If you have just one little empty spot in your greenhouse, I would consider planting just one or two peppermint plants. Peppermint does grow outdoors, this is true, but it grows profusely in the greenhouse.
I learned this by accident as for years I had planted peppermint outdoors and it did so-so. Mind you, our soil was very clayey, and thus cool, and it was the time before we discovered the wonders of plastic mulch.
One year, I dug up the best of the outdoor plants and planted them in the ground in one of our unheated greenhouses.
Almost overnight the plants flourished and, to my amazement, within a week the plants had grown twice their original size; a month later, the tops of the plants just about reached my knees.
Almost as a thank you for having been moved to peppermint-plant heaven, the fragrance the plants exuded was pure delight.
Sadly, the plants did not overwinter in the greenhouse (because of no snow cover), but I had enough dried peppermint leaves to enjoy as tea for several years.
Peppermint is considered to be a hardy perennial, but here in the Yukon it usually goes not overwinter. The plant can grow two- to three-feet tall including the flowering spikes, and it grows pale lilac flowers in the summer around late July.
Peppermint grows fine in a shady part of the greenhouse or near where the water source is as they like plenty of moisture.
Peppermint (and the mint family) originated from the Mediterranean regions. While all mints belong to the same family, they also include oregano, marjoram and sage.
Its main use is culinary and is often found in desserts or herbal teas. The leaves can be crushed to excrete their oil, which is often used as a flavouring.
To harvest Peppermint plants, they should be dried quickly or they may mould.
To air dry peppermint, tie them by the stems into tight bunches and hang them upside down in a paper bag, in a dark place. The area should be dust-free and well-ventilated. In one to two weeks, the leaves will be dry and crumbly.
Peppermint plants are even available in various “flavours”. Try chocolate peppermint and lemon peppermint. These plants are a delightful addition to your greenhouse.
Ingrid Wilcox operates Lubbock Garden and Floral Consultant and offers gardening, greenhouse and flower-arranging workshops. Contact her at firstname.lastname@example.org.