Chrysanthemums (mums) are popular garden additions, celebrated for their vibrant autumn blooms. Their success is heavily influenced by the soil’s pH level. Understanding the specific soil preferences of the chrysanthemum is the first step in cultivating robust and healthy plants. The soil’s acidity or alkalinity directly affects how the plant can absorb necessary nutrients, making pH management fundamental.
The Preferred Soil Environment for Mums
Mums do not prefer highly acidic soil, despite the common misconception that many garden flowers do. These plants thrive best in soil that is slightly acidic to neutral, with an ideal pH range generally falling between 6.0 and 7.0. Within this bracket, some sources suggest a slightly more acidic range between 5.8 and 6.2 for optimal growth of garden mums. This range ensures the best environment for root function and nutrient uptake, preventing common deficiency issues.
A pH below 5.5 is considered too acidic for chrysanthemums, which can lead to problems with nutrient availability. Conversely, a highly alkaline soil, with a pH above 7.5, also presents significant challenges for mum cultivation. While they are relatively tolerant compared to truly acid-loving plants, moving too far outside the sweet spot will negatively impact their growth. Maintaining a well-drained soil structure rich in organic matter is equally important for overall plant health.
How Soil pH Impacts Chrysanthemum Health
The soil pH is a measure of the hydrogen ion concentration, and it critically determines the chemical form and solubility of nutrients. This is why pH matters more than simply the presence of nutrients in the soil. When the pH is too high (alkaline), essential micronutrients, such as iron (Fe), manganese (Mn), and zinc (Zn), become less soluble and are “locked up” in the soil.
This nutrient unavailability often results in a condition known as chlorosis, where the leaves turn yellow while the veins remain green. For mums, high substrate pH above 6.5 is specifically known to inhibit iron uptake, causing this interveinal yellowing on newly developed leaves. Extremely low pH, typically below 5.5, can increase the solubility of elements like aluminum and manganese to toxic levels. Aluminum toxicity can severely damage root growth and function, which further hinders the plant’s ability to absorb water and nutrients.
Practical Steps for Adjusting Soil Acidity
Before attempting any soil adjustments, first determine the current pH level using a home soil test kit or by sending a sample to a professional lab. A laboratory test provides the most accurate results and often includes recommendations for the amount of amendment needed. The results of the test will guide the quantity of material required, as the soil type, such as sandy or clay, significantly affects the buffering capacity and the amount of amendment needed to change the pH.
If the soil test indicates a pH that is too high (alkaline), you need to lower the pH and increase acidity. The most common and effective material for this purpose is elemental sulfur, which soil bacteria convert into sulfuric acid over time. This conversion process is slow, meaning that elemental sulfur should be applied at least six months before planting for the best results. Incorporating Canadian sphagnum peat moss into the soil can also help reduce the pH, as its natural acidity is typically between 3.0 and 4.5.
Conversely, if the soil is too acidic and the pH needs to be raised toward the neutral range, a liming material is necessary. Agricultural lime is the standard amendment for raising pH, usually either calcitic lime (calcium carbonate) or dolomitic lime (calcium and magnesium carbonate). Dolomitic lime is often favored because it also supplies magnesium, a nutrient frequently required by chrysanthemums.
Lime should be applied gradually and incorporated into the top six to eight inches of soil, as it is not water-soluble and moves slowly through the soil profile. Wood ash, a byproduct of burning wood, can also be used to raise pH due to its high content of calcium and potassium, but it should be used carefully due to its variable composition. Both sulfur and lime are best applied before planting, as incorporating them deeply into the root zone is difficult once the mums are established.