Inside The New York Botanical Garden

Mum’s The Word

Posted in Gardening Tips on October 11 2011, by Sonia Uyterhoeven

Chrysanthemum 'Cockatoo'
Belgian mum 'Cockatoo'

Weather generally has the upper hand when it comes to gardening. There are lots of things we can do to foster the care of our plants, but ultimately we end up at the mercy of Mother Nature. This year was no exception. The New York-area had a wet spring, baking hot July with no sign of rain, and then a record-breaking, near-constant deluge in August.

And now we’re seeing the effect of this weird weather around the Garden; many of our fall bloomers are one to two weeks behind schedule, most notably our late September rose display and our chrysanthemums. It has also been a lousy year for tomatoes.

In July, when the temperatures rose into the high 90s and we lacked any rain, our plants responded by shutting down. This is a protective response which helps them survive difficult times. If the plants had continued to push growth under these conditions they would have lost too much moisture and wasted a dangerous amount of energy. In this respect, plants are just like people; they get sluggish and slow down in the heat.

After such a difficult and dangerous month, the rains of August were, at least initially, a welcome relief. Rather quickly the constant rain became too much as everything became supersaturated and waterlogged. Many plants continued to stall-out on growth. Finally, months later, they are picking and reviving, but they are way behind schedule.

Chrysanthemums were especially affected by these temperamental weather conditions. Typically during the long days of summer, chrysanthemums will put on a lot of vegetative growth. Once the days shorten they will start bud formation and blooming, but this year, due to the extreme weather fluctuations, they have been thrown way off schedule.

Mums are traditionally classified into categories depending on their flowering time: Very Early, Early, Middle, Late, and Very Late. In the New York City-area, chrysanthemum flowering typically spans from late-August through the end of October. Korean mums flower even later and extend into November.

Very Early mums have peak bloom from the last week of August into the first week of September. Early mums cover the middle of September for a two week peak, and the rest of the mums continue sequentially in two-week increments until  the end of October with the Very Late mums.

I gave a gardening demonstration at the opening of Fall Flowers of Japan where one participant asked for advice on finding and taking care of hardy mums. Here is my advice:

If you would like your mums perennialize, plant them early. Ideally, mums should be bought and planted in the spring so that they have an entire growing season in which to become established. This is generally not achievable, however, since most hardy mums are sold in flower in the fall. Therefore, it is best to buy your hardy mums as early in September as possible and to get them into the ground as quickly as possible so that they are able to establish a good root system before winter sets in.

Once in the ground, do not cut the mums back once they have finished flowering. We have experimented with this for years at the Garden. I have found that cutting hardy mums back hard in the fall results in a survival rate of only 60 to 70%. Leaving the mums alone or just trimming them back 6 to 8 inches results in a higher survival rate. Best yet, just wait until early spring to cut them back, this will prevent exposing cut stems to moisture that can become trapped in the crown of the plant allowing it to rot out.

Hardy Belgian mums are taking the market by storm, and are definitely a plant you should look for. They are hardy from zone 4 to 9 and are incredibly floriferous. They have a nice mounding habit, flexible branches that don’t break easily when handled, and require no pinching in order to retain a nice round habit (provided you give them with enough space to grow). People often do pinch them back juts once when they are very young, to get them going.

There are many different cultivars of Belgian mums on the market in a rainbow of colors. Some that we have grown or are growing in the Garden include ‘Atlantico Yellow’, ‘Carpino’, ‘Olawa Red’, and ‘Ilvico Orange’. There are so many varieties available that you can’t go wrong. The other week I had a Belgian mom attending one of my demonstrations, so we took her photo holding a white Belgian mum named ‘Cockatoo’.

The University of Minnesota has a hybridizing program for hardy mums that are also no-pinch and retain their nice round shape. You can recognize these varieties by their name; they have either the first or second half of the word “Minnesota” in their name, for example: ‘Lemonsota’, ‘Snowsota’, ‘Minngopher,’ or ‘Minnautumn’. Today’s wide selection of hardy mums combined with proper care, and a little luck in the weather department can have your garden awash in color in fall.