How Far Apart to Plant Herbs to Keep Their Flavours from Changing
Answered by: Conrad Richter
Question from: Sherry McAlister
Posted on: March 28, 2008

Can you please tell me how far apart I need to plant varieties of basil so that they can keep their individual fragrances and tastes? Same question regarding mints and scented geraniums. Thank you for helping me out with this.

This is a good question because people do get confused about the effects of herbs on each other when planted close together. The short answer is that you don’t have to worry about basils and scented geraniums, but you do need to worry about the mints. But there are several important points here that are worth delving into.

The first point that needs to be made is that herbs planted close together do not alter the fragrance or flavour of other herbs -- at least not directly. But it is possible that a tall herb will crowd out a smaller herb so that the shading effect reduces the intensity of the smaller herb’s fragrance and flavour. Or a more aggressive herb will outcompete a neighbouring herb for nutrients and water causing changes in the latter herb that affect scent and taste. These scenarios are possible -- but in truth they probably happen only rarely. For my money the only universal concern that applies to all herbs is: do the herbs have enough space to grow without overcrowding each other; and I do not worry about changes to taste and flavour.

Now it is true that some plants can affect neighbouring plants by exuding chemicals from the roots to the soil or from the foliage to the soil and onto the leaves of neighbouring plants. But these cases are very rare. For basil, mints and scented geraniums, there is no such effect.

Some plants require cross pollination to get fruits or seeds and they are dependent on their neighbours. You do see this with certain fruit trees and vegetables. It is possible that the pollination process causes some changes to the essential oils (which are responsible for the scents and flavours) but we never see that in basil, mints, scented geraniums, or any other of the common herbs. But it is sometimes true that the scent and flavour can change when herbs form seeds. This is why we recommend harvesting herbs just as the flowers begin to appear, well before the essential oils degrade as the seeds are developing.

There is one scenario where planting too close is a real concern. When mints are planted close together you can get cross-pollination and seeds to form. These seeds can fall to the ground and produce new plants. Almost always the child plants will have flavours and scents that are inferior to those of their parents. The child plants may look just like the parents but the essential oils can be totally different, and the flavours will likely disappoint you. This does not happen with all mints because they don’t always cross-pollinate, and some do not produce seeds at all (e.g. peppermint); but it happens enough of the time that you probably should keep your mints as far apart as possible. And besides, mints spread so quickly that different varieties can easily get mixed up making a mess of your mints.

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