Soils in established gardens can become very undernourished over time unless careful maintenance is used. The loss of organic matter by the continual tidying and removal of leaves and prunings leaves the soil hungry and depleted with minimal worm and micro-organism activity. When major soil amendment is not possible because of existing roots of trees, shrubs, perennials and lawns it is still possibly to make significant improvements in the soil.
With the exception of fungi, nearly all soil micro-organisms and worms need a moist environment to operate successfully in. If soils have dried out and become hydrophobic then you will need to treat that first. Keep soils moist and spread manures over the top – no more than 5cm thick, and allow the soil fauna to drag the manures into the soil. Once manure has disappeared, can repeat manure application or use a pea or lucerne straw mulch. This will add organic material as well as keeping soil moisture at good levels for the worms and soil micro-organisms to operate effectively. If available, spreading liquid worm waste from worm farms is greatly beneficial.
For a more concentrated fertilizer ‘hit’, use the pelleted form of manure based fertiliser and sprinkle over the soil before spreading mulch. It can also be used when mulch is topped up. Controlled release fertilizers can also be used in conjunction with mulch, these will aid plant growth, but do little to improve your soil directly. However, increased root growth assists many soil micro-organisms as they live in the rhizosphere (area immediately adjacent to and on the roots).
Minimise soil compaction using organic mulch and managing foot traffic. Compacted soil loses the essential pore space for gas exchanges and for water to move through. Soil compaction is much more rapidly done and serious when the soil is wet. Avoid walking on wet soils where possible and use thick mulch on paths to reduce impact of foot traffic.
A commercial aerator (either a corer or a spiked roller), can be used to aerate soils without causing too much damage to plant roots. After aeration, spread manures or compost over and rake through.