How to use a soil-testing kit

Testing your soil for acidity and nutrients will encourage healthier growth, says Tim

Tim Rumball

IF you want plants to grow you have to give them the right food, and the right conditions for them to make use of it. The acidity or alkalinity (pH) of garden soil affects the way food can be taken out of the soil by plants, but the essential nutrients – nitrogen, phosphorous and potassium (NPK) – must be there in the first place. So it’s important to know not just the pH, but also what’s missing so you can add more, and what’s already there so you don’t provide too much!

Simple testing kits that just determine soil pH are widely available. You can also buy more elaborate kits from garden centres and online to determine NPK, but for both types the starting point is a good soil sample.

How to take a sample

Take soil samples in dry weather when it hasn’t been raining for at least a couple of days. Don’t take samples if you have added lime or humus-rich material to the soil within three months.

From a garden flowerbed take three separate samples from different points across the bed. Cleanliness is essential. Wash, rinse, then dry your garden trowel and use it to scrape away the top 2in (5cm) of soil at each sampling point.