Foxgloves (Digitalis purpurea) are beautiful and elegant. Their tall, curving racemes of pink and purple blooms are indispensable in the cottage- or English-style garden. Usually easy to grow, foxglove does need a few basic conditions to thrive. One of the easiest conditions to modify is soil acidity. Attention to soil acidity will go a long way toward achieving beautiful foxgloves.
Foxgloves grow best in neutral soil--about 6.50 pH. Soils that are too acidic or alkaline will result in poor nutrient uptake. Even though nutrients may be present in the soil, they are not available to plant roots if soil pH is off.
Soil for foxgloves should be moist, well-drained and rich in organic matter. It should contain adequate amounts of macronutrients (nitrogen, phosphorus and potassium) as well as micronutrients (iron, magnesium and manganese, for example). Rich, loose soil not only ensures proper drainage, but also adequate aeration.
The primary symptom of poor pH in foxglove is chlorosis. Chlorosis, or leaf yellowing, usually occurs because of nutrient deficiency. Chlorotic leaves lack chlorophyll, making them unable to convert sunlight into plant energy. Iron, nitrogen and magnesium deficiencies are common causes of chlorosis. Foxgloves suffering from chlorosis eventually lose their leaves and die if left untreated.
Amend soil with compost or well-rotted manure--about one-third--to improve drainage and nutrient uptake. Amend heavy soils with an equal amount of compost and sand. Sand also moderates acidity in acidic soils, while compost and rotted manure moderate alkaline soils. In highly alkaline or acidic soils, lower pH by adding aluminum sulfate or iron sulfate and raise pH by adding lime. A soil analysis will confirm the specific pH and nutrient needs of garden soils.
Remove dying and dead leaves from plants throughout the season and in the fall when plants go dormant. Not only will this help prevent fungal diseases, it keeps organic matter from building up, which can increase acidity. Fertilize as needed with perennial flower fertilizer according to label directions. Add amendments to adjust soil pH when a soil test indicates it is needed.