Nasturtium leaf infested with aphids. Photo: cuckoosvegpatch.wordpress.com
In organic gardening books and web pages, the nasturtium (Tropaeoleum majus), a popular annual, is often touted as an ideal companion plant, used to repel aphids (greenflies). But that advice may do more harm than good if you stop at just planting it.
The nasturtium is actually what is known as a trap crop (also trap plant or sacrificial plant) … it doesn’t repel aphids, it attracts them! So, if you simply plant it as a companion plant, it won’t solve your aphid problem, but may in fact worsen it. That’s because once aphids settle on a nasturtium, they can easily make the jump to neighboring plants. This is especially true if there are ants in the sector (and aren’t there always?), as ants feed on aphid honeydew and literally farm them. They won’t hesitate to carry their aphid cows to the vegetables right next door, moving them to “greener pastures.”
So, the real use of the nasturtium in a vegetable garden is not as a companion plant, but as a trap crop. When you see aphids on the nasturtium, you simply have to pull it out and destroy it, nipping the infestation in the bud.
It’s a simple step, but a necessary one.