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Soil Amendments Guide: Greensand, Rock Phosphate, Biochar & More

Complete guide to soil amendments: greensand, biochar, rock phosphate, bone meal, kelp meal, and more. What each does and how to use them.

What Is It ?

Soil amendments are the long game of gardening — they do not feed your plants today, they transform your soil so it feeds plants better for years to come. While fertilizers deliver specific nutrients in measured seasonal doses, amendments change the fundamental character of your soil: its physical structure, water-holding capacity, microbial diversity, mineral content, and pH buffering ability. Old Cobblers Farm's Wicked Organics line includes a complete range of soil amendments that work together to build exceptional soil from the ground up. Greensand adds potassium and 30+ trace minerals while improving soil texture in both sandy and clay soils. Bio Char creates permanent microscopic habitat for beneficial soil organisms that persists for centuries. Rock Phosphate builds a multi-year phosphorus reserve that feeds without leaching. Bone Char provides both phosphorus and activated carbon in a single product. Kelp Meal delivers natural growth hormones and micronutrients that standard NPK fertilizers completely miss. Tea Seed Meal conditions soil with natural saponin compounds while adding over 50% organic matter. The distinction between amendments and fertilizers matters: amendments build the soil itself, while fertilizers feed the crop in that soil. The best gardens use both — amendments as the permanent foundation and fertilizers for targeted seasonal nutrition on top of that foundation.

Understanding the Difference Between Amendments and Fertilizers

Fertilizers and amendments are both things you add to soil, but they serve fundamentally different purposes. A fertilizer is like feeding a person a meal — it provides specific nutrients that the plant needs right now to grow, bloom, or produce fruit. An amendment is like renovating the kitchen — it changes the environment itself so that meals can be prepared more efficiently for years to come.
When you apply Wicked Growth 10-10-10, you are feeding the plant. When you apply Wicked Organics Bio Char, you are upgrading the soil. Both matter. But the order matters too: building great soil first and then fertilizing within that great soil produces dramatically better results than fertilizing mediocre soil year after year without improving it.
This is why experienced gardeners and farmers invest in amendments even though the benefits are not immediately visible. The payoff comes over seasons and years as the soil becomes darker, looser, more moisture-retentive, and more biologically active. Plants grown in well-amended soil need less fertilizer, resist diseases more effectively, tolerate drought better, and produce higher yields than plants grown in unamended soil receiving the same fertilizer program.

Wicked Organics Greensand (0-0-3)

Greensand is an ancient ocean mineral deposit — technically called glauconite — formed on the seafloor millions of years ago when marine organisms deposited iron-rich minerals in layered sediments. It contains potassium (3% K2O), iron, and over 30 trace minerals including silica, magnesia, manganese, and calcium. But Greensand's real value extends far beyond its modest nutrient content.
The unique crystalline structure of glauconite absorbs up to one-third its weight in water, making it an exceptional soil conditioner. In sandy soils that drain too fast, Greensand acts like tiny sponges that hold moisture in the root zone. In clay soils that hold water too tightly, Greensand particles physically open up the soil structure, improving drainage and air circulation around roots. In any soil type, it improves cation exchange capacity — the soil's ability to hold and release nutrients — meaning fertilizers you apply alongside Greensand work more efficiently.
Unlike chemical potassium sources like Muriate of Potash that deliver nutrients in a burst and are gone, Greensand releases potassium and minerals slowly over years rather than weeks. This makes it virtually impossible to over-apply. You cannot burn plants with Greensand, and you cannot create the salt buildup problems that come from heavy use of synthetic potassium sources.
Old Cobblers Farm's Wicked Organics Greensand is OMRI-listed for certified organic production. Apply 5-10 pounds per 100 square feet and work into the top 6 inches. One application continues improving soil for 2-3 years. For maximum benefit, combine with Bio Char and Kelp Meal for a complete soil amendment program.

