Nitrogen, phosphorus, and potassium are macro-nutrients which are vital for healthy plant growth. Calcium is essential for building healthy cell walls within plants. Eggshells are composed of calcium carbonate and can easily be added to soil (courtesy: SoutheastAgnet.com).
By John Green, Certified Texas Expert Gardener, Orange County, TX
Now that Spring is here ‘officially’, most of us are scurrying about outdoors, intent on making garden beds ready for ornamental plants, herbs, and vegetables. There are numerous gardening tasks which must occur to provide plants with the best growing medium and optimal environment possible. It is important to provide plants with nutrient dense (macro and micro-nutrient availability), pH balanced soil that is friable which satisfies plant-specific growth requirements while supporting the soil’s microbiome, a complex community of microscopic life forms. Soil amendments are essential not only for plant growth but also for enhancing soil structure and increasing nutrient availability. Years ago (as a novice gardener) it was my belief that soil amendments were needed strictly for immediate plant health (during a single season). Through years of gardening and trial and error, I’ve learned that managing soil health involves practices that maintain and enhance its qualities to support a healthy ecosystem.
The reasons for supporting our garden soils microbiome can become a bit technical and detailed which is why I’m presenting a scaled down version of the more technical information to provide readers understanding as to why ‘feeding’ the soil’s biome is so important to plant health and the symbiotic relationship that exists between the “community” within the soil and nutrient availability to plants.
The soil microbiome consists of bacteria, fungi, archaea (prokaryotic organisms that are single-celled, without having a defined nucleus), protists (eukaryotic organisms that are most often single-celled organisms as well though not classified as animals, plants, fungi), and viruses. Soil virus composition, also known as ‘viral abundance, plays a distinct role in regulating host dynamics and soil ecology. The viral composition is directly influenced by factors such as soil pH, temperature, moisture, chemistry, and environment, all coexisting within the soil. These microbes are essential for soil functions, including:
- Nutrient Cycling- adding organic matter for decomposition releases nutrients plants can absorb.
- Soil Structure- aggregating soil particles to improve structure and water-retention capacity.
- Pathogen Suppression- some microbes can inhibit the growth of harmful pathogens and protect plants from diseases.
- Plant Growth- certain microbes promote plant growth (producing substances which aid plant growth) and improve nutrient uptake.
Amending garden soil is a process which requires focused attention multiple times during growing seasons and throughout the year. Adding a 1 to 2-inch additional layer of mulch, leaf mold, or composted manure at the beginning of the growing season is an excellent beginning for limited nutrient availability but more is needed, meaning additional amendments will be necessary more frequently. My preference is by amending vegetable and ornamental beds with a 1 to 2-inch layer of well-aged, composted manure multiple times during the growing season (turning or raking into the soil with a garden spade), followed with a 1 to 3-inch layer of mulch necessary for moisture retention, temperature equilibration (warm during winter & cool in summer), and weed suppression.
As gardeners, we should occasionally take a moment to think about the amendments we are adding to our gardens and why? Sometimes the ‘stuff’ (technical term) added to the garden is valuable- beneficial to soil and plants, sometimes the ‘stuff’ added isn’t impactful, and other times the addition was detrimental, harming the soil and plants. There are many common practices which gardeners share amongst our group, most of which are beneficial. Let’s review a couple common practices which many gardeners utilize as soil amendments.
Coffee Grounds
Many gardeners (including myself) avoid composting yard debris due to aesthetics, limited space, time constraints, or other constraints such as mine… the inability to keep livestock out of compost bins (seems to be their preferred playground)! Composting can take on many forms and does not necessarily require a large space or a large volume of debris. For individuals new to gardening or interested in starting a compost bin, it is advisable to begin with small amounts of debris, such as kitchen vegetable scraps (excluding meat scraps, bones, grease, or cooked vegetables). Coffee grounds are beneficial to the soil due to the small amounts of nitrogen they add. Contrary to popular belief, small amounts of used coffee grounds will not increase soil pH. Disperse the grounds into a thin layer atop soil and mix them into the soil to avoid forming a thick layer.
Eggshells
Nitrogen, phosphorus, and potassium are macro-nutrients which are vital for healthy plant growth. Calcium is essential for building healthy cell walls within plants. Eggshells are composed of calcium carbonate and can easily be added to soil. Prepare the eggshells by drying them thoroughly in the oven. Once dried, break the shells into smaller pieces and place them into a blender or spice grinder. Some gardeners add one or two cups of water to the blender, then pulverize. My preferred method is to use a large mortar and pestle to allow precise control of particulate size. Some batches are intentionally larger pieces that are scattered on top of the soil as a snail & slug deterrent. Grinding shells into a fine powder will decompose into the soil faster, making nutrient availability occur sooner.
Eggshells are enjoyed by the brassica family group (cabbage, broccoli, kale, kohl rabi, Brussel sprouts) but are best avoided as nutrition for acid-loving plants, such as rhododendrons, blueberries, camelias, and hydrangea.
Calcium enters plants through actively growing root tips, moving through the plant and into the fruits along with water, via transpiration. Root damage or problems with water uptake and movement in the plant limit the amount of calcium reaching the fruit. An overabundance of magnesium and ammonium in the soil will interfere with calcium uptake.
Epsom Salt
Occasionally, gardening posts on social media, blogs, magazine articles, and many experienced gardeners espouse the benefit of using Epsom Salt for increased flower production (especially in roses), and vegetable crop yields. It is evident to me that (after research) before using Epsom salt, that gardeners have soil tested by a soil testing laboratory. Contact the local County Extension office, who can provide soil testing forms and detail the process to capture soil samples. Soil analysis cost is minimal, most often less than $20.
Unless the soil analysis report confirms a need for magnesium, do not add Epsom salt to any garden area. Adding Epsom salt for ‘everything’ is a widely distributed gardening myth and is not beneficial to plants and interferes with the uptake of other nutrients. Epsom salt will not prevent blossom end rot!
Understand that adding too much magnesium to the soil will prevent calcium uptake from getting into tomato plants, making blossom end rot dramatically worse! Adding Epsom salt to soil which has sufficient magnesium will harm the soil and plants, such as by inhibiting calcium uptake.
Until next time fellow gardeners, let’s go out and grow ourselves a greener and more sustainable world, one plant at a time! Please continue sending gardening questions to: jongreene57@gmail.com.
Social Media