How to test the pH of soil and prepare a garden bed for sowing and planting

Winter brassica bed
  • In our winter brassica bed we have collards which are still going strong – we just pick leaves off the plants when we need them. The Romanesco broccoli is hearting up nicely – it’s a good alternative to cauliflowers. We planted sprouting broccoli (as opposed to heading broccoli) in the bed too, but it went to seed before it produced anything. We put this down to winter starting late this year and temperatures being unseasonally warm. But we’ve left the seed heads flowering because they provide food for the bumblebees and honey bees. Seeded broccoli also gives off a gas in the soil which sterilises it and prevents weeds from germinating. Broccoli flowers can be added to salads as edible decoration. Our green cabbages are all eaten, but the slower-growing red cabbages are ready for the table now.
Lupin green manure crop
  • The lupin green manure crop has been in for about 3 months. It could be dug in now but as we don’t need this bed for a couple of months yet, we’ll leave the crop in for a little longer. You should dig a green manure crop in though no later than when around 10 per cent of the plants are flowering. If you leave it any later, the stems of the plants go woody and it takes that much longer to break down. It usually takes 3-4 weeks after you’ve dug in a crop until you can plant in the bed.
Preparing a garden bed for planting
  • There’s one bed in the OEG garden that we didn’t do anything with this winter. We have weeded it, but it’s now compacted and could possibly have become acidic from the rain.
  • In order to ascertain the soil’s acidity or alkalinity, we’ll first do a pH test. 7.5 is alkaline and 4.5 is very acidic. Neutral is 7.0. Instructions on how to conduct the test are in the kit or follow Rob.
  • It takes about 10 minutes for the test to work, so in the meantime we’ll use a fork to aerate the bed. We’re not turning it over, rather lifting the soil to give it some air. This way we don’t disturb the soil structure.
  • Our soil test has ended up at 7.0 or Neutral, so we’ll apply gypsum (also known as Clay Breaker). Gypsum adds calcium to soil which helps build strong cell walls in vegetables. We would also add gypsum if our results had been Alkaline. If the test had shown the soil to be Acidic, we would have added garden lime to the soil instead to balance its pH. Apply at the rate of 2 handfuls per square metre.
  • Next we add rock dust which helps our vegetables to become nutrient-dense. Rock dust is also high in phosphorus which is good for the root vegetables we intend sowing.
  • Then a couple of barrow loads of compost goes in. Rake it evenly over the bed. Compost returns all-important carbon to the soil which may be depleted of it after the winds and rain of winter. And finally we distribute a barrow load of well-rotted chicken manure. This adds primarily nitrogen to our garden bed.
  • Leave for a week or two before sowing or planting and it’ll be fizzing with microbial activity!


Camera: Tom Neunzerling
Editor: Thomas Asche