Marigold, originally uploaded by dhickie.
One of the best things about planting a marigold or two in our aquaponics system would have to be the wonderful burst of yellow that greets us everyday when we look at our lush beds. Marigolds are more than just beautiful though - traditionally Marigolds are planted in the garden because of their beneficial qualities. French marigolds have a very strong odor which confuses pests, and their roots give off a substance which repels nematodes.
Don’t quite know your nematode from your left foot? Well, a nematode is a tiny (microscopic) lifeform. They are the most abundant multicellular lifeforms on earth. In a teaspoon of garden topsoil there might be millions and millions of nematodes. “Depending on the species, a nematode may be beneficial or detrimental to a gardener’s cause. From a gardening perspective, there are two categories of nematode: predatory ones, which will kill garden pests like cutworms, and pest nematodes, like the root-knot nematode, which attack garden plants.” Wikipedia. So in a traditional soil based garden, you plant marigolds to repel ‘bad’ nematodes which build up in the soil after some crops such as tomatoes.
So how effective are marigolds in an aquaponics system? So far, we’ve noticed a few interesting things. Firstly, the green caterpillars that are our current uninvited dinner guests every night seem to love eating Marigolds even more than they like eating our plants. So they seem to be drawing the pests away. Additionally, the caterpillars seem to want to cocoon in the Marigold leaves - another service to our other more desirable food crops. And as I learned on the Milkwood Permaculture course I did earlier this year, its not always necessary to have a pest-free environment. It’s better to have an environment that supports life, a balanced system, rather than a sterile system devoid of insect life, so admired by farmers who farm monoculture crops.
There is always the chance that the Marigolds we have are hybrids, and are therefore less effective than the older and stronger varieties. As for the nematode repelling qualities of the root system, that’s an interesting question when it comes to aquaponics, a non soil based system. I’m assuming there are nematodes in the gravel beds, but since the system flushes out every hour or so it wouldn’t be the same as a soil based garden, which would naturally see some build up in soil substances. Classic gardening concepts such as crop rotation address this particular issue of how to organically balance soil nutrients. In terms of nematode build up though, I don’t yet know much about this area and I’m keen to look into it over the next few weeks.