Soil Preparation

by | Apr 6, 2017 | Gardening, Grow Your Own, Herbs & Vegetables | 3 comments

Laying The Foundation

Proper soil preparation is the foundation on which a productive food garden is built so it’s important not to skip this step, whether you are working with virgin soil or previously used beds.
It is hard work and if the soil has not been worked before, it could take half a day to a day to prepare the beds for a 9 m² area. Double digging the beds loosens and aerates the soil. Dig to a depth of 60cm and incorporate 10 litres of compost (about a bucket full) per square metre.

The aim is to have friable soil that drains well and also allows the roots of the vegetables to draw up the oxygen and water. The ideal soil structure is 50% space (water and air) and 50% minerals.

This method of double digging does not move subsoil to the top or vice versa. There is no displacement of the aerobic micro-organisms that exist in the top 30cm of soil or the anaerobic organisms in the lower level that does not need oxygen to function.

A bed that has been prepared in this way will not need to be dug again like this for the next four to five years. When planting a new crop it just needs to be topped up with compost and topsoil which is lightly forked in.

Double Digging Step-By-Step

Step one: Water the area two days in advance, then measure and mark out the beds using sticks and twine.

Step two: Dig the bed in sections, about 1m² at a time. Remove the top 30cm of soil, about the depth of a spade tine, and put it to one side.

Step three: Using a fork loosen the second layer of soil to a depth of 30cm but do not remove the soil. Fork in compost. One bucket of compost (10 litres) is used per 1m² for enriching both the topsoil and subsoil.

Step four: Dig the next 1m² section but do not put the top soil to one side. That top soil (mixed with compost) is turned into the first section.

Step five: Follow this process of turning the topsoil from one section into the previous section until you reach the end of the bed. At the end of the bed, you will take the top soil from the first section and mix it into the last section. Digging the bed in sections and completing each section is actually more time and labour saving than digging all the soil out, mixing it with compost and returning the soil. It also allows you to complete the job in phases.

Step six: You will find that with the addition of the compost and the aeration of the soil, the level of the bed will be about 15cm higher than the surrounding soil. Skim off the top soil from the pathway and add it to the bed. This further raises the bed.

Step seven: Rake the bed to level it. Any clumps of soil, roots etc, can be raked into the pathway but rocks and stones should be removed.

Step eight: Rake the soil so that it is worked to a fine tilth, because in-situ sowing requires that the soil should be fine, like that of a seedbed. For an even finer tilth, sprinkle compost over the top of the bed and lightly rake it in. The seeds can be sown directly into the soil and will germinate easily.

Step nine: Water the bed with a watering can or hose with a fine rose nozzle that won’t splash the soil. Let it stand for two days before sowing.

Tip: Mulch the pathways with lawn cuttings, pruned vegetation and other organic material that breaks down as you walk on it. When the bed is being prepared for a second crop, scoop about 5cm of soil from the pathway (which includes all the organic material), put it on the bed and then add 5 to 10cm of compost before turning it in with a fork. All the clumps go back into the pathway to be tramped over and broken down. In this way, the pathway is used to build the fertility of the bed.

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Covering Crops

Poor soil can be enriched by planting cover crops as a green manure. As soon as the crop starts to flower dig it into the soil. The plants should not be allowed to flower or fruit because the aim is to enrich the soil. Mustard leaves, borage, broad beans and peas are ideal cover crops because they add nitrogen and other minerals to the soil.

Options For Veggie Beds

We are all different. Some of us are straight up and down types; others like to go around in circles! Choose the kind of bed that suits your personality.

Conventional, rectangular beds produce a well-ordered food garden, easy to plan and work in. A border of 30cm on either side of each bed allows for expansion; for future pathways and beds. The bed width of 1m allows the centre to be reached from any side. A border of 1m surrounds the garden for wheelbarrow access.

An alternative to the 1m wide beds is to make narrower 60cm wide beds that comfortably allow one to straddle the beds when working on them.

Keyhole beds are often used in permaculture and are regarded as being the most efficient kind of bed because it is easy to work in them. They have a keyhole or horseshoe shape which allows you to stand in the centre and work from there.

Eco circle beds consist of a single 1m diameter circle or three 1m diameter circles that connect but not overlap to form a clover leaf circle. Usually, a pest repellent herb is planted in the centre of the cloverleaf circle. A 20cm diameter pot with drainage holes is sunk in the centre of each circle and vegetables are planted about 15cm from the pot. The veggies are watered by filling the pot with water which drains out at root level. These beds are ideal if water is scarce or not easily accessible. It also allows for natural pest control through companion planting.

Square foot beds are one metre by one metre, further divided up into a grid, with each block corresponding roughly to the size of a foot. This provides enough space for 16 different crops so companion planting and diversity is easy to achieve. The benefit of this bed is that you tend to sow what you need and not over sow because of limited space.

Wagon wheel is usually used for herbs but also works with a combination of vegetables. The pathways make it easy to access the herbs and vegetables.

Raised built beds are easier to work if you have back problems. They require a greater initial outlay and effort and are permanent. They act as giant containers so will need good drainage and will have to be filled up with new soil and compost fairly regularly. They are also a solution for sloping areas.

Lasagna gardening is a term adopted in the United States but is basically the same as sheet mulching. The soil is not dug over but alternate layers of organic material and garden soil are built up, like lasagna! The assumption is that earthworms and other microorganisms will move upwards. However, if there is limited biological life in the soil it will take a long time for the bed to reach the stage where vegetables can be planted. This is particularly a problem if the virgin soil is compacted.

Mono-Cropping or Poly-Cropping?

Mono-cropping refers to the commercial agriculture practice of planting hectares of the same kind of crop. In a residential garden, planting the same veggies together in one bed does not have the same effect because there is usually enough diversity in the surrounding garden to attract birds and beneficial insects. Poly-cropping is an equally valid choice as it ensures diversity through companion planting that puts together beneficial herbs, vegetables and flowers.

Checking The Soil PH

The ideal soil for vegetables has a ph of 6.5 to 6.8. The ph can be checked with a soil ph meter which is easily available from a garden centre or hardware centre. Make sure the soil is moist before putting in the meter and leave it in place for a while before taking the reading.

Soil with a ph in this range does not need lime. Should one want to add lime, it should not be more than half a cup per square metre every two or three years. Soil that has been over limed will take three to four years to correct. If the alkaline levels are too low it is better to use azalea compost or pine needles to raise the acid level in the soil.

With all of this out the way, the only thing left to do is purchase a wonderful set of herb markers.