Organic additives without guesswork.
Use compost, minerals, meals, biology, oils, soaps, and pest controls with a purpose. The rule is simple: match the additive to the problem, the plant, and the soil.
Do not stack amendments blindly.
For outdoor beds, test soil before repeated mineral or pH amendments. For containers, refresh old mix and feed lightly during active growth instead of trying to fix every symptom with one product.
Additive guide
Search by product, purpose, plant need, pest, nutrient, or caution. Buy buttons are Amazon affiliate links; verify the current label, ingredients, seller, and price before purchasing.
| Additive | Best use | How to use | Caution | Buy |
|---|---|---|---|---|
| Finished compost Soil builder |
All-purpose organic matter, soil biology, and slow nutrient support. | Top-dress containers lightly or mix into garden beds before planting. | Use fully finished compost only. Unfinished compost can heat, smell, or tie up nitrogen. | |
| Worm castings Soil builder |
Gentle microbe-rich amendment for seedlings, houseplants, herbs, and containers. | Use as a light top-dress or small portion of potting mix. | Too much can make mixes dense and wet, especially indoors. | |
| Leaf mold Soil builder |
Improves moisture holding, tilth, fungal biology, and woodland-style beds. | Use as mulch, bed amendment, or a small part of seed-starting mixes when screened. | Low in nutrients. Do not use sour or anaerobic material in pots. | - |
| Aged manure Nutrient |
Outdoor vegetable beds, compost piles, and hungry annual crops. | Use well-aged or composted manure before planting season. | Fresh manure can burn roots and may carry pathogens. Avoid on harvest-ready leafy crops. | |
| Green manure / cover crop residue Soil builder |
Building biomass, protecting beds, feeding soil life, and reducing erosion. | Chop before heavy seed set and leave as mulch or compost into beds ahead of planting. | Allow breakdown time before seeding small crops. Some covers can regrow or seed. | - |
| Bokashi compost Compost input |
Fermenting kitchen scraps before composting or trench burial. | Bury fermented material in soil or finish it in a compost system before planting into it. | Too acidic and active for direct contact with roots until finished. | - |
| Compost tea Biology |
Short-term microbial inoculation for living soil systems. | Use fresh, clean, well-aerated tea as a soil drench. | Quality varies. Avoid spraying edible leaves close to harvest. | - |
| Biochar Soil structure |
Long-term nutrient holding, drainage balance, and habitat for microbes. | Charge with compost, castings, or fertilizer before mixing into soil. | Uncharged char can temporarily hold nutrients away from plants. | |
| Humic acid / fulvic acid Soil support |
Improving nutrient exchange and root-zone chemistry in depleted media. | Apply at label rate as a drench or mixed into soil products. | Not fertilizer by itself. Avoid treating it as a cure-all. | |
| Coconut coir Potting structure |
Peat alternative for moisture retention in potting mixes. | Rinse and buffer if needed, then blend with aeration and nutrients. | Can be high in salts or potassium. It contains little nutrition. | |
| Sphagnum peat moss Potting structure |
Acidic moisture retention for seed starting and acid-loving plants. | Pre-moisten thoroughly and blend with perlite, bark, compost, or fertilizer. | Hydrophobic when dry and acidic. Sustainability concerns vary by source. | |
| Pine bark fines Potting structure |
Airy container mixes, aroids, orchids, citrus, blueberries, and woody plants. | Blend into potting media for drainage, structure, and mild acidity. | Fresh bark can tie up nitrogen. Use aged or composted bark for sensitive mixes. | - |
| Perlite Aeration |
Improving drainage and oxygen in seedling, houseplant, and vegetable mixes. | Blend into potting soil, especially for containers that stay wet. | Dust is irritating. Wet before handling and avoid inhaling dust. | |
| Pumice Aeration |
Long-lasting drainage for succulents, cactus, bonsai, and heavy containers. | Blend into potting mixes or use as part of a gritty mix. | Heavy in large pots. It adds structure, not nutrients. | - |
| Vermiculite Moisture holding |
Seed starting, cuttings, and crops that like steady moisture. | Use lightly in mixes where water retention is needed. | Can keep soil too wet for succulents or plants prone to root rot. | |
| Rice hulls Aeration |
Lightweight aeration and short-term structure in organic potting mixes. | Blend into container media as a renewable perlite alternative. | Breaks down over time. Use parboiled hulls to reduce weed risk. | |
| Coarse horticultural sand Drainage |
