The problem with planting them too close is that they will grow together and *you* won't know which plant is which. Especially keep the pennyroyal away from the culinary mints - pennyroyal has toxicity concerns.

FataMorgana

Actually according to some herb authorities, mints can and do cross-pollinate. It is suggested that you grown them apart. If you have a problem with different mint types cross-pollinating, or if the plants are reseeding prolifically, cut off the flowers. And keep the pennyroyal away. It has been used traditionally to induce abortions and can be dangerous if ingested.

According to the Encyclopedia of Herbs and Their Uses by Deni Bown, page 386, she states the following:

. . . certain herbs may cross-pollinate, giving rise to seedlings that differ from the mother plant. When various kinds of thyme (Thymus supp.), marjoram (Origanum spp.), mint (Mentha spp.), and lavender (Lavandula spp.) are grown near each other, the chances of hybridization are high. Closely related genera may also interbreed if they are grown together and flower at the same time; dill and fennel are known to cross, resulting in plants that are indeterminate in flavor.

See Mints which states the following:

Different varieties of mint should be planted as far apart as possible, as true mints hybridize easily, cross-pollinating when in close proximity. The resulting hybrid combines the characteristics of both parent mints in a way that may not be favorable. If you grow both peppermint and spearmint, start them at opposite ends of the garden in order to maintain the integrity of both.

Cross-pollination affects only the next SEED generation. Those would be the hybrids. It will not change the PLANTS that you intend to install. As long as seeds are not collected and germinated for a future crop, you need never worry about the pollination activities.

In other words....some plants can cross pollinate successfully like crazy! It won't affect the flavor or anything else about those plants. Only the plants that you may grow from seeds you've collected from those original plants will express that new 'hybrid blood line'.

That is true rhizo. I guess that I really didn't make myself clear about planting and cross pollination. Thank you for your clarification.

However as a rule of thumb down here in far south Texas, where our herbs basically grow year round unless we get a rare hard freeze, we do not recommend planting herbs that can cross pollinate close together unless you intend on cutting all the blooms off. This is basically for precautionary purposes to protect what "might" come up as a hybrid.

For example, a friend of mine from a northern state, moved here and planted 4 different varieties of mints in an old whiskey barrel. It wasn't too long before she realized that she had only one type of mint because of cross pollination.

I do have a small bed of mint with 3 different varieties which has been growing non-stop for about 6 years now. But since it is small, I go out and cut off all of the blooms to prevent the possibility of cross pollination.

And one of our Master Gardener demo gardens was left unattended for about a year, and before we knew it we had a whole bed of "?". So we started investigating, and it turned out that the dill and fennel, which had been planted closely together, had cross pollinated with the end result being something no one wanted to us. So we do not recommend planting cross-pollinating plants too close together for this reason.

Sorry for any misunderstanding.

Thanks for the replies everyone! The closest 2 types will be together is about 9 ft. I'll snip the blooms just to be safe. I thought it was fascinating that something classified as "sterile" could pollinate anything at all.

Your mints can't, as you say, be both sterile and cross pollinate. But not all mints are sterile by any means and if they're not they can breed! I'll re emphasise what others have said. The flavour of the original plants is not affected by cross pollination. It only becomes an issue if the cross pollination results in seedlings. They can be variable. So, as you plan, cut off the flowers if you don't want mongrel mints in your garden.

Can mint and basil cross-pollinate? I've had mint growing for years and planted a basil plant not far from the mint just a few weeks ago. I discovered yesterday that it had begun flowering; I pinched the blooms off and discovered the plant smelled peppery/minty and not like basil at all. Is this due to flowering (and if this is the case, any hope at getting my "old" basil back without replanting altogether?), or could it be that it's cross-pollinated with the mint? Is that possible? Or, as flora_uk said, any cross-pollination wouldn't affect the original plants, only hybrid seedlings? I'm a gardening novice. :-)

I do know that italian parsley and chives shouldn't be planted togerther. The new plants are WEIRD

"a friend of mine from a northern state, moved here and planted 4 different varieties of mints in an old whiskey barrel. It wasn't too long before she realized that she had only one type of mint because of cross pollination."

Cross-pollination had nothing to do with that. What happened is that one of the varieties was so vigorous is crowded the others out and killed them.

As for the basil ... mint will spread with underground runners, so you probably have mint there, not a hybrid.

"I do know that italian parsley and chives shouldn't be planted together. The new plants are WEIRD". Not sure where you got that information, Bellashere. Do you have a reference? The only reason I can imagine for that advice is that chives are perennial and stay in one spot undisturbed, while parsley is biennial so requires some disturbance every year. There is no way they can cross pollinate and produce seed as they are in entirely different plant families. You might as well be discussing the offspring of a pig and a cat. So the concept of 'new plants' is just nonsense, I am afraid.

I was looking for info on mint cross pollination and came across this thread. Thank you for the great info. I would like to chime in about pennyroyal: This plant makes a lovely, tasty tea that I drink all the time. Yes, it's an emmenagogue (encourages menstruation), so I might avoid it when pregnant, but otherwise the tea is just fine to drink as a beverage and is also medicinally valuable.

The case of pennyroyal toxicity that everyone has heard about involved pennyroyal essential oil. Essential oils are extremely concentrated plant extracts, and shouldn't be taken internally unless you really know what you're doing and are being very careful with dosages. But there's a big difference between an essential oil and a tea!

All mint varieties grown commercially at scale for any kind of culinary use or nursery sale are propagated vegetatively. That includes spearmint, peppermint, and all of the various flavored mints like orange and chocolate. They are hybrids that don't grow true-to-type from seeds. Nearly all of the flowers from most of these varieties are sterile, so you probably don't need to worry about untrue volunteers popping up from seeds. But if you want to be sure, cut off the flowers. As long as you aren't getting volunteers or collecting seeds, cross-pollination is a moot issue with these mints. Cross-pollination only affects the next generation grown from seeds.

Only a few traditional mint varieties such as mountain mint and Korean mint grow true-to-type from seeds. For these types I suppose cross-pollination could be an issue. If you buy mint seeds described as spearmint, peppermint, or just "mint", they will probably yield mint plants that don't smell or taste very good.

When shopping for mint, make sure it smells as good as you imagine it should. Peppermint should smell like the candies, and spearmint like a mint sauce, with no unpleasant odors mixed in. I've found many small organic farms selling some pretty bad smelling and tasting mint at farmers' markets that must have started somewhere along the line from random seeds, instead of from the desirable commercial hybrids. Nursery plants and cut mint at produce markets or grocery stores are mostly good. You can root cut mint in water or potting mix.