by Susan Harris
This is NOT a normal summer, Gene Sumi told shoppers during Homestead’s Myrtle Festival – in the middle of the longest hot spell in anyone’s memory. It all started in April, when it’s not supposed to be in the 90s, but was. Then for weeks now it’s been consistently above 85 degrees, which Gene says is a common cause of summer stress. He quoted former AHS president Dr. Marc Cathey, who famously promoted new and improved heat zones that indicate which plants suffer when the temperatures are consistently high. While most garden plants do survive prolonged heat, many fail to thrive, and gardeners need to understand this. Dr. Cathey worked to explain why some plants do well in Pennsylvania, but not here in Maryland. (Sometimes it’s not the cold, it’s the heat!)
The Signs of Stress
Leaves turning yellow, then dropping are the key symptoms of summer heat stress, and watering more may not solve the problem (though DO try that first if your plants haven’t been watered adequately). Actually there IS no cure. Just keep on watering sufficiently (not maniacally), and the good news is that most plants will look good again when the temperatures go below 85 – soon, we hope.
Watering, Conserving Water
Watering deeply is the most important lesson here – even for shallow-rooted plants. Deep watering makes the roots go deeper, thus making the plant more drought-tolerant. To prevent overwatering, don’t water again until the soil under the mulch is dry. Dry mulch is fine – it trains the plants to wick water from deep in the soil - so Gene recommends we don’t keep the mulch moist at all times but rather, let it dry out between waterings.
More tips: Do NOT water a little bit every day. Don’t be afraid of wilt – “It’s not the Grim Reaper coming.” Also, soaker hoses are popular, and a “great tool.”
For trees, Gene likes the Gator Bags and Treegators that are filled with 15-20 gallons each and placed around trees, where they deliver the water slowly over eight hours. (Many users double up with two, providing a total of 40 gallons.) Landscape contractors report that these tree-watering devices are “saving graces” for newly planted trees.
Lawns: The University of Maryland recommends giving lawns one inch of water per week, and Gene says the best way to make sure we’re providing one inch – no more, no less – is by placing containers around the garden, then watching to see how long it takes for the sprinkler to provide one inch.
Veg Gardens: Gene recommends one inch of Leafgro compost as a mulch (or the leafmold he used to use before Leafgro was on the market). Both hee and garden guru Mike McGrath prefer compost on vegetable gardens over raw bark mulches because compost has already broken down. It contains nutrients, helps retain soil moisture, prevents splashing up of fungal spores from the surface of the soil, and will not rob the soil of valuable nitrogen.
We’re used to seeing insects and fungi attack stressed, weak, and vulnerable plants but this summer, even the healthy ones are suffering. The best way to prevent summer stress is the simple use of good gardening practices - watering adequately, using mulch, and checking on the plants regularly. Gene laments the many customers reporting “large-scale plant devastation” and urges us to avoid this fate. (As Gene told me in a follow-up email, “I feel like I’m playing a doctor on TV. I’m telling customers that no, the spray will not make their plant look as good as new and no, I cannot guarantee that the plant will survive this pest attack.” It’s tough doing garden triage!)
If you DO apply a pesticide, make sure the plants are well hydrated first. (Actually, labels warn that using the product on drought-stressed plants can make problems worse, but those labels don’t always get read.) And sorry to say, organic products don’t work 100 percent of the time – more like 70-90% of the time – but he still recommends we use them, rather than the synthetics.
The best way to deal with weeds in the lawn is to avoid them in the first place – by having a thick lawn. That means overseeding and making sure they get the nitrogen it needs.
For most plants, don’t apply fertilizer now but wait until the fall. Gene says plants can’t take in the fertilizer without active uptake by the roots, which only happens when there are green leaves on the plant. Feed perennials and deciduous trees and shrubs in the early fall. Feed evergreens in November.
Summer feeding is recommended only for zoysia turf, annuals, vegetables, and roses. (Annuals “have a fast life but they die young”.) For roses, Gene recommends removing dead flowers and feeding the plant after each bloom cycle.
Do NOT prune spring-flowering shrubs like lilac, azaleas, and rhododendrons now – the best time to prune them was soon after their blooms faded. That’s because just about all spring-blooming trees and shrubs produce the next spring’s blooms in August-September, and if we prune after mid-July we’ll probably be cutting off next spring’s blooms. July 15th is a conservative drop-dead date, after which we shouldn’t do any serious pruning (removing dead flowers is okay).
Spring and early-summer-blooming hydrangeas pose a unique problem for pruning because we’re supposed to prune after they bloom but they have an “irritating habit” of blooming til mid-summer and by then we’re afraid of removing next year’s buds. Gardeners want to enjoy those long-lasting blooms, but don’t know what to do. Gene says he tells customers to “Enjoy another two weeks of summer blooming and don’t prune them at all. Or prune them before the end of July and sacrifice those extra two weeks of blooming. Or lastly, prune them late and accept that you will have fewer blooms next spring.” Take your pick of the choices.
Another possible solution is to plant ‘Endless Summer’ types that allow us to have our cake and eat it too – because they bloom both on last year’s buds AND on the next year’s buds. So prune ‘Endless Summers’ now if you want to prune – but you don’t have to.
Deadhead roses as their blooms die – except for Knockouts. They don’t need it because they’re “self-cleaners,” meaning their dead flowers drop off. Nice of them to do that!
Don’t prune evergreens in the fall. They make most of their food in the winter when maximum sunshine reaches them – because deciduous trees have lost their leaves.
More Summertime Tips
- Replenish your mulch all year long, to maintain a two-inch layer. And no, there’s no need to pull it back in spring.
- For more on this subject from Gene – his hand-out on Summer Garden Maintenance.