Soil Improvement and the importance of pH

The pH is a reading of the relative acidity or alkalinity of your soil. The lower the number the more acidic the soil; the higher the number, the more alkaline the soil. The pH is important because rose roots cannot absorb nutrients from a soil that is too acidic or too alkaline. The desired PH for roses to thrive is between 6.5 and 6.9 which is slightly acidic.

There are two simple ways to test your soil, one is with a soil testing kit and the second is with a pH Meter. Both can be purchased at a good hardware store or garden centre. The important thing when testing soil is to get a truly representative sample. This can be achieved by taking samples from different parts of the garden bed at varying depths (i.e. 1cm ‐> 20cm).

The general rule is the soil along the coastal plain is acidic, however in specific areas  it  may be completely different for any number of reasons, so it is always important to test your soil.

If your soil is too acid (i.e. lower than pH 6.5) you can bring it up by using dolomite. The amount to be added will vary with the type of soil and the degree of acidity. Dolomite slowly dissolves in the growing medium over time, helping to counteract the acidifying effects that some fertilizers and/or irrigation water can have on the growing medium. Dolomite also supplies roses with calcium and magnesium that is good for healthy growth.

Should your soil be alkaline (greater than pH 7) you can lower it by adding agricultural sulphur that will decrease the PH by one point per 80 grams per square metre. It may take four to six weeks to fully react, and the amount of sulphur needed for sandy or clay soils will be different, so you need to know your soil. To ascertain the amount to be added to your soil it is suggested you read the instructions on the packet. Check your soil in six to eight weeks. It may take one or two treatments, or it may be an ongoing process. For a quick fix a solution of apple cider vinegar at 5ml/litre of water applied weekly has the desired effect of reducing alkalinity however the effect is only temporary.

The general consensus is the different types of rootstock that roses are budded on are affected by the pH.

Although not the final solution to growing good roses, having the pH correct is a foundation stone and arguably second only to an adequate supply of water.