Once your patch has been created, most of the hard work is done. Now your two main tasks will be to maintain the soil fertility, and manage weeds.

There are several different factors of your soil layer that you will want to pay attention to maintaining. These include nutrient levels, pH (acidity/alkalinity), soil structure and drainage.

The short version of the story to maintaining a healthy soil layer, is to add good compost regularly (about once a year or more often, depending on intensity of cultivation), add lime once every 1-4 years at application rates suggested on the packet, fertilise your plants during growth (especially heavy feeders) with liquid fertilisers such as urine, liquid seaweed, or comfrey tea, or using mulches such as pea straw or comfrey leaves. After harvest turn the soil over to mix in the partially broken down mulch layer to increase the friability of the soil.

NUTRIENT LEVELS can be supplimented in a couple of ways. This is by either the addition of organic matter and minerals from outside sources (e.g. compost, comfrey leaves, seaweed, manure, straw, leaves, grass clippings etc), or by 'green cropping' with legumes, which 'harvest' nitrogen from the air and fix it into the soil using nodules on their roots. A good soil layer requires the presence of the main nutrients required for plant growth - Nitrogen, Phosphorous and Potassium, as well as a selection of other 'minor' nutrients and trace elements. Different plants enjoy different ratios of nutrients, with plants that grow a lot of green bulk like leaves requiring lots of nitrogen, while flowering / fruiting vegetables require higher levels of Phosphorous and Potassium. Details on each plant's preferences can be found in the species specific section of this book. The easiest way to ensure that you're getting a good range of nutrients added to your soil is to add a variety of things to it, rather than just one thing such as manure. Seaweed is an excellent source of a wide range of nutrients and minerals. If you've added a lot of raw (not pre-composted) ingredients to a garden bed, you may need to let it sit for a few weeks to allow the materials to break down a bit before planting.

ORGANIC SOURCES FOR SPECIFIC NUTRIENTS

HOME MADE FERTILISERS

Click HERE to go to the page for home made fertilisers, including comfrey tea, liquid seaweed, urine, and mulches.

pH (acidity / alkalinity)

Different plants prefer different pH ranges. On the pH scale of 1 to 14, 7 is neutral pH, with below 7 being acidic and above 7 being alkaline. Different pH levels affect the bio-avaliability of the soil nutrients to your plants roots, as illustrated by the picture below.

There are several ways of keeping an eye on the pH of your soil, including inexpensive pH test kits (avaliable at garden centres), litmus paper, or observations of the growth habits of the plants and any pH related diseases / problems that you may see arising.

The decomposition process of organic matter within the soil usually results in a gradual shift toward acidic soil. For 'all purpose' use garden beds it is best to keep the pH near neutral or ever so slightly acidic. pH can be adjusted back toward neutral from acidic using lime. It's best to use lime in as raw of a form as possible, such as crushed limestone or dolomite lime. The more processed forms of lime, such as hydrated lime, are very potent and you can easily overdo it or burn your plants with them. The raw forms are slow release and only need to be applied once every 1-4 years depending on your application rate and preferences.

SOIL STRUCTURE AND DRAINAGE

Again, different types of vegetables prefer different types of soil structure, with some preferring denser, boggier soils, some liking light, humusy soils, and so on. In general, it's good to aim for a middle ground, where the soil is free draining but also holds a decent amount of moisture. If the soil becomes really squeltchy / muddy when it's wet, or if puddles form, you probably need to take action to improve the drainage. One method is to build the border of your patch higher up and fill that with light, friable soil materials like straw, hay, dried grass clippings, dried leaf rakings, etc. This can then be mixed in with the bottom soil layer and should improve the overall drainage. If the problem is really serious you may need to dig out your soil layer and create some drains underneath by digging trenches and filling them with stones, ceramic piping, etc. before covering over again with dirt.

For more info read AN AGRICULTURAL TESTAMENT By Sir Albert Howard  One of the classic texts on organic gardening, with comprehensive info on soils, different composting techniques and soil fertility. 

SOIL LINKS:

http://soils.usda.gov/sqi/concepts/soil_biology/fw_soilhealth.html an interesting site about soil biology and more