Soil is the secret to a thriving garden

Learn how fall changes, like compost, manure or pH adjustments can set the stage for resilient plants next spring

Healthy garden soil is key to growing vigorous and resilient plants. Soil serves not only as a solid base for anchoring roots but also as the primary vehicle for delivering water and nutrients to plants. Gardeners commonly amend soil with organic matter to improve the availability of water and nutrients to plant roots. Another reason to amend soil is to adjust the pH to support certain plants, such as blueberries or hydrangeas. Whatever your goal, amending soil takes time. Fall is a good time to amend the soil in preparation for planting next spring.

Improving Soil Structure with Organic Matter

Organic matter is a term used to describe living and dead materials derived from plants or animals, such as decomposed plant tissue, composted manure or grass clippings. Incorporating organic matter into clay soil improves drainage by creating larger pore spaces. In sandy soil, organic matter provides a place for water and nutrients to bind, making these more available to plants. Soils rich in organic matter also support more biological activity and beneficial organisms.

Many types of organic matter can be used to amend soil including composted and uncomposted (or raw) materials. These differ significantly in their nutrient content as well as the ratio of carbon to nitrogen, which in turn impacts nutrient availability in the soil. For example, animal manures tend to be rich in phosphorous and potassium, nutrients that can easily build up to excessive amounts in soils. Composted plant materials, typically referred to simply as compost, also can contain high levels of certain nutrients.

Composted manure and plant compost can be used in large quantities when building up degraded soil or establishing new planting beds but should be used more judiciously in established beds. For new beds, incorporate 3- to-4-inch layer into the soil. Apply manure and compost sparingly in established garden beds to prevent nutrient build-up, top dressing with just one-half to 1 inch. Always use well composted manure rather than fresh.

When building new beds, uncomposted plant materials such as leaves, grass clippings, straw and wood chips can be incorporated into the soil to improve soil structure. These materials decompose directly in the garden and are best applied in fall. Microbes utilize nitrogen and other nutrients as they break down these carbon-rich materials. As a result, nitrogen can become limited in beds where raw organic materials are used. Conduct a soil test in early spring and fertilize according to test results.

Amending Soil pH

Another reason to amend soil is to adjust soil pH. Most garden plants perform best in soil with pH between 6.0 and 7.0, as plant nutrients are most available within this range. Of course, there are always exceptions. Certain conifers, many broadleaf evergreens, and blueberries grow best in acidic soil (pH 5.5 to 6.0), while viburnums and lilacs grow best in neutral (pH 7.0) to slightly alkaline (pH 7.5-8.5) soil. While the easiest approach is to only grow plants adapted to your existing soil conditions, this is not always realistic. Likewise, soil can naturally fall well outside the ideal range.

Lower soil pH and increase acidity by incorporating sulfur into soil. Amend with lime to increase pH or make soil more alkaline. Application rates will depend upon the existing soil conditions, soil type, and the desired change in pH. Conduct a soil test and consult your local County Extension Office to determine specific needs.

Soil pH takes several months to stabilize and can change over time. Begin amending soils in fall for spring planting and continue to check soil pH yearly, making further adjustments as needed.