Amending garden soil is a task that is so important especially for the vegetable gardener, if the best results for your efforts are to be forthcoming. All garden soil will become ‘weary’ over time simply due to the leaching away of the minerals present, especially by nitrogen hungry vegetables such as tomatoes, peppers, corn, cucumbers etc.
The best time to amend the soil (which simply means to improve its value for growing plants), is in the Autumn period before the start of winter proper. This is the time when the soil is not too wet or dry, and any additions will have over winter to ‘work in’ or become established with the existing soil.
The Springtime before the growing season begins is a good ‘second best’ as there is no time for real integration to take place before the growing starts, however if you miss the Autumn for any reason then the Spring is the next best thing.
What is the difference between soil amendment and fertilizer?
To amend garden soil is to add products that will make the soil more workable or ‘friable’. To bring the soil into optimum condition for growing plants. Although there may be minerals added such as Gypsum or lime or calcium to aid plant growth and performance.
The addition of organic material is an important aspect of soil amendment as it loosens up the soil creating oxygen pockets that allow for strong root growth as well as creating adequate drainage.
However this is where there is a slightly ‘grey area’ to consider. Organic material such as compost or manure when added to the soil acts both as a soil amendment AND a fertilizer as the nutrients from these products feed the plants while the physical components help with soil amendment.
To clarify a little further…compost is not the same as fertilizer – although it is often treated as such. Compost feeds the soil and improves soil conditions as described, where fertilizer feeds the plant direct.
Plant fertilizers contain 3 vital macro nutrients that plants need for healthy growth, and these are Nitrogen, Potassium and Phosphorus, and many micro nutrients besides.
For this reason many store-bought composts have ‘added minerals’ to improve your plant growth. This is also why organic gardeners in particular will use more composting and soil amendment methods in order to keep the land in prime condition – rather than just feeding the plants with fertilizers which can leave the land itself barren and lifeless.
Keeping the land healthy with the use of organic materials added on a regular basis will improve the land and keep it productive for years to come – just look at the history of Amazonian Dark Earth
‘Terra Preta’ (black soil), still the most fertile soil on the planet and produced centuries ago!
What does feeding the soil mean?
In effect that is what soil amendment is all about. ‘Feeding the soil’ is a simple descriptive phrase for improving the soil conditions for the plants, but also so that worms and beneficial microbes & insects will be encouraged to live there and improve it further with their activities.
By creating a good habitat for these insects and microbes you are giving nature a ‘helping hand’ and benefiting enormously in the long term from their activities.
The aim of the organic farmer is to ‘feed the soil and not the plant’ Meaning that by keeping the soil in good condition, both the plants and nature itself will benefit.
Best soil amendment materials?
Best materials for soil amendment include the following…
- Home made, well rotted or aged compost
- Composted or aged manure preferably horse, cow, chicken, goat or rabbit
- Sphagnum peat
- Rotted leaves from the previous fall
- Vermiculite or pearlite
Applying soil amendment material
Once you have chosen your soil amendment material it is time to look at applying it to the soil.
The process is similar to mulching in that you apply a coat of material 2-3 inches think all around the area of choice. However instead of just leaving it on the surface as you would a mulch, you get a garden fork and dig it into the soil by turning it over thoroughly.
This process will ensure that the amendment gets to where it is needed, aerates the soil and improves moisture retention or drainage depending on what your end goal is.
Leaving this mix for several months before planting will only improve the amendment process.
Choosing the best amendment for your soil
At the risk of stating the obvious – Not all soil types are the same!
Basically there are 4 main soil types you may have that can create problems for the vegetable gardener…
- Sandy soil that will drain quickly and have little in the way of natural nutrients.
- Clay soil that may hold water and nutrients but become boggy and waterlogged without treatment.
- Silt soil is usually nutrient rich and slick or slippery.
- Chalky soil is alkaline in nature and low in plant nutrients.
As well as these 4 main soil types you also have loamy soil (gardeners dream soil) that is really the ideal soil for most vegetable plants.
Treatment for these soil types are as follows in the chart below.
| SOIL TYPE | IDENTIFY | TREATMENT |
| SANDY SOIL | Take a handful of damp soil and form a fist. Compress and then open you hand. If the soil will not hold in one piece then it is sandy or gritty soil | Most veggies like sandy soil and free drainage, but also like plenty nutrients. Add a load of organic material including rotted manure to the soil. Adding vermiculite will also improve nutrient and water retention |
| CLAY SOIL | Repeat the test for sandy soil. If the soil holds firmly together then you have a high clay content | Adding organic material will improve nutrient value whilst the addition of sand will improve drainage |
| SILT SOIL | The same test as above but the soil will retain partial shape and be slippery and smooth to touch | Silty soils tend to be slightly acidic in nature and can be slow draining if clay content is high. Treatment is similar to that for clay soil |
| CHALKY SOIL | A good test is to put a spoonful into a jar of water. If it froths up then it is loaded with calcium carbonate or limestone | Alkaline in nature, chalky soil needs the addition of well rotted or aged manure, composted pine needles, leaf moult and other organic material. |
Winter cover crops:
In addition to the measures described above, you may also consider planting a winter cover crop. This can help to both add valuable nitrogen into the soil when using legumes as a cover crop, as well as add valuable organic material into the soil when it is ‘dug in’ in the Spring.
Cover crops also prevent water erosion and the leaching away of soil nutrients over a wet winter period.
Cover crops should be planted in the late summer when there is still enough heat for growth, but the crops will not have to compete with heavy weed growth at the same time.
Good plants for winter cover crops include winter field beans, peas, and other hardy legumes which make excellent nitrogen fixers. Crimson clover, winter wheat, buckwheat, vetch, and winter rye.
Other ways to cover your garden area over winter include covering with mulch, weed fabric, or even old carpet. None of these methods will add nutrients obviously (with the exception of some mulch types), but they will help prevent the nutrients leaching away over winter and also prevent weed growth.
Conclusion:
No matter what the condition of your soil and its ability to grow healthy vegetables, for most of us the soil conditions are not ideal and so the need for soil improvement is an on-going issue.
This is not however a bad thing! Gardening is after all taking care of the garden either for aesthetic or practical purposes, and is what makes this such a rewarding experience both for the body and for mental health.
As for the best time to get to work with soil amendment, the late Autumn is without doubt the best time before the soil gets freezing or water-logged. Failing that, early Spring will do at a pinch, before planting out begins in earnest.
Now where did I put that garden fork…
