Raised Bed Media and Nutrient Program After Compost Delivery
A community garden coordinator has 12 raised beds, each 2.4 m × 1.2 m × 0.35 m deep, to be filled to 50 mm below the rim. She plans to mix 40% screened green-waste compost, 40% topsoil stripped from a nearby paddock, and 20% coarse sand by volume. The compost was delivered three weeks ago and has been stored in a tarped heap that now smells sour and has grey-white mould patches. The paddock topsoil is a heavy clay loam that crusts after rain. The garden grows leafy greens, tomatoes and carrots, and the group wants to avoid bagged fertiliser for cost reasons. Two beds already contain established rosemary and lavender that have grown poorly and turned pale.
1. Evaluate the proposed mix and storage practice, and recommend changes before filling.
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The mix needs rework on several counts. By volume, 40% heavy clay topsoil plus 20% sand leaves a dense, poorly drained blend; sand added to clay in that proportion can create a concrete-like matrix rather than improving structure. For raised beds only 350 mm deep, drainage and aeration matter more than native soil content. Recommend reducing topsoil to about 20%, raising compost to 50–60%, and using a coarse bark or aged pine fines component in place of much of the sand. The sour smell and grey-white mould indicate anaerobic decomposition from tarping wet material; this compost may still be usable but must be turned, aerated and allowed to mature, and it should not be used fresh around seedlings. Test it for maturity and salinity before use. The pale, poor rosemary and lavender suggest alkaline, wet or compacted conditions - these herbs dislike rich, moist media, so keep them out of the vegetable mix and improve drainage around them separately. Also confirm the compost meets local green-waste contaminant standards and check pH and electrical conductivity of the final blend before planting.
2. The group wants to avoid bagged fertiliser. Outline a nutrition strategy for the first two seasons and explain how crop choice affects it.
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Rely on compost plus mineral and organic amendments rather than soluble bagged products. Before filling, incorporate mature compost at the planned rate and add a slow-release phosphorus source such as rock phosphate or steamed bone meal, plus a potassium source like wood ash or sulphate of potash where pH allows. Check pH first: most vegetables want 6.0–7.0, and wood ash raises pH, so avoid it if the blend is already alkaline. Use legume green manure or a pea/bean rotation in the first season to build nitrogen, and mulch with compost between crops. Crop choice matters: leafy greens and tomatoes are heavy nitrogen feeders and will need the richest beds; carrots fork and distort in fresh manure or lumpy compost, so give them the most settled, finest-textured beds and low fresh nitrogen; rosemary and lavender want lean, free-draining, low-fertility conditions and should be kept separate. Plan a rotation so heavy feeders follow legumes, and monitor with a soil test after season one rather than guessing.