(News article from September 18, 2025)

Caring for the health of your soil is important for healthy landscapes, yards, vegetable gardens, and fruit trees. Last week’s column discussed essential nutrients required by plants for healthy growth. We also looked at how soil pH affects nutrient availability, along with soil texture, compaction, and organic matter. Today we will continue the topic of improving soil productivity through soil amendments and fertilizers.

A soil rich in organic matter and microbial activity, good water flow and holding capacity, and good structure – not too loose or too compact – is the goal for a successful garden and landscape. Very few soils are like this to begin with. This means we will need to amend the soil. Soil amendments are any material, typically organic in nature, that is added to the soil to improve the physical properties of water retention, permeability, and aeration.

Common soil amendments include compost, peat moss, finely shredded bark, composted manures, incorporated cover crops, cotton gin trash, sugarcane bagasse, and mushroom compost. Aside from peat moss, allowing these materials to age or compost will result in a better-quality amendment. Adding fresh organic matter, especially organic matter high in carbon, like bark that hasn’t had time to begin decomposing, will draw nitrogen out of the soil and away from plants. These materials should be aged or composted between 6 to 12 months before incorporating into your garden.

Soil amendments are used to improve what is referred to as soil tilth – the physical quality and structure of a soil. These amendments (aside from manures) are not intended to be fertilizer, although they do contribute nutrients to the soil. Alone, they do not contain enough nutrients to supply the necessary quantities needed by plants, especially in soils that are deficient.

Fertilizers are the primary sources for plant nutrients. These can be either synthetic or organic in nature. Common synthetic fertilizers we use for home gardens and landscaping include 13-13-13, 8-8-8, 8-24-24, ammonium sulfate, calcium nitrate, urea, triple super phosphate, muriate of potash, and slow-release fertilizers. Slow-release or controlled release fertilizers are encapsulated by a protective coating designed to slowly dissolve, gradually releasing the nutrients. Typically, slow-release fertilizer takes around 3 months to fully dissolve in our climate.

Synthetic fertilizers have the advantage of being quick acting and highly concentrated sources of nutrients. This makes them a relatively fast, convenient, and low-cost way to fertilize plants. The disadvantages of synthetic fertilizers include being short lived, increased leaching and runoff, fertilizer burn to plants from over or incorrect application, and accumulation of fertilizer salts, which are damaging to plants, when there is insufficient rainfall or irrigation.

Organic fertilizers come from sources that were once living. Common organic fertilizers we use include animal manures, bone meal, blood meal, cotton seed meal, fish emulsion, seaweed extract, and green manures such as legume cover crops. Because these sources have a high amount of organic matter, they have lower salt concentrations and are less likely to damage or burn plants. They also have the advantage of improving soil structure and microbial health, being a complete nutrient source.

Disadvantages or organic fertilizers include nutrients may not be readily available for plant uptake, lower nutrient concentrations than synthetic, difficulty in applying precisely because nutrient concentrations are not fixed, slower outcomes, and dependence on soil microbes to release nutrients to plants. Organic fertilizers need time to become active in the soil, making them a great natural, slow-release fertilizer. Just be mindful that the sole use of organic sources will require larger quantities, planning, and patience.

When you apply fertilizer is just as important as what fertilizer you apply. For example, in vegetable gardens it is best to incorporate half the amount of fertilizer recommended 10-14 days before you plant to the root zone of the plant – the top 6 to 8 inches of soil. The remaining amount is applied as side dress applications – incorporating next to the plants – during the growing season. For landscaping and fruit trees, it is best to apply in early spring as plants start to wake up from winter dormancy. Lawn fertilizers should be applied overtime when they are actively growing, with applications made in April, June, and early August. Unless you are growing cool season bedding plants or vegetables, fertilizers should not be applied going into fall and winter.

Following university extension fertilizer recommendations is a good source for making sure your plants are receiving the appropriate amount of nutrients needed to sustain healthy growth. Whether you use synthetic, organic, or both sources of fertilizer, how and when you apply is equally important.