Ask the Gardener: Blossom end rot, bees, butterfly weeds and more

Gardening editor Doug Oster gets asked a lot of questions. A lot. And he doesn’t mind offering gardening advice. But rather than just limiting those answers to the person who asked, we thought it might be a good idea to share that wealth of knowledge with everybody.

There are three ways to send in your questions:

• Email askdoug@535mediallc.com

• Submit your question on our “Your Garden” section of our site

• Send us a message on Facebook.

(The questions may be lightly edited for grammar/clarity/etc.)

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Blossom end rot

Andrea: I have tomato plants in a pot on the deck. I only water once a week and even move out of the rain. I am noticing the tomatoes are rotting on the bottoms. What am I doing wrong?

Doug: That’s blossom end rot, and it’s caused by a lack of calcium. The thing is, it’s a watering issue. The calcium is probably in the soil, but the plant can’t uptake the nutrient if the soil is dry. Be sure the soil is evenly moist from now on. The tomatoes can heal themselves and often times later fruit will not be affected.

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Larry: How do I get rid of a ground nest of aggressive bees under a raised bed of veggies? Been stung twice mowing grass in that area, the first time (10-20 stings) I didn’t see what got me, the second time (6-8 stings) I saw they’re small bees that look a lot like flies. Their sting sticks with me for two painful weeks. I have no idea what kind of bees they are. I don’t want to use poison as they’re under a raised bed of strawberries, and I don’t have a clue what to do about them.

Doug: There are mint-based organic controls for ground bees. I would wait until it’s cooler (when bees are in a better mood) and apply it into the hole at the end of the day when most of the bees are down in there. Your local hardware store or nursery should have it in stock. One brand is Ecosmart, and another is called Safer.

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Linda: I put in a couple butterfly weeds this year, but to my knowledge, no monarch butterflies have been around. How do they know they’re here? Also, do I need to do anything to them to overwinter the plants?

Doug: There’s nothing you can do other than plant the butterfly weed and wait. I’ve got lots of plants to attract them and haven’t seen one either. It’s pretty tough and once established should come back year after year.

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Karen: I went out to water tonight and found three new Astilbe mowed down to the ground by bunnies. I just planted them in the spring, and they were thriving. If I keep the area watered, do you think they’ll be back next spring?

Doug: Yes, they should be fine. I would probably also feed them a liquid organic fertilizer like Grow from Espoma (available here). Keep the bunnies off with Hot Pepper Wax (also available here). Get the one that has a red pepper on the label, they make it in Greenville, and it works.

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Gilbert: The leaves are turning yellow on my tomatoes, and there are black specks on the leaves.What do I do? (I have been cutting them off.)

Doug: You’re doing the right thing. It’s a common problem with tomatoes when we’ve had this much rain. The only other thing you can do is treat them with Serenade (available here). It’s an organic fungicide. The disease won’t kill the plants, just slow them down. I’ve got it too, but I’m not treating them. The tomato fruit will be fine.