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Ask a Master Gardener: Rosemary fights pesky fruit flies

by Peter Sutter | September 3, 2022 at 4:00 a.m.

This time of the year, tomatoes, pears, apples and cantaloupe are being harvested pretty regularly, and no matter how hard a person tries, those pesky fruit flies seem to abound around the ripe fruit.

A few years ago, I read putting a couple of sprigs of rosemary on a compost pile would help keep the flies under control. My wife decided to put a sprig of rosemary in the fruit bowl and presto, no fruit flies. So now, wherever we have tomatoes or other fruit, we lay a rosemary cutting on them. Now rosemary is a regular in the herb garden. What a difference it has made.

Rosemary is not just good for keeping the pesky little fruit flies away, it can also improve memory. It turns out there are compounds in rosemary oil that may be responsible for changes in memory performance. One of them is called 1,8-cineole -- as well as smelling wonderful (if you like that sort of thing), it may act in the same way as the drugs licensed to treat dementia, causing an increase in a neurotransmitter called acetylcholine.

These compounds do this by preventing the breakdown of the neurotransmitter by an enzyme. And this is highly plausible -- inhalation is one of the best ways of getting drugs into the brain. When you eat a drug, it may be broken down in the liver which processes everything absorbed by the gut. With inhalation, small molecules can pass into the bloodstream and to the brain without being broken down by the liver. So be sure and crush a few of the sprigs you have laying around to get the aroma therapy benefits.

Growing rosemary from seed can be trying -- this I know from experience. Rosemary seeds are fairly difficult to germinate, and the seedlings are slow to grow at first. Growing the herb from seed is a time-consuming process. And of course it is a little late to buy a plant this year, so this might be something to plan on for next year.

Another option, if you can find someone with a plant that is willing to give you a snip-it, clip a 3-inch cutting from the tip of a stem, remove the leaves 1 inch from the base, apply rooting hormone on the exposed portion of the stem and put it in potting mix. Roots will emerge within a few weeks. Transfer to a larger pot or directly to your garden (next spring).

If you would like to grow your own, here are a few tips. First, although rosemary is a perennial in warmer climates, it is grown mostly as an annual here in Mid-Missouri, but I have been able, with special care, to get a plant through the winter. That being said, it is probably more suitably grown in a pot in our area so it can be taken in during the winter months.

Some rosemary varieties can grow to 5-6 feet tall, so if you're growing rosemary in pots, "Blue Boy" is a small bush rosemary with proportionally small leaves that grow in clusters. "Golden Rain" is another variety that stays compact and small.

Rosemary will need 6-8 hours of sunlight per day, so a south facing window would be an ideal place to grow it while inside.

Water rosemary plants when the soil is completely dry. Be careful not to over-water and avoid making the soil soggy (especially when growing in containers), as this leads to root rot. Next spring, you can transfer your plant directly in the garden or set it outside as a container plant.

I hope you will include rosemary in you garden plan for next year and join the "fruit fly battle." Oh, I almost forgot to mention -- rosemary is good for cooking, too.

Happy gardening!

Peter Sutter is a lifelong gardening enthusiast and a participant in the MU Extension's Callaway County Master Gardener program. Gardening questions can be sent to [email protected]

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