managing soil ph levels

Managing soil ph levels in your organic garden

Managing soil ph levels in your vegetable garden can make a big contribution to its success. There are a number of ways to easily and quickly fine tune your soil ph levels.

How is ph measured?

Soil acidity is measured by a ph test. Ph test kits can be bought inexpensively at most nurseries and they are very easy to use with instructions provided. I use one that has a colour range and you put some powder and liquid from the kit on a sample of your soil and compare this to the colour range which has the ph number against the colour tone. If your soil ph is below 6, then it is said to be more acidic (sour) and if it is above 7, then it is more alkaline (sweet). So the ideal range for growing vegetables is from 6-7 ph.

Impact of ph levels

When your soil ph is out of the ideal range, the essential minerals and nutrients in the soil are largely unavailable to your plants. This will result in stunted plants, yellowing leaves, poor root and leaf growth, lack of flowering/fruiting and much higher propensity for the plants to be subject to pests and diseases. All in all, not happy plants.

How to manage quickly

In managing soil ph levels, the easiest way to increase the ph into an ideal range, if its acidic, is to apply garden lime (make sure you avoid builders lime which is used for concreting). Dolomite is garden lime mixed with magnesium and this provides extra benefits for plant growth. Here is a table of application rates based on soil texture:

Soil texture Garden lime Dolomite
Sandy 120gms m2 110gms m2
Loam 320gms m2 300gms m2
Clay 440gms m2 360gms m2

Spread the lime or dolomite over your bed, lightly dig it into the soil to about a garden fork depth and then water it. The affect on ph will take about 2-3 weeks, however it would be OK to plant out your beds straight after application. Wear a dust mask when applying the lime.

If your beds are alkaline (over 7 ph), you need to bring them back to between 6-7 with the optimum at 6.5. Powdered sulphur can be used for this with application rates shown below. You can also use pine needle and oak leaf mulch.

Soil texture Powdered sulphur
Sandy 50gms m2
Loam 75gms m2
Clay 96gms m2

The best time to apply these amendments to your soil are:

  1. When you start the garden or have revived it after a period of neglect
  2. After an extreme weather event with flooding as this will make your soil more acidic
  3. Each year when you prepare your beds for the year’s cropping

You may have used gypsum in your organic garden in the past. This is lime and sulphur and it has a neutral effect on soil ph because lime makes it go up and sulphur makes it go down. So don’t use gypsum in managing soil ph levels. Its a great product to use in giving the soil sulphur which is a vital ingredient in the soil, as is lime (calcium).

Experiment with your crops

As part of your learning process in managing soil ph levels, I also suggest experimenting with growing vegetables, herbs and fruits that grow OK outside of the ideal ph range:

The medium term solution – organic gardening and biodynamic methods

In managing your soil ph, the most sustainable medium term solution is to incorporate compost, green manure, crop rotation and soil additives to stimulate healthy soil life. These are all proper organic growing processes that contribute to building soil humus and it is the life in the humus that mediates the ph to the ideal level. I also use biodynamic preparation such as BD500 and BD cow pat pit to improve humus levels. I recommend doing one ph level test each year for the first 3 years of your food garden.

We help you to understand and apply managing soil ph levels, supported by organic and biodynamic methods in our workshops and through our mentoring service.

Happy gardening

Authored by Peter Kearney – www.myfoodgarden.com.au

Posted in biodynamic gardening, Mentoring, urban agriculture, urban farming, vegetable gardening and tagged , , , , .

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