How To Use Tools: get the best out

Best techniques to get the job right with Tim Rumball How to use tools

How to use a soil-testing kit

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

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.

It is worth taking the time to understand your soil –it is the key to better results Add garden lime to make soil more alkaline. It is frequently used on vegetable beds and it is considered organic

Tim

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. Take a spit of soil, about one-third of the trowel blade, from the base of the hole and put it in a clean container. Take your other two samples in the same way and mix all three together, removing stones and larger debris. Spread the soil out in a tray under cover and leave it to dry naturally for 24 hours. This soil sample can be used for all four tests.

How to process the sample There are many soil-acidity test kits available. They all work on the same principle but they do vary, so follow the instructions provided. For the one I’m using, soil from the dry sample is put in the test tube up to the 1ml mark, a measure of barium sulphate and then water (use distilled, available from chemists) is added and shaken vigorously. It’s left to settle, then the top liquid is siphoned off and put in a separate tube with a couple of drops of pH test solution. Compare the colour of it against a chart. Dark green shows neutral soil, pale green to blue is alkaline, and varying shades of yellow to red indicate an acid or very acid soil. To test for NPK you’ll find a kit similar to mine at  crocus.co.uk. For nitrogen my test kit uses a filter to extract nutrients, but not all do. Again, follow the instructions in your kit. I put 1ml of dry soil in the filter with 2½ml of N1 test solution and press the solution through the filter.

How to read the sample The resulting liquid is put in a clean test tube with a measure of N2 testing powder, covered, shaken and left to stand for five minutes. The colour of the liquid in the tube is then compared to the nitrate reading chart. A rich-purple colour means the soil has lots of nitrogen, while pale-lavender means it’s low in nitrogen. The same procedure is followed when testing for potassium and phosphorus, but using the relevant testing solutions provided in the kit.

How to redress the deficiencies Comparing the colour of a tested soil sample with the appropriate colour chart is not always clear. A bit of interpretation

Testing for nitrogen, phosphorus and potassium

is often necessary, but the tests give an indication of acidity or nutrient levels. If your soil is acidic (below pH7) and you want to grow plants that need neutral or alkaline soil, you can rake in a light dressing of garden lime. If your soil is alkaline (above pH7) and you want to grow acid-loving plants, then sulphur chips, or sulphate of iron will help. If your soil is lacking in nitrogen, which promotes leafy growth, dig in well-rotted manure or mulch the soil with it. You could also use the chemical ammonium sulphate, which is very strong so should only be used as clearly directed on the product packaging. For a deficiency in phosphorus, which promotes healthy root growth, soft rock phosphate can be used, or bonemeal (not blood, fish and bone, which is a balanced fertiliser). Both are organic products. Low levels of potassium (potash), which boosts flowering and fruiting, can be corrected with an application of the chemical sulphate of potash. Use as directed on the product packaging to correct the balance. For an organic solution use seaweed meal, or spray plants or water on a solution of seaweed liquid fertiliser.

Anatomy of testing soil fertility

1. Range of products to correct soil fertility.

Step by step

Testing the pH of soil

1Place the required measure of dry soil in a tube and add the required measure of barium sulphate (I made the stand for the tube out of an old plastic milk bottle).

2. Simple acidity (pH) soil-testing kit.

3. Full spectrum soil test kit for acidity as well as nitrogen, potassium and phosphorus.

4. Clean bowl and trowel to take soil samples.

Do’s and don’ts of soil testing

Do ✓ Take soil samples from several locations in a flowerbed, and mix them together so you get an average across the whole bed. ✓ Follow instructions very carefully –the tests are not difficult to do but the correct sequence must be followed. Don’t ✗ Use a test kit more than one year old as the chemicals can degrade and give false readings. ✗ Use dirty kit. Wash and dry the trowel and soil-collecting bowl before use, and wash and dry the test kit between tests.

Take soil samples from several locations

Follow instructions carefully

2Add distilled water to the level indicated, put on the cap, shake and then leave it to settle. Draw off a measure of the liquid in the top layer using the pipette supplied.

3Squirt the sample into the small tube supplied, add two drops of the pH reagent, then close the cap securely and give it a good shake. The colour will change.