Question for Mary:
I have a query regarding succulents. I bought two tiny cathedral plants about 30 years ago on Canal Street in New York. They grew into a huge gothic cathedral, so beautiful, 11–feet tall in my livingroom. Had to cut off the tops, and now they are 11 feet tall, too. Very easy to propagate. Have given many away as beautiful gifts. About 20 years ago, when I finally weaned myself from topping noble firs for magnificent Xmas trees (they look splendid in our Edwardian flat with its tall ceilings), I started decorating the cactus, and it looked marvelous too. However, about five or ten years ago, a thrip blew in, and I have gone the rounds trying to get rid of it “organically”: Neem, purchasing an electric atomizer, even letting hundreds of lady bugs loose in the flat (never do this!), but I cannot seem to stop the infestations. I may have to compost entire plants… Any advice?
Answer from Pat:
Cathedral plant (Euphorbia trigona) grows extremely well as a houseplant, but needs occasional diluted fertilizing during the growing months, in addition to well-drained soil, and adequate light with no direct sun. I have seen several huge ones growing indoors. Due to this euphorbia’s multi “trunks” getting rid of a persistent pest such as thrips without spraying is more than a challenge, it’s nigh impossible. Luckily, Spinosad will control thrips. This is an OMNI-registered product and so it is safe to use indoors and since there are no bees indoors it can’t hurt anything. Nonetheless, one should take care to protect your lungs and not to breath in the product while spraying. (Covering a large plant with a big shopping bag or large trash bag while spraying can help accomplish this.) Also clean up and replace the the top 1/4 of the soil or rock in the pot. You may need to spray more than once. Out in the garden thrips are best controlled by beneficial insects but I can just imagine what it would be like to release lady bugs inside the house. A noble idea with tragi/comedy results.
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