Wander around the allotments in the summer months and note the few plots with long lines of lovely marigolds between the rows of fruit and veg. Awww… such a nice thing to do to brightens things up – yes… and no. These canny plot holders are just carrying on a tradition that scientists have only now managed to catch up with – deterring whitefly.
In a recent study, those fine folk at Newcastle University wanted to see whether or not marigolds did indeed deter whitefly and if so why. And whilst these allotment holders already knew this to be the case, it really does need some scientific muscle to actually demonstrate, through careful study and more importantly evidence, that this really is the case.
The research and methodoloy is very interesting and provides actual evidence, not anecdote, for the benefit of companion planting.
It comes down to the fact that marigolds release a substance called Limonene into the air and as this wafts about plants close by (i.e. your precious tomatoes etc.) it deters the whitefly from the immediate vicinity as to them the smell is, well, horrible.
In other words if you plant marigolds next to your precious crops, you will get less whitefly and now it has been scientifically proved. Or to put it another way… always keep an eye on what your allotment neighbours especially if their tomatoes are doing much better than yours!
- How the humble marigold outsmarts a devastating tomato pest (Newcastle University)