Background

Chrysanthemums, or mums, are hardy, fall-blooming perennials that create mounds of vibrant blooms that last long into the late fall. In most cases, mums are relatively simple to maintain, requiring little more by way of care than routine watering, feeding and pinching to sustain good growth and produce attractive blooms. There are literally thousands of different mums to choose from, each of which offers the gardener a unique set of attributes in terms of flower form, flower color, plant size, growing habit, hardiness and more.

Mums are short-day plants, which means that they redirect their energies and internal resources from the production of vegetative growth to the production of blooms as the days grow shorter. Tthat's why mums flower in late summer and fall. However, it's important to note that not all mums produce blooms according to the same timetable: Some begin blooming after 6-8 weeks of short days, others after 9-12 weeks. The early bloomers (6-8 week response group) tend to be hardy, self-sufficient types, while the late bloomers (9-12 week response group) tend to be bigger and bolder, but require much more hands-on care (frost protection, training, pruning, etc.).

How To Care for Mums

Planting. In cooler climates, mums can be planted from early spring through early summer, and again in late summer or early fall. In warmer climates, fall planting is generally best. If you live in the North and wish to plant in early spring, be sure to wait until nighttime temperatures can be expected to stay at 50 degrees F and higher.

• Select an open, sunny planting site with fertile, well-drained soil with a neutral to slightly acid pH, as well as an open, airy situation that affords them plenty of room to feed and grow. Soil with a pH below 6.0 or above 7.0 should be amended. Amend with lime if the soil is too acidic, sulfur if the soil is too alkaline. Space them at two-foot intervals when you plant. Cultivars with a mature height or one foot or less, however, may be planted closer together.
• If establishing a new flower bed, clear the planting site of weeds using a non-selective weed killer according to instructions, wait 48 hours, then cultivate the bed to a depth of six to eight inches, amending the soil with rich, organic materials such as compost or pre-packaged garden soils and planting mixes.
• Dig a separate hole for each plant in your bed, then set plants in holes so they are level with the surface of the soil. 
• When backfilling a planting hole, do so carefully and evenly to eliminate air pockets. If using a slow-release plant food, mix it into the backfill soil at time of planting.
• Water thoroughly immediately after planting.
• Add a two to three-inch layer of light, organic mulch around your new plantings to defend against weeds, help retain moisture and keep the ground cool.

Watering. Mums have average water needs, requiring about one inch of moisture per week through rainfall or watering. Keep the soil moist at all times, but never saturated or soggy. Be sure to check your plants regularly during hot and/or dry spells as mums suffer badly under drought conditions. Discontinue watering after the blooms show color.

Feeding.  If using a slow-release plant food, mix it into the backfill soil at time of planting. Otherwise, sprinkle a granular fertilizer around the plants after planting, or feed weekly with water soluble plant food. To feed large areas, use a hose-end feeder. About three to four weeks prior to expected bloom, switch to a high-phosphorus water soluble plant foods specially formulated for bloom development to give your mums the nutritional boost they need to flower abundantly and vibrantly.

Deadheading: Promptly remove spent flowers while your mums are in bloom in order to prevent them from setting seed. This will not only stimulate increased bloom production, but also help lengthen the plant's bloom cycle.

Pinching: Mums should be pinched back periodically during the growing season to promote fuller, bushier growth. To pinch back, use your thumb and forefinger to nip off the top (or apical) bud from each stem. This will force the plant to redirect its growth from vertical to horizontal, leading to the generation of three lateral shoots (or breaks) wherever you have pinched.

How often you pinch your plants will depend mainly on how you want them to grow. To encourage tall, lanky growth, pinch back infrequently- just often enough to help the plants retain a somewhat natural shape, or even less often if you want the plants leggy and you're willing to stake them. To foster full, bushy growth and bigger flowers, though, pinch back frequently throughout the season, starting when the plants are six to eight inches high and continuing until they are within two to three months of blooming.

Disbudding. To produce huge, specimen-quality blooms, disbud your mums by removing all but one or two flower buds from each stem's cluster. For one high-quality flower per stem, snap off all side shoots and side buds, leaving only the central bud in place.

Mulching. A protective two to four-inch layer of light, organic mulch around the base of plants is recommended to prevent encroachment by weeds, improve moisture retention and, most importantly, stabilize soil temperatures over winter. Mums have shallow roots and are therefore highly susceptible to frost-heave, so mulching is critical if you want to keep them from being uprooted.

