Garden Detective: Helping hydrangeas

Not fans of full sun, hydrangeas perform best

Not fans of full sun, hydrangeas perform best in shade. (Credit: Michael Galvin)

DEAR JESSICA: I hope you can help me. I have four hydrangea plants in a garden facing due east and four in a garden facing due west. They get water every night from the automatic sprinklers. The east-facing plants get sun until noon, and the west-facing ones get sun from noon until the sun sets. Last year all the leaves turned black and shriveled up. Also, some of the leaves always seem to get dry and curl, and they also seem to have holes chewed in them. Can you tell me what might be going on or what I might be doing wrong? --Maureen Hesse, West Babylon

DEAR MAUREEN: There are a few different things going on with your plants. Both viral and fungal diseases can turn hydrangea leaves black. It's very possible your plants fell victim to a fungus because of your watering practices. Leaves should be kept dry to keep mold and mildew from taking hold. Your automatic sprinklers, which really should be relied upon only for the lawn, are wetting the whole plant. This is compounded by the timing of your watering: Sprinkler systems should be set to run only in the early morning. Nighttime watering leaves plants (including grass) wet for too long before the sun can dry them, encouraging the growth of mold and mildew. Too much humidity, including that retained between plant stems, is a perfect breeding ground for both viruses and fungi.

Another factor could be too much sunlight. Hydrangeas perform best in shade, and full sun could be causing their leaves to dry and curl. That wouldn't explain the discoloration of the leaves, unless they turned dark brown (as most dry leaves do) and not actually black.

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The third consideration is that your plants were attacked by aphids. This is absolutely possible but the least likely, because your eight plants are located in two separate garden areas. Aphids are tiny, pinhead-sized insects that attach themselves to the undersides of leaves, where they go largely unnoticed. They sink their piercing, sucking mouthparts into the leaves and suck out the sap. Then they excrete a sticky substance called honeydew, upon which black, sooty mold grows. So that could be the black that you're seeing. If you see small dots under your plants' leaves, treat them with Neem oil, following package directions. The holes in the leaves likely were caused by caterpillars or rose chafers, both of which also can be treated with Neem oil, which also works to resolve fungus and diseases.

So, to recap: Change your watering practices, consider sun exposure and treat with Neem oil. Good luck!

DEAR JESSICA: When is a good time to transplant iris? --Jane Cortale, Southold

DEAR JANE: That depends on what type of iris you have. If you have bearded, Siberian or Japanese irises, which have rhizomatous roots, you can dig up and transplant anytime from July through September. This should be done every three to five years to ensure they keep blooming well. If you have Dutch iris or reticulate iris, which have bulbous roots, you should transplant them in fall, when you would plant other bulbs.

DEAR JESSICA: I'm wondering whether there is a way to prevent, control and get rid of pine sawflies using organic methods. --Sal, via email

DEAR SAL: Yes! If the infestation is not severe, you can effectively destroy sawfly colonies simply by pruning off affected branches and disposing of them in the trash. For bigger infestations, you can avoid chemicals by using a biorational pesticide such as azadirachtin, horticultural oil, insecticidal soap, pyrethrins or spinosad. While perhaps not truly organic, biorational pesticides are naturally derived and deemed to have "limited or no adverse effects on the environment or beneficial organisms," as cited in "The Pesticide Book," by George W. Ware (1989).

Tomato Challenge

Evan Gottesman, 8, of Farmingville, and his grandpa, Sal Ferrante of West Islip, started tomato seeds -- and peppers, beans, cucumbers and beets -- indoors, then Evan transplanted the seedlings to his square-foot outdoor vegetable garden. We're looking forward to meeting Evan and his grandpa later this summer at the Great Long Island Tomato Challenge.

Are you in? Mark your calendars: This year's contest will be held at 7 p.m. Aug. 23 at Newsday headquarters (235 Pinelawn Rd., Melville). Give your plants plenty of tender loving care all summer long, then bring your biggest, heaviest ripe fruit to the event. Garden Detective Jessica Damiano will weigh your tomatoes personally and crown the 2013 Tomato King or Queen.

In the meantime, send a photo of yourself with your tomato plants, along with details about your growing strategy, to jessica.damiano@newsday.com, and you might be featured next.