Getting your pH right!

The first step to getting the pH ( figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acid, and higher values more alkaline) of your soil right, is to measure the soil’s pH. This is as simple of making a50/50 mixture of soil and deionised water, waiting 5 minutes and then dipping a pH strip into the mixture. These inexpensive strips are available from Plant Health Solutions in a form that measures finer graduations than normal. You are seeking a pH of 6.4 for optimal plant health growth. It is always important to try to understand why your soil is acidic or alkaline.

The best option is a soil test so there is no guess work involved. If you have acreage, a soil test can be worth its weight in gold. It is common to waste huge amounts of precious time, driving blind in an acreage gardening project, when a soil test would immediately clarify options and strategies.

If you can’t justify a soil test then these guidelines may assist you to diagnose the source of your pH imbalance:

If you have a light, sandy soil that is acidic, then you probably need a mixture of calcium and magnesium (dolomite) to correct the imbalance.

If it is heavier soil with more clay component then you probably need limestone to alkalise the soil and you might choose to include some gypsum to help break up the clay. If the soil is heavy and alkaline, then there is probably too much magnesium and sodium, so gypsum is the correction of choice.

Selecting compost and manures

Manures and composts come in may forms. In choosing to use any of them you should consider what you aim to achieve.

Mushroom compost has great levels of carbon and is terrific for building soil profile while not having an impact on nutrient levels.

Animal manures will have differing mineral analyses depending upon the source. Chicken (chook) manure contains good levels of phosphorous, while cow manure contains a greater overall mineralisation. All animal manures are a good source of the important minerals, nitrogen, potassium and phosphorous, and chook manure is also a good source of calcium.

All animal manures need to be used sensibly to avoid imbalance and nutrient run-off into the surrounding environment.  We need to strike a balance in garden inputs as an oversupply of nitrogen via manures can risk unhealthy nitrate contamination of our vegetables.

If manures are composted or purchased in a composted form then there is no risk of leaching or oversupplying nitrates because the nitrogen has been complexed and stabilised. Composting can increase the availability of the nutrients, introduce effective soil microbes and break down carbon into humus making it more effective in terms of water and mineral retention in the soil. Overuse of uncomposted material can lead to serious mineral imbalances and lock-up trace elements.

There is also the potential issue of weed seed contamination. Nitrogen in fresh manures is volatile and easily escapes into the atmosphere. Incorporating into a compost pile or digging the manure into the soil can help slow down this mineral loss.

Chook (chicken) manure is considered ‘hot’ when fresh. This means it is likely to burn delicate and sensitive plant roots and some soil microbes. It is a good strategy to compost this manure if that is possible. This manure has a fairly low carbon content unless it contains sawdust or straw.

Mushroom compost has a high carbon content but it is generally low in overall nutrient content. The pH of mushroom compost can range from 6.8 to 8. Preferably select a product with a pH below 7.

Cow manure and products made from cow manure have good levels of carbon and nitrogen but usually contains weed seeds as well.

Horse manure has great levels of carbon and breaks down quickly. Compost worms love horse manure but care needs to be taken to avoid manure straight after the animal has been wormed o vaccinated if it is to be used to feed worms. Once again there will the issue of weed seeds.

Green manure can be grown during the off-season or when resting beds in a rotation. Green manure crops build humus levels while feeding your beneficial soil microbes and earthworms. In warm areas try oats, Japanese millet, buckwheat, mung bean. In cooler areas, fava beans or fenugreek can be used.