I love nasturtiums, however, when I grow them from seed in May, they grow beautifully and when they flower, they get infested with big ants that leave all their excrement on the stems and it is just gross. That not only affects the blooms but the foliage as well. I hose it off but the ants come right back. I have spoken to nursery people who have never heard of this happening. What can I do? Janice
This is a good news, bad news answer to your question. The good news is the ants are not harming your plants, but the bad news is the ants are there because of the aphids which are harming your plants. I'll explain. Nasturtiums have sweet nectar (sap) within the plant that attracts aphids. Aphids puncture the outside of the plant and passively feed on the sap contained in tubes called phloem within the plant. Once punctured, the sap is forced into the aphid's food canal and when digested, is excreted as a sticky substance called 'honeydew'. Ants love honeydew! In fact, ants love honeydew so much that they actually guard and herd aphids like sheep (called 'farming') to collect the most honeydew possible.
In your case, the 'excrement' that you see is actually black aphids, but aphids come in other colors too such as green, orange, white and wooly. There are about 4,400 species of aphids known. Nasturtiums are usually planted as a sacrificial 'trap crop' near vegetable gardens to lure sap-sucking insects like aphids, spider mites, whiteflies and leafhoppers away from the vegetable crop.
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About Linda Lillie
Linda K. Lillie is the President of Sprigs & Twigs, Inc, the premier
landscape design and maintenance, tree care, lawn care, stonework, and carpentry
service provider in southeastern Connecticut since 1997. She is a graduate of
Connecticut College in Botany, a Connecticut Master Gardener and a national
award winning landscape designer for her landscape design and landscape installation work.