Insect and Disease Control

Mums, as a rule, are fairly resistant to serious insect problems, but at least few widespread garden pests can occur. To control the insects described below (except slugs and snails), treat plants with insecticidal soap, neem oil, pyrethrin or other insect spray.

Aphids. The appearance of thin, anemic-looking stems and discolored, sometimes stunted leaves are evidence that aphids have infested the garden. Aphids are probably the number one pest problem for mums. For best results, spray both sides of leaves as aphids and other destructive pests (e.g. spider mites) like to live on the underside of plant foliage.

Red Spider Mites. Brown flecks on plant leaves tell you that spider mites have been dining on the foliage of your mums.

Leafminers. White, light green or brownish colored lines or blotches on plant leaves indicate that leafminers may have invaded your garden. Spray at the first sign of infestation.

Slugs. Slug damage is characterized by large, rough-edged holes in stems and leaves. Also, slugs leave behind a slimy trail of silvery circles and irregular lines wherever they go. If you see signs of infestation, control with an iron phosphate slug and snail bait.

Leaf spot, crown rot, powdery mildw and other fungal diseases. These problems are usually signaled by a powdery residue on buds or flower petals, or by brown or black spots on the leaves of plants. In extreme cases, a general wilting of the entire plant from the bottom up may occur. To help keep your mums disease-free, take the following precautions:

• Avoid planting mums in poorly draining clay soils or on ground that that is frequently soggy or marshy.
• Mound your flower bed (or the soil around an individual plant) so that water runs away from the base of the plants.
• Water with a drip hose rather than an overhead sprinkler, especially in fall as the days shorten and the weather cools. Also, avoid nighttime watering.
• Divide any mums that have grown too large or have ceased to bloom as well as they once did. Plant your divisions in fresh soil that has not played host to mums before.
• Treat plants with a fungicide according to label instruction.  

Propagation

Mums can be propagated by seeds, softwood cuttings or division.  A great time to take cuttings is when pinching the plants back. You should divide mums every 3-5 years to promote overall plant health, foster better blooms and control plant size. Lackluster blooming of mums that have been well cared for is sure sign that your plants need to be divided, as is woody growth at the center. When dividing mums, pull divisions from the edges of the clump and discard (or compost) the woody center.

More about Mums

Plant Characteristics. Mums, like roses, have been relentlessly cross-bred for centuries, resulting in a profusion of hybrids, which can prove awfully confusing to the weekend gardener. Fortunately, a working knowledge of the key characteristics of mums can help you cut through the clutter and choose a plant that's right for you.

Size. Although mums as a group range in mature height from as short as six inches to as tall as five feet, most cultivars fall into the one to three-foot range (with a spread of 1 to 1.5 feet). The low-growing types are well-suited for potting, edging and rock gardens, while the taller types make beautiful specimen plants, especially when trained and pruned by an expert. Medium-sized mums, for their part, are wonderful just about anyplace you put them- in borders, in flower beds, in large containers, or as foundation plantings for evergreens.

Growing Habit. Nearly all hardy garden mums display a shrubby, mounding growing habit, particularly if pinched back in summer to encourage fuller growth and fall blooming. While other kinds (e.g. taller types, trailing types) are available, they are far less prevalent than the bushy varieties.

Foliage. Mums are noted for their finely textured, deep green foliage, which has a musky, aromatic scent and provides a rich, dramatic backdrop for the plant's flowers.

Hardiness. Generally speaking, mums are tolerant of light frost and can be reliably grown for late summer and fall blooms in nearly any temperate region. Here in the United States, that roughly translates to USDA Plant Hardiness Zones 4-8, though some of the newer hybrids exhibit improved winter hardiness and can thus be grown further north than older types.

Flower Color. Although the basic flower colors for mums are white, yellow, pink, red, orange, bronze, purple and lavender, mums are available in virtually any color imaginable.

Flower Form. The National Chrysanthemum Society (or NCS) has established a system of numbered classes to help gardeners distinguish between the flower forms most often seen in mums. There are twelve such classes in all, with a broad spectrum of color variation within each class.

Class 1: Irregular Incurve

Class 2: Reflex

Class 3: Regular Incurve

Class 4: Decorative

Class 5: Intermediate Incurve

Class 6: Pompom

Class 7: Single (or Daisy) and Semidouble*

Class 8: Anemone

Class 9: Spoon

Class 10: Quill

Class 11: Spider

Class 12: Brush & Thistle