The intensely seasonal nature of the greenhouse and nursery industry in our region means that many gardeners only shop for plants in spring and early summer. Planting early in the season lengthens the amount of time a northern gardener can enjoy a plant that year, so it makes sense that most of us don’t buy too many new plants after July.
But I think that September is really the best (read most economical) time to shop for perennial plants. I’m not saying that you’ll always find sales when you embark on your late season plant shopping adventure. In fact, I want to encourage you not to ask for deals on perennials if they aren’t already discounted. Most good garden centers will overwinter their perennial plants from year to year, which means they have nothing to gain from knocking down their prices.
Rather, I think September is an ideal time to buy plants because they have already had a few months to grow big and beautiful. September plants have been fertilized and watered regularly all season, and they’re practically bursting out of their pots, ready to go home with you. And, these containerized perennials can often be divided before you plant them! You can sometimes get three or four plants from a single pot, if the plant is large enough. I call these plants “Buy One, Get One” (BOGO) perennials.
Most perennial plants are easy to divide when they’re well-established in the ground. I just grab my good square-headed spade and dig, chop, replant. Dividing perennials right out of their pots requires more precision (and produces smaller plants), but it can be just as easy. I mostly reserve this technique for plants that have spreading rhizomatous root systems. Think of plants like daylilies or hostas, which spread by creating smaller versions of themselves, complete with their own root and shoot tissues. As long as you’re able to separate off an undamaged piece that has both types of tissue, you can propagate a new plant from the old one.
I usually use a digging knife to cut my perennials apart. It has definitely taken practice for me to feel confident doing this, so I would recommend practicing with plants that you’re not particularly attached to – like those old green hostas that seem to live in every yard. Find the natural space between two shoots and use the knife to pry the root tissue into two separate pieces. Some plants divide without much force, while others require a bit of sawing. If you end up with a chunk of root tissue attached to each shoot, you’ve succeeded!
Perennials filling up one- or two-gallon containers are usually the perfect candidates for this procedure. Common BOGO perennials include hosta, pulmonaria, monarda, daylily, astilbe, irises, stachys, turtlehead, sedum, allium, spiderwort, and rudbeckia. Again, perennial BOGO candidates have root systems that spread and then produce new shoots from their root tissue.
Don’t try to BOGO plants with single stems and/or large tap roots. It will be too challenging to break off pieces that have both roots and shoots, and you might just end up with lots of broken, damaged plant parts. Perennials that won’t give you an extra for free (at least not easily) include baptisia, aralia, amsonia, hibiscus, butterfly weed, and goat’s beard, among others. (Of course, there will always be some exceptions to all of my suggestions.)
The newly split plants will be small, but just be patient. Plant them as you would have planted the original one before you divided it. Give them a little extra water to help them establish, and then continue watering them regularly, especially if the autumn weather is hot and dry. Next spring, they’ll come up healthy and ready to grow.
Laura Schwarz gardens and writes in Minneapolis.
To learn more, join a webinar or workshop...