recycling.
This is another good reason to fence fruit and vegetable gardens or take other steps to keep animals (and their “deposits”) away from your edibles.
This includes pet cats and dogs. Kitty and Fido might like roaming the beds to sample the bounty, but while they’re there, your garden might be doubling as a porta-potty.
Three other precautions:
1.) Birds are helpful for eating bugs, and they might be nice to look at, but think twice about locating feeders in or near edible gardens. Their droppings are likely to land on your crops. Ditto for squirrel feeders.
2.) Assume rain-barrel water is non-potable. It might have contaminants from roofing materials or even bird droppings washing off the roof. Use it on ornamentals or limit it to watering into the soil below fruiting or vining plants and not over top of edible plant parts, such as lettuce leaves or root crops that are in direct contact with in the soil.
- Read more on how to safely use rain-barrel water
3.) Avoid fresh manures in the garden, and never use any manures from meat-eating animals (cats, dogs, people) even in your compost piles. Composting doesn’t always completely kill potential pathogens.
Thorough washing virtually eliminates all threats.
Cooking is a second line of defense (although it also generally lessens nutrition), and peeling is a food-safety step for produce such as apples, tomatoes, and onions.
Another good practice is one that’s been preached relentlessly for other reasons in the last year and a half – wash your hands.
Pull the crabgrass
That No. 1 grassy weed of lawns – crabgrass – is sending out its wiry green tentacles full steam now and will soon begin forming seed heads for next year’s crop.
The best way to stop crabgrass is to keep it from sprouting in the first place, which you can do by encouraging a thick stand of turfgrass (so there’s no room for crabgrass… or any other weed, for that matter) and/or by applying a crabgrass-preventer treatment in early spring.
If you’re seeing lots of crabgrass in your lawn now, you’ve probably done neither.
The battle isn’t lost, though. You do still have some options, although it’s harder to kill existing crabgrass plants than it is to stop new ones from germinating from seed.
The non-chemical, instant-result option is to remove crabgrass plants. You can do that by getting down there and hand-pulling (a screwdriver helps) or by using a long-handled weeding tool.
This is practical only if you don’t have an overwhelming quantity, of course… or are incredibly determined.
A side bonus is that the pulled crabgrass foliage makes a good compost ingredient, assuming you’ve pulled them before the plants have gone to seed.
This is more than a cosmetic improvement, by the way.
The longer you let those mat-forming tentacles spread, the more the crabgrass will shade your turfgrass and weaken it.
Even worse is if you let crabgrass produce mature seed, allowing it to drop and multiply your problem exponentially next year. Crabgrass is an excellent opportunist that will fill in any small opening, which is why growing a dense stand of turfgrass via mowing high, fertilizing regularly, and overseeding early every fall or two is such a good anti-crabgrass strategy.
This year’s crabgrass plants will die when freezing weather arrives, but its dropped seed overwinters here and sprouts the following April through June.
If you have a huge outbreak and/or are not into crabgrass-pulling, it’s possible to kill existing crabgrass with an herbicide.
Penn State turfgrass science professor Dr. Peter Landschoot says quinclorac, fenoxaprop, mesotrione, and topramezone are four effective sprays. All can be used without harming “good grass” if used according to label directions.
Landschoot posted a rundown on each of the four on Penn State Extension’s website.
Dr. Dave Gardner, a turfgrass science professor at Ohio State University, says quinclorac is particularly effective when used on fully grown crabgrass just as it’s ready to go to seed (i.e. now).
Yet another option is to ignore the crabgrass, wait for it to die and brown over winter, then apply a pre-emergent control (i.e. crabgrass preventer) next spring to head off a 2022 outbreak.
Crabgrass preventers are granular products that contain such seed-stopping chemicals as benefin, pendimethalin, or prodiamine. They’re best applied in late March to early April (a good indicator is when forsythia bushes have hit peak bloom).
Dithiopyr is an herbicide that can both prevent crabgrass seed from sprouting and kill young crabgrass plants, meaning it can be applied in May.