When and How to Fertilize Mums for the Biggest Blooms

Chrysanthemums reliably mark the fall transition, providing a welcome flash of color among muted seasonal hues. They bloom profusion from early autumn through frost in jewel tones of deep reds and purples to bright golds, oranges, and pastel pinks. From a mounding blanket of blooms to showy cut flowers, different varieties bring intrigue to the display.

The infusion of color takes energy to produce, from setting buds to a lasting show. With nutritionally rich soils and light, well-timed feedings, the number and size of buds and blooms get a boost. With a limited, strategic application of organic amendments or fertilizers, your autumnal mums will bloom bold and bright.

Do All Mums Need Fertilizing?

Hardy garden mums benefit from organic, rich, humusy soils to thrive. With the right foundation, they don’t need fertilizer to flower but may have a looser form to accompany their profusion of blooms. The graceful, mounding habit is a lovely addition to border edges and along the tops of walls.

Fertilizer provides the benefits of supporting strong, bushy stems and an even greater number of blooms and more prominent mum flowers. With the right timing, additional nutrients prevent premature budding and flowering by promoting leafy growth before the bud stage. It boosts vigorous plants for fresh, green foliage and higher bud set. 

Commercial growers rely on fertilizer for those picture-perfect specimens we find in the fall. Fortunately, the applications are less intensive in the home garden, ranging from organic soil amendments to liquid feeds.

Types of Mum Fertilizer

Fertilizing chrysanthemums is a streamlined process, limited to a couple of times a season. The timing and method are important, as feeding is most valuable during the vegetative stage. Extra nutrients during this phase, especially nitrogen and potassium, support healthy leaf and root development. 

Before the mums go in the ground, amend soils with compost or organic material. Blood meal, bone meal, or greensand increase available nutrients. Choose your fertilizer and method regarding when and how to apply it.

Take care not to overfertilize. More is not better when it comes to applications. An excessive amount or improper application time leads to too much nitrogen. Excessive nitrogen promotes a quick overproduction of vegetative growth. The result is weak, leggy, languid branches. Fewer buds result as leafy growth takes the plant’s energy. Excessive salts left behind damage the roots. Following application guidelines and measurements prevents overfertilizing.

Timing the Applications

It’s best to feed mums before the bud stage and the high summer heat. A spring and summer application, depending on fertilizer type, is usually all that’s needed. If you don’t intend to keep your bloomer beyond this season, don’t bother fertilizing. Nursery-potted specimens come already fed and ready to flower and won’t benefit from the additional resources.

Aim for a balanced (or nearly so) NPK ratio (nitrogen-phosphorous-potassium). Nitrogen promotes leafy growth and stems, phosphorous stimulates roots and flowering, and potassium yields sturdy branches. Avoid an overly high phosphorous (P) number to prevent premature flowering when buds emerge too early in the season.

Controlled release tends to last for a few months, releasing more during warm temperatures (above 70°F or 21°C) and with rain and irrigation. Slow release holds for an entire season, releasing variably. Liquid feeds absorb quickly into tissue and roots and require a more frequent, once-monthly application.

When to Start And Stop

When to add nutrition depends on the plant stage you’re starting with. Begin with a well-balanced fertilizer at planting for in-ground and container mums. For newly transplanted divisions or if installing a nursery-potted grower, wait a few weeks to apply a balanced formula.

Young, tender transplants need time to establish roots, and display-ready nursery pots are usually fertilized prior to sale and flowering. For established perennials, start a regimen in spring after frost passes. Wait until new growth emerges and reaches four to six inches tall.

Stop fertilizing when buds begin to develop in early to mid-summer. This is when the plants need to direct energy into flowering rather than producing leafy growth. Halting fertilizer also protects from encouraging stressful overgrowth during periods of intense heat, when growth naturally slows. Some gardeners opt to use a high-phosphorous fertilizer in the fall to promote root growth before overwintering (without hampering flowering).

Applying the Nutrients

Early in the day is the best time to apply fertilizer, out of the sun’s direct afternoon rays. Even better if you have overcast conditions, which help prevent foliar burn. Rinse leaves and stems and water roots immediately after granular applications to get rid of dust and prevent direct contact. 

If planting a larger area or mixed arrangement in poor soils, use a “bulk” method by applying one to one-and-a-half pounds per 100 square feet and working it into the soil.

When using granulars, spread them evenly around the base of the plant, keeping grains away from the stems. Uniform spreading helps to avoid hot spots and prevent burn damage.

Water-soluble and liquids work as foliar feeds and root drenches. Spray the foliage and root zone to distribute the nutrients. Plants absorb and utilize liquid feeds quickly, so they’re applied more often than granules.

Other Soil Considerations

Establishing healthy foundations with organically rich, loamy soils and good drainage is the best situation for chrysanthemums, which will be less fertilizer-reliant. Soil pH is also helpful to know for growing ornamentals. Like most garden selections, mums prefer neutral to slightly acidic soils with a pH between 6.5 and 7.0. If your mums show signs of yellowing despite fertilizing (first, make sure watering issues or pests aren’t the problem), there may be a pH imbalance.

Fall is an ideal time for a soil test, which is also the best way to determine pH. At-home kits that interpret the results and offer recommendations help assess the soil’s conditions and what needs improving. Your local university extension office is another resource for tests and recommendations.

When it comes to soil pH, beneficial microorganisms do their best work in neutral to slightly acidic soils. An off-kilter acidity or alkalinity level impacts the roots’ ability to access and absorb nutrients. Beneficial microbes have difficulty breaking down organic matter to nourish roots.