Acidic soils can cause nutritional problems for many plants, including a plant's inability to absorb phosphorous, nitrogen and potassium. However, many species tolerate or even require mildly acidic conditions to grow well. Roses do well in a slight-to-moderate acid soil, but even these acid-loving plants can't tolerate high acidic locations.
Abundant rain often creates acidic soil conditions, because rainwater itself is slightly acid. Other factors that encourage acidic soil include heavy local forest cover or large amounts of decaying organic matter, such as compost. Acid soils can increase the risk of some plant problems, such as slow growth or dead tissue at the edges of leaves. Roses grown in highly acid soils may have yellowed, spotty leaves. They also suffer from zinc, manganese, iron and aluminum toxicity and show reduced flowering.
Rose Soil Preferences
Roses grow best in slightly acid soil, with a pH of 6.5 to 6.8. This allows for the best uptake of major nutrients. However, many varieties will still grow well in soils as acid as pH 5.5. Excessively alkaline soils can cause manganese and iron deficiencies.
In areas where the soil pH is too low, or acidic, add alkaline soil amendments to create conditions where roses grow successfully. Raise soil pH by adding ground limestone directly to the surface of the soil around the plant. You can also mix agricultural lime or wood ash into the soil around your roses. These materials are more alkaline and can cause "burn" damage to rosebushes if applied too heavily. Apply these soil amendments only every other year.
Excessively alkaline soils, such as those found in prairie areas and arid regions, or in areas where the soil contains large amounts of natural limestone, may need acidic soil amendments for roses to thrive. Add shredded leaves, sawdust, peat or pine needles to your soil before planting. This decaying organic material will decrease the pH of the soil. Organic material takes time to work, however. Apply sulfur soil additives around existing rosebushes for a more significant effect.