Recent hot temps and high humidity can bring stress to plants. We field many calls and emails during summer from people seeing more bugs and fungal issues so we asked our expert staff to answer your top 10 summer questions to maintaining healthy plants. Our approach is to do what is best overall for the ecosystem. We recommend using natural products and practices whenever possible.
Q: Why are the leaves on my plant turning yellow?
A: This is typically from overwatering or underwatering. Be diligent in testing the soil under the mulch. The soil should be dry 1”-2” under the surface before watering. If you are unsure, using a moisture meter can help you determine when to water your plants. Eric, in Trees & Shrubs, says newly planted trees and shrubs typically need 1” of water per week. To water, place a slow trickling hose at the tree base for 20 minutes. Hand watering is more reliable than a sprinkler for new plants. Water the roots of perennials and annuals, not the leaves. Water in the morning to allow for any excess to evaporate before nightfall. Annuals, vegetable plants, and plants in containers may require more water on hot summer days so check regularly.
Q: How often do I water my new plants?
A: Test the soil for dryness daily the first week, every other day the second week, and every third day the third week.
Q: My Catmint and Salvia have bloomed and now look tall and floppy. What do I do?
A: Perennials need deadheading in the summer. Once you remove the spent flowers it diverts its energy into root development or, for some plants, a second bloom. As a general rule, using sharp pruning shears, cut off the bloom and stem down to the next new bud or flower. If there isn’t a flower, then cut to the first lateral branch to avoid leaving stems or stubs sticking up. Daylily stems can be pulled out easily once the flowers are spent and the stalks turn brown.
Q: Do I prune my roses now?
A: Sometimes roses need pruning to help revitalize and reshape the rose plant. Late winter to early spring is when you remove all canes that are dead, diseased or damaged, and prune back to live growth. Re-blooming roses can be deadheaded in summer as they begin to fade to encourage the rose to rebloom. Cut off the spent blooms about 1/4″ above the first 5-leaf junction at a slight angle. It takes around 6 weeks for a rose to form new buds and to bloom again. One-time blooming roses, such as Hybrid Tea, Grandiflora and Floribunda roses, have buds that form only on wood from the previous year’s growth and should not be pruned back drastically or you’ll sacrifice flowers. Leave the last bloom on your roses to form rose hips on the plant for winter interest. If you have been regularly fertilizing your roses, it’s time to stop.
Q: How do I keep the Japanese Beetles from eating my plants?
A: Cristin, in our Tree & Shrub Dept. says the best solution is to knock them into a bucket of soapy water. If using a Japanese Beetle trap, she recommends placing the trap in a remote corner of the yard far away from the plants the beetles like to eat.
Q: What is eating the Milkweed (Asclepias) I bought to attract butterflies?
A: Kyle, our Perennial Manager, says if you want to see butterflies in your garden, you’ll have holes in some leaves. Along with hungry Monarch caterpillars, you may also see Milkweed Beetles. Beetle damage is usually not serious and doesn’t warrant treatment.
Q: What is the big, green worm with red horns on my tomato plant?
A: These are Hornworms. Linda, one of our Veggie gurus in Annuals, says they can eat their weight three times over and defoliate a tomato in a day. To stop them from eating your tomato plants, pick them off and put them in soapy water.
Q: Any idea what insect bores into branches and lays eggs on the leaves?
A: Boring Wasps tend to be solitary opportunists, typically preying on plants that are stressed. Cristin suggests trying to kill the wasp by opening a paper clip and pushing it up through the hole in the damaged stem. Put on gloves to squish any egg masses found on leaves, and prune out the affected stem after you try and kill the wasp.
Q: What is the orange, hairy-looking growth on my Serviceberry?
A: Cedar Quince Rust is an orange fungus that usually shows up this time of year on Hawthorn fruit. After a wet May, we are seeing it on Serviceberry. Cristin adds “It does ruin the fruit for this year, but it won’t do much damage to the plant itself and it is too late for treatment.”
Q: What causes brown circles surrounded by a yellow halo on my plant’s leaves?
A: A fungus in the soil that bounces up on foliage when it rains is Early Blight. Linda says the best way to prevent it is to put down a bio-degradable craft paper, cardboard, landscape fabric, or mulch to separate the soil from the foliage. Control blight on the plant by taking those leaves off before covering the soil. Rotating crops is also effective since Early Blight is particular to tomatoes.
BONUS Q: My peonies have bloomed and now have a white, powdery mildew on the leaves. What do I do?
A: Monarda, peonies, phlox, and lilacs are some of the most susceptible. If much of the plant is covered with this white, powdery mildew, you can cut back monarda, peonies, and phlox by 1/3 to 1/2. For lilacs, see if any branches need to be removed to improve air circulation. The mildew spores can overwinter so do not put them in your compost bin or leave them lying on the ground. Linda applies a solution of water and milk, 10 (water) to 1 (milk), for powdery mildew on cucumbers and squash. It doesn’t stop it but controls the mildew enough to get the fruit off of the plant.
Don’t see your question here?
We’re happy to answer any questions you might have. You can call us in Aurora at 630-820-8088, in Naperville at 630-355-4000 or email us at firstname.lastname@example.org with 1-2 small sized photos with a description of the problem.
Need us to help diagnose what’s wrong?
If you’re not sure what’s going on with your plant, you can always bring in a sample to our Tree and Shrub department at either location. Put your sample in a transparent, sealed, plastic bag and we can help diagnose the problem. You can also send 1-2 small-sized photos to email@example.com with a description of the problem.