Gardening Wisdom

Plant Care: Mums in the Garden

October 21st, 2008

Garden Mums will prosper in full sun to partial shade and prefer well-drained soils amended with organic matter. In sandy soils, a 3 to 4 inch layer of peat or compost should be worked into the top six inches of the soil. From late spring through mid-August, lightly prune stems without flower buds when they grow over six inches by snipping off the top 2 inches of growth. Prune off dead flower spikes. Some varieties of Garden Mum produce tall flower spikes which must be staked.

Planting Location

Chrysanthemums require well-drained soil and full sunlight to grow and successfully bloom. This means generally 6 hours of sunlight or more each day during the summer period. Plants grown with less light will become weak, spindly and produce few flowers. Avoid locations which are exposed to street or porch lights as this will interfere with the flowering light response to shortened days. The best location is a southern or southeastern exposure preferably against a foundation or wall where additional protection is given from frost. Improve the drainage before planting by elevating the bed with a good mix of garden loam and compost.

Soil Preparation and Planting

Garden soil which is good for growing vegetables will be satisfactory for growing mums. If particularly high in clay, additions of organic matter including peat, composted leaves, rotted manure or straw will improve the drainage and aeration. While working the planting bed, collect enough soil for a soil test and follow the recommendation for amounts of fertilizer to be added. Containerized plants should be planted at the same depth at which they were grown. Do not bury the root ball. This will promote a lack of root aeration and root rot caused by fungal pathogens. Chrysanthemums are shallow rooted and do best if planted high. This means that frequent watering may be necessary during times of high heat and little rainfall. Space plants generally about 18 inches apart. Spreading varieties may require larger spacing.

Pinching

To generate a plant full of flowers and control growth, chrysanthemums require some pinching of the tips. This encourages branching and more compact growth. It also will stimulate more flowers to be produced. Pinching is done by removal of about an inch of the tip of each branch or shoot. This is snapped out with the thumb and index finger. The first pinch should be done when the plant is 6 to 8 inches tall and repeated when new branches become 6 inches tall. A third pinch may be necessary on fast-growing varieties. If plant are not properly pinched, they will become tall, leggy, easily blown over by winds and have few flowers.

The most important thing to keep in mind when pinching the growth back is the timing of the last pinch. For early flowering varieties which bloom in mid-September, the last pinch should be around the middle of June. Varieties which flower in the early part of October should be given a last pinch on July 1. Later flowering varieties should be pinched for the last time no later than July 15. Overall, about 3 months is required between the last pinch and bloom. This is a general rule which can guide you in controlling the growth and stimulating more bloom production.

Fertilization

Most mums will require fertilization several times during the spring and summer to stimulate good growth, produce thick stems and maintain a healthy green color. Chrysanthemums are not heavy feeders like vegetables so, it is best to use a dilute fertilizer applied several times prior to bud set. Nitrogen has the greatest effect on flower production and general growth. If too much is applied, vegetative growth will be hard to control, fewer flowers will be produced and overall, flowering will occur later in the season. Before planting a bed in the spring, about 4 pounds of 5-10-5 per 100 square feet can be worked into the soil to a depth of 6 inches. This gives about one-quarter pound of nitrogen per 100 square feet and should be enough fertilizer for the season if abundant organic matter is present. A second application around August 1 may be beneficial especially on poorer soils.

Apply about 2 tablespoons of 10-6-4 or 4 tablespoons of 5-10-5 fertilizer spread over a 2 foot circle at the base of individual plants. Alternatively, broadcast about 2 pounds of 5-10-5 per 100 square feet. No more than about a tenth of a pound of nitrogen should be applied at this time.

General Care and Maintenance

During the early part of the summer, a layer of mulch material should be applied to the soil after it has warmed up as this has definite advantages to conserving and regulating moisture to these shallow-rooted plants. Besides the benefits of water control, mulch protects the bed from erosion, compaction and retards weed seed germination. Use a 2 to 3-inch layer of coarse peat, leaf mold, compost, nut hulls or lawn clippings mixed with leaves. Mulches composed of chipped wood, sawdust and straw may consume nitrogen fertilizer and rob the root system. If you use these materials as mulch, double the fertilizer applied to the bed.

If you cannot control the growth of the plants to the point that they have become tall and begin to drop over, then some support may be necessary in the form of wire frames or upright stakes. Wire peony or tomato frames work well and should be put in place before they are needed, otherwise these will be more difficult to position without damaging the plant.

After the plants have flowered, the stems should be cut off close to the ground. Leaf, flower and stem debris should be collected and composted provided they are not disease or insect infested. If that is the case, the materials should be composted separately and not used for mulching or soil improvement around the plants. Disease or insect infested materials can be buried and left out of the garden.

Often chrysanthemums listed in catalogs are noted as being winter hardy meaning that the plants will overwinter and grow the following season. The term “hardy” has been used sometimes inappropriately and gardeners should be cautious about believing that all mums are winter hardy when stated so. The fact is that many mums are not reliably hardy depending upon the climate conditions presented and even the most hardy varieties may not make it through a severe winter of subzero temperatures.

Many mum selections will survive the winter if the plants gradually become frozen and remain that way until spring. Deep snow cover will assist this and protect the frozen soil if it remains intact throughout the winter. The best defense against adverse weather conditions is to provide good drainage so that water does not accumulate around the plants and promote ice formation. After the first frost, mound a few shovels of soil forming an 8-inch layer around the base of each plant. Cut the branches back to 10 inches above the soil line and apply a 2 to 4-inch mulch layer as soon as the soil surface freezes. This means loosely layering evergreen branches, straw, or other lofty materials around the plants. Avoid using materials like leaves or peat moss which will pack down and retard emergence of leafy shoots in the spring. After the last danger of frost has past, this mulch and soil can be removed. If leafy growth has already started and the possibility of frost is still present, apply another layer of loose mulch to protect the growth.

As an alternative to overwintering plants in the bed, they can be dug and placed into cold frames to better ensure survival. This means a little more work, but for those varieties which are more tender, it is often the only way to keep plants from one year to another.

• Mums in the Garden (PDF)