How To Store

Bio Char is carbon that has been heated to extremely high temperatures (700-1000°F) in a low-oxygen environment — a process called pyrolysis. The result is a material with billions of microscopic pores that act as permanent housing for beneficial soil microorganisms. Each tiny pore provides shelter from predators, a stable environment with consistent moisture and temperature, and surfaces for beneficial bacteria and fungi to attach and colonize.
The key word is permanent. Unlike compost or mulch that decomposes over months, Bio Char persists in soil for centuries to millennia. Archaeological sites in the Amazon basin contain charcoal-enriched soil (terra preta) created by indigenous peoples over a thousand years ago that is still dramatically more fertile than surrounding soil. Bio Char is a one-time investment that keeps improving your soil indefinitely.
Beyond microbial habitat, Bio Char's porous structure holds water and dissolved nutrients. In sandy soils, this is transformative — Bio Char-amended sandy soil can hold 2-3 times more water and nutrients than unamended sand, reducing irrigation frequency and fertilizer waste. Every bag of Wicked Growth or Wicked Organics fertilizer you apply to Bio Char-amended soil works more efficiently because nutrients are held in the root zone rather than leaching through.
Wicked Organics Bio Char is OMRI-listed and works in any soil type. Apply at 5-10% by volume mixed into the top 6-8 inches. For best results, charge Bio Char before incorporation by soaking it in compost tea, worm casting extract, or a dilute solution of Wicked Growth 19-19-19 for 24-48 hours. This pre-loads the pore spaces with nutrients and microbes so the Bio Char starts working immediately rather than initially absorbing nutrients from your soil during its first season.

Wicked Organics Bio Char

Rock Phosphate is finely ground mineral rock — primarily apatite — that provides slow-release phosphorus over 3-5 years from a single application. This extended release timeline makes it fundamentally different from water-soluble phosphorus sources like Triple Superphosphate. Where TSP delivers phosphorus in an immediate burst that can leach into waterways during heavy rain, Rock Phosphate binds to soil particles and releases phosphorus gradually through microbial activity, root acid exudation, and natural mineral weathering.
Rock Phosphate is most effective in acidic soils with pH below 6.5. The lower pH environment helps dissolve the mineral matrix and liberate phosphorus into plant-available forms. In alkaline soils above 7.0, Rock Phosphate dissolves very slowly and may not provide adequate phosphorus in the first year. For alkaline soils, Bone Meal or Bone Char are better organic phosphorus choices because their phosphorus is already in more available forms.
Wicked Organics Rock Phosphate is OMRI-listed and ideal for building long-term phosphorus reserves in organic gardens, orchards, and perennial plantings. Apply 5-10 pounds per 100 square feet at planting or in fall, work into the top 6 inches, and let it release over multiple seasons. For new gardens and orchard plantings, a one-time heavy application of Rock Phosphate establishes a phosphorus bank that sustains plants for years with minimal replenishment.

Wicked Organics Rock Phosphate (0-12-0)

Bone Meal is the classic organic phosphorus source — steamed and ground animal bones providing 15% phosphorus, 3% nitrogen, and significant calcium (roughly 20-25% by weight). The calcium content makes Bone Meal a dual-purpose product: it supplies phosphorus for root and bloom development while contributing calcium that gently buffers soil acidity over time. It breaks down faster than Rock Phosphate, typically releasing nutrients over one growing season, making it better suited for annual crops and seasonal plantings where you need phosphorus available now rather than over multiple years.
Bone Char is a fundamentally different product despite its similar name. Bones are heated to very high temperatures in a low-oxygen environment — the same pyrolysis process used to make Bio Char — creating an activated carbon-phosphorus hybrid. The result provides both the phosphorus benefits of Bone Meal (at an even higher 16% concentration) and the soil-conditioning properties of Bio Char. The carbon structure creates micropore habitat for beneficial microbes while the phosphorus releases steadily through microbial activity.
Old Cobblers Farm carries both in the Wicked Organics line, and the choice between them depends on your goals. Use Bone Meal when you need phosphorus for the current season — at transplant time for tomatoes, in planting holes for bulbs, worked into beds for root crops. Use Bone Char when you want the dual benefit of phosphorus fertilization and permanent soil structure improvement — the carbon component persists for years, continuing to improve soil biology long after the phosphorus has been consumed.

