My hydrangeas are blooming different colors?
Limestone is commonly used to raise pH and elemental sulfur is one way to lower soil pH. Your soil test will indicate the pH and provide recommendations, if necessary, for how much lime or sulfur is needed to bring the soil into the desired pH range for the plants. Just remember …. altering pH takes time.
To RAISE pH:
Apply dolomitic or calcitic limestone and mix it thoroughly into the upper 6” of soil. Dolomitic limestone contains magnesium; calcitic limestone does not. If you soil tests high for magnesium, choose calcitic limestone so as not to raise the magnesium level even more. The amount to add will depend on the buffer pH and the intended pH level. Add the lime well in advance of planiting sensitive plants, if possible.
Wood ash can also be used to raise pH. It is more potent and works more quickly that limestone. Wood ash also contains potassium, phosphorus, calcium, magnesium and all the other trace elements. Be sure wood ash is from clean wood NOT coal or charcoal. Adding too much wood ash can cause extreme pH changes. Apply wood ash in the winter and apply no more than 2lb./100 sq feet every two to three years.
To LOWER pH:
Apply horticultural or elemental sulfur and mix it throughout into the upper 6” of soil. Horticultural or elemental sulfur can be obtained from some landscape suppliers, or sulfur supplements for animal feed can be obtained from feed suppliers.
Applies to Hydrangeas in particular:
Iron sulfate (“ironite”) or aluminum sulfate may be more effective than elemental sulfur in lowering pH.
To obtain soil test kits, contact your County Extension Service
The Soil Testing Laboratory is a part of Rutgers New Jersey Agricultural Experiment Station (NJAES). The Soil Testing Laboratory is a service unit that performs chemical and mechanical analyses of soils for the residents of New Jersey and for University research personnel. Soil testing kits may be purchased from your local county office of Rutgers New Jersey Agricultural Experiment Station (NJAES) Cooperative Extension. For more information go to:
http://njaes.rutgers.edu/soiltestinglab