Chrysanthemums (mums) are celebrated for their vibrant autumn displays, but spectacular fall blooms depend entirely on the care they receive during the summer months. Summer is the vegetative growth phase where these plants focus on building a strong, bushy framework to support dozens of flowers later in the year. The health and size established from June through August directly determines the quantity and quality of the flowers that will emerge as the days shorten. Successful summer management prepares the plant for its seasonal finale, rather than encouraging early flowering.
Managing Hydration and Heat Stress
Mums possess a relatively shallow root system, making consistent soil moisture a daily concern, especially during peak summer temperatures. The goal is to keep the soil evenly moist without becoming waterlogged, as poor drainage quickly leads to root rot. During periods of intense heat or drought, checking the soil moisture one or two times a day may be necessary to prevent wilting and heat stress.
When watering, apply water directly to the base of the plant to ensure deep saturation of the root zone, avoiding overhead spraying. Wet foliage, especially overnight, creates an ideal environment for fungal diseases like powdery mildew. A layer of organic mulch, approximately two to three inches deep, is beneficial, as it insulates the roots from scorching temperatures and reduces water evaporation.
Chrysanthemums thrive with six or more hours of direct sunlight daily, but intense afternoon sun in the hottest climates can cause leaf scorch and heat stress. In regions where daytime temperatures regularly exceed 75°F, position plants to receive bright morning sun followed by afternoon shade to mitigate heat effects. Consistent hydration and strategic placement are the primary defenses against summer setback, ensuring the foliage remains healthy and active.
Essential Summer Pinching for Fall Blooms
Pinching is a mandatory technique for garden mums, redirecting the plant’s energy to produce a dense, rounded shape capable of bearing a heavy floral load. This process involves manually removing the top half-inch to one inch of new stem growth, typically using the thumb and forefinger. Removing the apical meristem, or the main growth tip, temporarily breaks the plant’s apical dominance, which causes a single stem to grow tall and straight.
Breaking this dominance forces the plant to activate dormant lateral buds along the stem, resulting in multiple side branches. Each new side branch becomes a potential stem for a cluster of fall flowers, transforming a single-stemmed plant into a full, bushy mound. The first pinch should occur when the plant reaches about six to eight inches in height in late spring.
Subsequent pinching should be repeated every four to six weeks, or whenever new growth reaches six inches long. This consistent pruning must stop by mid-July in most regions, or early August in cooler climates. The plant needs time to set its final buds for the fall bloom, requiring a period of unpruned growth for buds to form in response to shortening day length. Pinching past this cutoff date can delay or significantly reduce the number of flowers produced.
Maintaining Vigorous Growth and Health
Chrysanthemums are considered “heavy feeders” during their summer growth phase, requiring a steady supply of nutrients to support the rapid development of stems and foliage. A balanced, water-soluble fertilizer, such as a 10-10-10 or a formulation slightly higher in nitrogen, should be applied every four to six weeks from spring until early August. This regular feeding supports the vigorous vegetative growth necessary for a dense plant structure.
Cease all fertilization by August 1st, or as soon as flower buds begin to visibly set. Continuing to apply nitrogen-rich fertilizer once buds are forming encourages the plant to produce more leaves instead of flowers, potentially delaying or preventing blooming. A shift to a fertilizer with higher phosphorus and potassium may be beneficial during the final weeks before bud set to promote strong flower development.
While mums are relatively resilient, summer humidity can encourage common problems like powdery mildew, which appears as a white, dusty growth on the leaves. Ensuring plants are spaced 18 to 30 inches apart provides good air circulation, which is the best preventative measure against fungal issues. Pests such as aphids and spider mites can also emerge, but these are typically managed with targeted applications of insecticidal soap or neem oil if infestations become noticeable.