Q: We're sharing a photo of fall mums that we bought at a box store during fall a year ago. Instead of composting them when they were done blooming, we planted them in the garden to see what would happen, and they survived. The picture is how they look now, with gorgeous flowers. Last winter was mild, of course. -- Janet and Larry Carlson
A: Your mums are beautiful! Mums, short for chrysanthemums, are perennials, but they are definitely borderline in winter hardiness in Northern regions. Cultivars vary widely in survivability, and many types sold as potted decorative plants every fall lack the ability to survive winter.
I'm often asked if potted mums can be planted outdoors when their pretty flowers fade and they no longer grace doorsteps and porches. I usually suggest trying it, since there's little to lose, and plants often surprise us.
Thanks, Janet and Larry, for sharing a success story. It proves that planting potted mums in the fall can be successful, providing beauty a year later.
As mentioned, some mum cultivars are more winter-hardy than others. The University of Minnesota has a long history of breeding mums with a better likelihood of winter survival. Included is the Mammoth Series and the Minn Series, such as Minnautumn, Minnyellow, Minnruby and others. Locally owned garden centers often sell starter plants of these in the spring.
Planting in May gives the mums the entire growing season to develop roots and a sturdy structure with a better chance of winter survival. By fall, the spring-planted mums become large and bloom profusely.
Whether we're planting decorative potted mums in fall, or starter plants in spring, mums survive winter best with their above-ground portion left intact. Cut back in early spring before new growth starts. Because most mums are borderline in hardiness, 12 to 24 inches of protective leaf or straw mulch also aids survival.
Q: How often should my Karl Foerster grass be divided, and is now a good time? -- Amber M.
A: Karl Foerster is the most commonly grown ornamental grass in the region, and for good reason. It's fully winter hardy and produces attractive seed heads that beautify the landscape from mid-summer through winter.
There's no definite protocol for how often the clumps of grass should be divided. Let the growth habit be your guide.
If the center of the grass clump dies out, and all the healthy growth is on the outer perimeter, then the grass would benefit from digging and dividing. Early spring is the preferred time, before new shoots begin emerging from ground level.
To divide ornamental grass clumps, cut the grass back to about two inches above soil level, dig the clump, and separate into divisions with a spade, knife or saw. Each clump can easily yield three or four healthy divisions for replanting.
Q: I bought some tulip bulbs on an end-of-the-season clearance. Is it too late to plant them, or should I store them in the garage until next spring? -- Kathy C.
A: Go ahead and plant the tulips; they're much better off in the ground than in the garage. Tulips can successfully be planted very late in the fall, and they'll still bloom next spring.
The preferred time would have been a month or two ago, which would have given the bulbs a longer time to settle in. To give the bulbs additional weeks of unfrozen soil, after planting be sure to water the soil well, and then cover the planting area with at least 12 inches of leaves or straw.
Adding a layer of protective mulch will keep the soil frost-free for additional weeks, giving the bulbs extra time to produce roots in preparation for next spring's bloom.