Writing about hardy mums in the spring may seem like an oxymoron. Let me explain.
For years I’d listened to homeowners say what bad luck they had growing perennial chrysanthemums. They’d plant the big showy mums every fall and rarely found that they survived the winter and grew the following year. Tired of failing, they’d stopped planting them or only bought a couple of plants to toss into containers for fall interest.
The issue of not being hardy has to do with timing and the roots.
When you buy a fully developed mum in the fall, it has grown in its pot in a greenhouse for most of the summer. When removing the plant from the pot you can see the massive tangles of roots that developed. Attempting to tease them apart before planting, in this case, does little to establish the plant. Your big cushion mum takes up water to make it through the fall but lacks the time necessary to set new roots deep enough to survive our Zone 5 winters. The chances of these mums returning the following spring is less than 30%.
Yes, I know some of you have had luck over-wintering these potted mums; you are the 30%. The other 70% of us are left with a stalk attached to a nicely compacted and thoroughly dead root mass.
The point here is when to plant mums. The hardy mums you see sold in the spring are the same cultivars you will buy, fully grown in the autumn. They are the plugs used to pot-up for the big containers of cushion mums in September.
Hardy mum cultivars for Zone 5 are root pernicious through our winters, unlike florist mums that are a perennial only in the southern regions of the country.
To grow hardy mums that return every year, pick an appropriate well-drained and sunny site and plant them now. Many hardy cultivars are available at local greenhouses, and a few mass merchandisers may carry them as well. By planting hardy mums in May the root system will have sufficient time to become established before winter.
Just before you plant your mum, remove the top one-third of the central stem and pinch-off tips to remove all buds and flowers. Mums are terminal bloomers, which mean they bloom on the tips of new growth. By pinching the tips the plant sends out side branches, leading to more tips for flowers in the autumn.
A rule of thumb for when to pinch back established mums is based on our holidays: pinch them back by half on Memorial Day, and again on the 4th of July. After the second pinching let the mums develop their buds.
Bud development is based on photoperiodism, meaning the length of the period of light and night. Mums growing in the garden flower as the days become shorter. This is why we see them in late summer and autumn.
As the years go by and your mums return each spring and spread, remember to keep them pinched back. With larger masses of mums I often use hand held hedge clippers to quickly cut them in half.
By following these simple rules in spring, you’ll have a beautiful colorful display of cushion mums as summer comes to a close.
And so now I think I’ve redeemed myself from having spoken of autumn when spring has only begun.
Copyright 2015 Margaret Rose Realy
Image: Chrysanthemum flower by kiya-nochka, at shutterstock.com.