Wicked Organics Kelp Meal (1-0-2)

Kelp Meal provides something no other amendment in the Old Cobblers Farm lineup can: natural plant growth hormones — cytokinins and auxins — that stimulate cell division, root branching, and lateral growth at concentrations far below what standard NPK analysis reveals. These growth regulators are the same compounds that synthetic plant growth regulators attempt to replicate, but in kelp they occur in naturally balanced ratios that plants have co-evolved with over millions of years of coastal ecosystem interaction.
Beyond growth hormones, kelp delivers over 60 trace minerals absorbed from ocean water during the seaweed's growth. Iron, zinc, manganese, boron, copper, molybdenum, cobalt — minerals commonly deficient in inland soils but essential for enzyme function, photosynthesis, and disease resistance. The NPK numbers are modest (1-0-2), but Kelp Meal's value lies entirely in what those numbers do not capture.
Use Kelp Meal as a supplement alongside your primary Old Cobblers Farm fertilizer program. It does not replace fertilizer — it makes fertilizer work better by filling micronutrient gaps and stimulating the root growth that allows plants to absorb nutrients more efficiently. Apply 1-2 pounds per 100 square feet mixed into soil at bed preparation, or brew kelp tea by steeping 1 cup per gallon of water for 24-48 hours and applying as a foliar spray or soil drench.

Wicked Organics Tea Seed Meal

Tea Seed Meal is unique in the Old Cobblers Farm lineup. Its primary value comes not from NPK numbers but from its 15-18% natural saponin content and over 50% organic matter. Saponins are plant-produced compounds with natural surfactant properties — they reduce surface tension in water, allowing moisture to penetrate compacted soil and hydrophobic (water-repellent) soil surfaces more effectively.
The granulated crumb form dissolves slowly after rainfall or irrigation, with each subsequent watering continuing to activate the granule and move saponin deeper into the soil profile. This extended-release delivery means a single application conditions soil biology over weeks rather than providing a one-time effect. The high organic matter content feeds soil microorganisms and improves soil structure through biological aggregation.
Apply Tea Seed Meal at 6-12 pounds per 1,000 square feet, broadcast evenly and watered in. It works in any soil type but provides the most dramatic improvement in compacted soils, clay soils with poor water infiltration, and soils that have developed hydrophobic layers from lack of organic matter.

Wicked Organics Epsom Salt (Magnesium Sulfate)
Epsom Salt delivers two critical secondary nutrients that are chronically deficient in New England soils: magnesium and sulfur. Magnesium is the central atom of every chlorophyll molecule — without adequate magnesium, photosynthesis slows and leaves develop characteristic interveinal chlorosis (yellowing between the veins while veins remain green). Sulfur is essential for amino acid synthesis, protein formation, and enzyme function.
Acidic soils in the northeast lose magnesium rapidly through leaching because acidic conditions release magnesium from soil particles and rainfall carries it below the root zone. This makes magnesium deficiency one of the most common nutrient problems in New England gardens — and one of the most easily corrected with Wicked Organics Magnesium Sulfate.
Old Cobblers Farm's Epsom Salt is food-grade quality and dissolves instantly in water for foliar sprays or soil drenches. For foliar application, dissolve 1-2 tablespoons per gallon and spray directly on leaves — magnesium absorbs through leaf tissue faster than through roots, making foliar feeding the quickest correction for visible deficiency symptoms. For soil application, broadcast 1-2 pounds per 100 square feet and water in. Epsom Salt does not significantly alter soil pH in either direction, making it safe to use in any growing situation without worrying about pH impacts.

Building a Complete Amendment Program
The most effective approach layers multiple Wicked Organics amendments for complementary benefits. A solid foundation program includes Greensand for potassium, trace minerals, and water retention; Bio Char for permanent microbial habitat and nutrient retention; Bone Meal or Rock Phosphate for phosphorus reserves; Kelp Meal for growth hormones and micronutrients; and Epsom Salt for magnesium and sulfur supplementation.
Apply amendments once or twice per year, typically in fall or early spring. Fall applications benefit from winter freeze-thaw cycles that integrate materials into the soil profile. Spring applications become available just as plants begin active growth. Let amendments work synergistically with your seasonal Wicked Growth or Wicked Organics fertilizer program — the amendments build the soil capacity, and the fertilizers deliver the seasonal nutrition.
Over 2-3 years of consistent amendment applications, you will notice soil that is darker in color, looser in texture, holds moisture noticeably longer between waterings, drains better after heavy rain, produces earthworms and visible fungal activity, and grows healthier plants with fewer pest and disease problems. These improvements compound over time — year three is better than year two, which was better than year one. The soil you build with amendments is the most valuable long-term asset in your garden.