This is the time of year when I start thinking about how I will overwinter my tender perennial spices and herbs. I grow a limited amount because I use insulation instead of heating and I have limited windowsill space inside and loads of competing plants.
The most tender Herb I grow is plectranthus amboinicus.
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Known by myriad names it's commonly referred to as Caribbean thyme in my house. Having tried over wintering in insulated boxes, under fleece in a Keder, sunk in hot composting matter - the most successful - I now root cuttings and grow on on a South facing windowsill. I reduce watering but make sure the compost don't dry out after nearly losing my entire supply a few years ago.
My African Blue Basil is next in order of difficulty.
A sterile hybrid it is nonetheless one of the most impressive pollinator magnet in garden an allotment. Propagated from cuttings it roots easily and grow fast. I have managed to overwinter in a insulated box in the Keder under several layers of fleece but pests took a heavy toll and the plants were slow off the mark in spring. I do two batches one on the windowsill sprayed regularly with homemade pest control concoctions and the other in pots sunk in compost. I usually get about half a dozen through which is enough to fill borders tubs and plots with this amazing herb.
Ginger and Tumerics are my 2 tender spices. I grow the small Jamaican ginger because it has a finer flavour and is hard to find. I grow these in heavily insulated covered boxes in my garden and the ginger have thrived over the years providing rhizomes and stems for cooking, baking, teas and soft drinks.
The plants die back in winter andand we lay fleece on top so we can continue to harvest rhizomes as needed.
Tumerics did not thrive, just limped along making very little rhizomes from year to year. It was only when l experimented with the construction of an insulated polytunnel that it found it's niche. We moved it into a box in the tunnel last year and was pleasantly surprised. It behaved like the ginger in the insulated box, making loads of healthy rhizomes., dying back in winter and then growing off to a early healthy start.
At the moment it is one of the successes of insulated polytunnel.
Other herbs are easier. Our Vietnamese coriander manages in sheltered parts of the garden with backup plants spending winters in the Keder while Lemon Verbena is well established in the micoclimates we have identified over the years.
We grow a great deal of herbs from Wasabi and dittander to fruity sages, mints and the usual Mediterranean ranges but the tender herbs are our greatest challenge as we continue to grow without using any heat source in garden and allotment.
