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GARDENING Know your soil – and feed it

Outdoor Living
Feed the soil that  feeds the plant


Organic growing
Hans Wieland


Soil fertility is the key to growing vegetables successfully. Good fertile soil will produce healthy and nutritious vegetables and soil fertility can be improved through the addition of farmyard manure and compost and by sowing ‘green manures’.

Soil types


Clay soil
Heavy and cold. Sticky when wet, hard when dry. Susceptible to compacting. Drains poorly, but rich in nutrients. Can be greatly improved through the addition of organic matter.

Silt soil
Between clay and sand, but behaves more like clay soil. Good water retention and less drainage problems. Fertile and respond well to addition of organic matter.

Sandy soil
Light and warm. Heats up quickly in the spring, but dries out quickly, as it is unable to retain water. Nutrients wash out easily. The addition of organic matter will greatly improve this soil.

Peat soils
Rich in organic matter, but may be infertile and acidic.

Loam soils
Ideal mixture of more than one type. The sandy elements give good drainage and aeration, and the clay and silt elements provide nutrients and water retention.
Improve your soil
Plants absorb carbon from the carbon dioxide in the air, but they rely on soil for all other nutrients. Their major requirements are nitrogen, phosphorus, potash (K), calcium, magnesium and sulphur and also trace elements like iron, zinc and silica.
The easiest way to improve your soil is by adding an adequate supply of compost and farmyard manure. Planting leguminous crops as part of your rotation will ensure a balanced supply of nutrients to your crop. You will also improve the soil structure and the quality of your soil.

Green manures

You can also grow green manures to dig into the soil. This will enrich it and improve soil fertility and structure. If even a small piece of ground looks like being vacant for a few weeks, it is worth sowing a green manure. Green manures can increase organic matter in the soil and also increase nitrogen levels. They protect the surface over winter, help suppress weeds and increase drought resistance. In some cases the flowers attract beneficial insects. 
Green manures fall into three categories: Fast-growing leafy crops, leguminous crops and Fibrous-rooted crops. Fast-growing leafy crops, including mustard, rape seed, fodder radish and Phacelia, quickly provide a leafy canopy to suppress weeds and give an almost immediate supply of bulky organic material when dug in.
Leguminous crops, including various types of clover, alfalfa, bitter blue lupin, winter field beans, field peas, winter tares and common vetch, have nodules on their roots which fix atmospheric nitrogen in the soil releasing it slowly for the crops that follow them. Winter-hardy legumes such as field beans, tares and crimson clover can be used for over-wintering.
Finally, fibrous-rooted crops develop dense fibrous root systems which improve soil structure.  When dug in they increase the organic matter in the soil. Grazing rye and Phacelia fall into this category.

How good  is your soil?
Find out with two simple tests

The finger test

Rub a hand full of moist soil between your  thumb and your fingers. If the soil sample is sticky and can be rolled into a ball it’s clay soil. If the sample is soapy and leaves fingers dirty it’s silty soil and if the sample feels gritty and will not stick together it is sandy soil. Soil samples that look very dark with a spongy feel that cannot be rolled into a ball are peaty soil.

The jam-jar test
Half-fill a jam jar with soil, add water until it is three quarters full. Add some vinegar, put the lid on and shake for one minute and put it down immediately. The various fractions of sand, silt and clay will separate, and an approximate proportion of each will show. Sand and stones at the bottom, then silt, then clay with organic matter floating or on top of the clay.

* Please do remember that the soil can vary considerably even in a small area so take a few samples.

Hans Wieland is joint manager of The Organic Centre, Rossinver, Co Leitrim, which offers courses, training and information in organic growing, and runs an Eco Shop and an online gardening store. For more information, visit www.theorganiccentre.ie, e-mail info@theorganiccentre.ie or phone 071 9854338. Questions or comments? Contact Hans at living@mayonews.ie.