There’s a whole group of wonderful plants that have fallen from favor in American gardens — biennials. The reason why is not hard to fathom, because there is so much confusion and misinformation out there about how to grow biennials that the average gardener just throws up his or her hands and heads for the far more comprehensible displays of annuals and perennials. Besides, who wants to invest in a plant that won’t even bloom the first year, and then dies the second? The answer to that question is you do, and here’s why: if you’re a fan of cottage gardens and wanted to identify one surefire design element that makes them “cottagey,” I’d argue it’s the heavy use biennials in these gardens. Because biennials seed themselves once established, they randomly appear in places where you’d never think to place a seed, but which bind and hold the more established plantings together in a wonderfully artistic fashion. In addition, many of my favorites, like Canterbury bells, hollyhocks, lunaria and foxgloves, bloom in that odd period right after the bulbs finish and right before the summer annuals and perennials start.
So what’s the trick to growing biennials? There are two, actually, and both very simple. Even though nurseries sell plants and seed in the spring, spring is NOT the time you should be interested in biennial species. Buy the seed now (and I would add, seed, not pre-started plants as they are expensive for species that so readily sprout themselves) stick the packets in the refrigerator in an airtight container, and forget about them until August. (This is a Zone 6 recommendation; adjust the timing up or down depending on the mildness of your autumn weather.) Then, as the gardening season moves into fall, find a couple of empty locations in the border, and sow HALF the seeds directly into the ground with a light 1/4″ covering of soil. Mark the spot with a stake to remind yourself there is something there, and make sure the area is irrigated in dry weather. (Some biennials, like foxglove, have very tiny seeds, so you may wish to start these in containers and then transplant them directly into the garden later.)
So what about the rest of the seed? Put the remainder back into the fridge until next spring, and then as soon as the soil can be worked, find a few more empty spots and repeat the process. If you revisit your fall planting locations, you will notice that your former seeds are now tiny seedlings that sprouted in the autumn, and then went dormant for the winter. These will bloom in the current season, which for clarity’s sake we’ll call year 1. The seeds you’ve just planted will bloom the next spring, in year 2. This double planting, which no guide ever mentions, is key to the process of getting biennials established in your garden: the first fall’s planting will self-sow for bloom the following year, year 3; year 2’s planting for year 4, etc. until the flowers appear every year as if they were annuals.
The second trick: be sure not to cut off the flower heads until the seeds pods have developed and opened. With species like lunaria, you’ll want to leave the decorate pods in place in any event, but you may be tempted to cut down the spent blooms of species like foxglove. You can indeed remove them, but not until the seed pods have opened. Then, as you cut the stalks, shake the pods out over the garden, randomly scattering the seeds to achieve that relaxed, cottage garden look.
Simple huh? Remember, you heard it first here!