Can fall mums be planted in the garden?

Brightly colored fall chrysanthemums, or “mums,” are hard to miss as summer winds down and fall approaches. They can be purchased just about any place that sells plants, from garden centers to grocery stores. The popularity of mums is easy to understand, as they add a pop of color to the garden or porch just as most other blooms are starting to fade, and there is surely a color that will appeal to every gardener’s taste. It’s easy to find mums in fall hues of yellow, bronze, purple or burgundy, but they also come in white, pink and red. These plants can either be planted in containers and hanging baskets or stuck into the ground to fill gaps in the garden. Regardless of how they are used, do not expect them to survive the winter. The fall blooming mums that can be purchased late in the growing season have not been bred for cold hardiness. If they do manage to live through the winter, they seldom bloom again. It is almost always easier to treat them as annuals and add them to the compost heap after the first hard frost.

However, there are some mums that are hardy enough to grow perennially in New Hampshire gardens. These so called “garden” mums are typically hardy in Zone 5 but may require extra winter protection. Some of the single-flowered varieties like ‘Sheffield’ (Chrysanthemum ‘Hillside Sheffield Pink’) or ‘White Bomb’ (Chrysanthemum weyrichii ‘White Bomb’) are hardier than the double florist varieties. To give these plants the greatest chance of survival, plant them in the spring so that they have the entire growing season to become established before winter. Choose a spot in the garden that has rich, well-drained soil and full sun.

Garden mums can be made more attractive by “pinching” them once or twice between Memorial Day and the end of June. To properly pinch a mum, remove one inch of the tip of each branch or shoot when plants are 6-8 inches tall. Pinch a second time when the resulting new shoots reach 6 inches in length. If pinching does not happen, mums may become top-heavy and require staking to keep them upright.

Occasionally garden mums do winterkill, especially if the soil drains poorly or if there are excessive temperature fluctuations in the winter. Since mums have shallow root systems they are very easily damaged by freezing and thawing. This type of winter damage can be prevented with mulching and proper care in the fall. Garden mums are much more likely to survive the winter if the dead plant stems are not removed until the spring. Additionally, adding a 2-4-inch layer of mulch over the crowns of plants can help. Pine needles, shredded bark, clean straw or evergreen boughs work well, but avoid leaves as these flatten and provide very little insulation. Remove the mulch once the ground thaws in April and cut back dead stems before new growth begins.

If successfully growing hardy garden mums sounds like too much effort, stick to annual florist types, or try planting other fall blooming perennials to extend the bloom season in your garden. Asters (Symphiotrichum species), ironweed (Vernonia sp.) or sneezeweed (Helenium autumnale) are all excellent choices for New Hampshire gardens.