I took Mrs Dershley, my neighbour, a bunch of marigolds today to say thank you for the choc chip cookies she baked for me. Not just any marigolds - Mexican marigolds: Tagetes erecta. Now, you’re probably as surprised as she was at my choice of flower. They are quite stinky, after all. And we’ll say this softly so we don’t hurt any marigold’s feelings, but in my opinion, they really aren’t the prettiest flowers around. But my mother always said that a marigold is worth a dozen roses. Mrs Dershley asked me why my mother always said that and I found that I couldn’t explain, I just always took my mother’s word for it. So I dug into the sparse scientific literature on this weedy plant that grows pretty much everywhere.

The Mexican marigold’s claim to fame is its ability to repel things. That’s not surprising, it’s nearly stinky enough to repel humans. I hope I don’t repel Mrs Dershley - I would love some of her choc chip cookies again. Anyway, it chases away certain microscopic worms called nematodes that live in the soil and make plants sick. It also repels certain insects (like mosquitoes), and the roots have been proven toxic to the mosquito’s distant cousin, the house fly. I’m wondering. If house flies don’t like marigolds, they may be useful to keep around.

What I didn’t know was that the flowers are edible. They are not only edible, they’re packed with all kinds of healthy goodies. Take a deep breath. They are antibacterial, antimicrobial, antioxidant analgesics that can protect your liver and be used to promote wound healing.
Marigolds have a pretty intense colour and are used as food dyes. One of their main pigments, lutein, helps protect your eyes from getting macular degeneration later in life.
They may be good for me, but I just can’t envision myself eating marigolds in my salad every day. I want to find out whether they repel flies… that would be just incredible.


Want to dig deeper? See if you can find the answers to these questions:
1. What other plants are commonly used to repel mosquitoes?
2. What is macular degeneration?
3. What is an analgesic?

Feeling creative?
Gather some Mexican marigold seed and plant some in a spot in your garden where they will look pretty. You could even paint a flower pot a pretty colour and plant some in the flower pot, then put them on your window sill to keep the mozzies away.

Practical project:
Professor Snippet couldn’t find an answer anywhere in scientific literature as to whether the flowers of Mexican marigold repel house flies. He reckons it’s time to set up an experiment, although this is going to get a little bit gross.
1. Find some kind of food that is going to attract flies - this could be leftovers or raw meat, or anything else you think may work.
2. Divide the food into two equivalent portions.
3. Place the food onto two plates and put them somewhere outside or in the kitchen (keep a meter or two between the plates). Also put a third, clean dish there.
4. Now place Mexican marigold flowers all around the one plate with food and none around the other plate with food.

Your experiment consists of three things:
a. A negative control - that is the clean plate. This shouldn’t attract any flies. Biologists always have a negative control to check that the obvious things are working.
b. A positive control - that is the food plate with no marigolds. This should attract flies. If it doesn’t, you know your food is not attracting flies as it should. It also gives you something to compare to.
c. Your experimental plate - this is the food plate that is actually testing whether the marigolds repel flies. You will need to observe for a while (as long as you have patience for) and compare the number of flies that visit this plate against the positive control. If it’s less, then the marigolds are repelling them. If not, the marigolds have no use as a fly repellent.

If you’ve done this experiment, please comment below. Professor Snippet is curious to know your results!