Monday, 14 March 2011

Planting Vegetables - Seed-bed Preparation

Preparing a good seed-bed is the first part of growing a succesful vegetable garden. My backyard has previously been used for growing vegetables which has both benefits and some negatives. The benefit of inheriting a plot previously worked, is that the job of digging may be easier, which on a hot summer's day is a bit of a blessing.

The negatives are; you have no idea of what was grown where. This is important because of what is called 'the rotation' and comes from the desire to not grow the same type of vegetable in the same location, year after year. Rotation is critical to minimise the risk of soil diseases which can build up over time, particularly important if you are like me and you don't want to spray your vegetables with chemicals. 

If your plot has never been cropped before, start by chipping away the top layer of grass and weeds down to the soil surface. Skim the face of the blade over the soil, trying not to dig more than a few centimetres deep separating the sward (top) from the roots. This will leave the majority of the topsoil intact. Lift this part of the sod to one side of the bed. If you have a compost heap, this can be incorporated into the mound. If not, then dig a full spade depth deep and then bury this plant material to rot.

Once the soil surface is clear of weeds, dig to a full spade depth and invert the divet. This will aerate the soil and loosen up the soil structure, breaking up compacted layers that may have formed from factors such as foot-traffic or heavy winter rain.  

Break up the larger clods of soil with your spade or garden fork until a 'crumbly' structure is achieved. If seeds are to be sown, the soil texture in the upper layer needs to be very fine - perferably the particles should not be larger than 1mm - 3mm in size, as small seeds require close contact with the soil. If the structure is too coarse, then the germination of the seed may be affected.
Where transplants are to be grown then the seedbed can be more forgiving, however a consistent even tilth is still desirable.

Once the seed-bed has been dug-over, it is time to add soil ammendments such as compost. The nutrient rich, semi-digested organic matter, will act both as a plant fertiliser and enhance the activity of soil microbes which benefit plant growth.

Incorporate the compost to the full spade depth. This will improve drainage within the seed-bed and offer extended nutrient supply for the full growing period as the root systems of mature plants reach the bottom of the soil profile.

In addition to compost, lime or dolomite can be added to help raise the soil pH. Lime adds calcium and Dolomite adds both calcium and magnesium.

Raising soil pH is important for vegetables such as brassicas which includes broccoli, cabbage and cauliflower. Higher pH can reduce the risk of soil diseases called 'club root' that specifically affect brassica.

Increasing soil calcium levels is also beneficial to other veges. It can improve quality and shelf-life of lettuce and reduce the risk disorders such as blossom-end-rot of tomato and capsicum. We will cover all of these in later blogs as we progress through the growing season.

Seed-bed ready for planting

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