Gritty mixes for succulents, cactus, herbs, and Mediterranean plants. | Use coarse washed sand only, blended with organic matter and aeration. | Fine sand can compact and worsen drainage. | |
| Horticultural charcoal Potting support |
Orchid, terrarium, and aroid mixes where odor control and structure help. | Use small amounts in chunky mixes. | Not the same as fertilizer. Avoid grilling charcoal or treated charcoal. | |
| Blood meal Nitrogen |
Fast organic nitrogen for leafy greens and nitrogen-hungry outdoor crops. | Mix lightly into soil before planting or side-dress at label rate. | Can burn or push weak leafy growth if overused. May attract animals. | |
| Feather meal Nitrogen |
Slower nitrogen release for beds and long-season crops. | Mix into soil before planting so microbes can begin breaking it down. | Not useful for an instant correction. Needs warm active soil biology. | |
| Fish emulsion Quick feed |
Quick organic nitrogen boost during active growth. | Dilute strongly and water into moist soil. | Can smell and can overfeed soft growth. Avoid overuse indoors. | |
| Fish hydrolysate Balanced feed |
Gentle feeding for vegetables, herbs, seedlings, and stressed plants. | Dilute at label rate and apply as a soil drench during active growth. | Odor varies. Store well and do not exceed label rates. | |
| Fish meal Slow feed |
Slow organic nitrogen and phosphorus in beds and containers. | Mix into soil before planting or use in balanced organic blends. | Can attract animals. Avoid heavy use in small indoor pots. | |
| Alfalfa meal / pellets Growth support |
Mild nitrogen, potassium, and growth support for roses, vegetables, and compost. | Scratch lightly into beds or soak pellets for a mild drench. | Can heat if piled thickly. Use modest amounts around containers. | - |
| Soybean meal Nitrogen |
Slow organic nitrogen for garden beds and heavy feeders. | Mix into soil before planting or use in organic fertilizer blends. | Can attract pests or animals. Needs microbial breakdown. | - |
| Cottonseed meal Acid feed |
Slow nitrogen for acid-loving plants like blueberries and azaleas. | Apply to outdoor soil at label rate and water in. | Not ideal for already acidic soil unless nutrients are needed. | - |
| Kelp meal / liquid seaweed Trace support |
Trace minerals, stress support, and mild potassium. | Use kelp meal in soil or liquid seaweed as a diluted drench or foliar spray. | Not a complete fertilizer by itself. | |
| Bone meal Phosphorus |
Slow phosphorus and calcium for bulbs, roots, and flowering crops when soil needs it. | Mix into the root zone before planting, especially outdoors. | Excess phosphorus can lock out iron and zinc. Use soil-test context. | - |
| Fish bone meal Phosphorus |
Organic phosphorus and calcium for fruiting crops and transplant mixes. | Blend into soil before planting or use in balanced organic fertilizer. | Slow acting. Avoid repeated use without knowing phosphorus levels. | |
| Rock phosphate Phosphorus |
Long-term phosphorus support in acidic outdoor soils. | Apply based on soil test and mix into beds before planting. | Very slow in neutral or alkaline soils. Do not use as a quick fix. | |
| Seabird guano Fast nutrients |
Concentrated organic nitrogen or phosphorus depending on product analysis. | Use sparingly at label rate in outdoor beds or compost blends. | Can burn roots and may have sustainability concerns. | |
| Bat guano Fast nutrients |
Concentrated organic nutrient source for specialized growers. | Use tiny amounts, usually mixed into soil or compost teas. | Overuse burns plants. Sourcing and dust safety matter. | |
| Crab meal / shrimp meal Calcium + biology |
Calcium, nitrogen, chitin, and soil biology support. | Mix into beds before planting or add to compost in small amounts. | Can attract animals and may affect shellfish-allergic handlers. | |
| Neem seed meal / neem cake Soil + pest pressure |
Slow nitrogen and soil pest suppression support in living soil. | Mix lightly into soil or top-dress and water in. | Too much can stress seedlings. Keep away from pets that chew soil. | |
| Langbeinite / sulfate of potash-magnesia K + Mg |
Potassium, magnesium, and sulfur for fruiting crops and deficiencies. | Apply by soil test or clear need, then water in. | Do not stack with Epsom salt or high-potassium products blindly. | |
| Greensand Trace minerals |
Very slow potassium and trace minerals in outdoor soil. | Mix into beds as a long-term amendment. | Too slow for urgent potassium problems. | - |
| Gypsum Calcium + sulfur |
Adds calcium and sulfur without raising pH much. | Use where calcium is low and pH is already acceptable. | Not a universal blossom-end rot cure. Watering swings are often the cause. | |
| Dolomitic lime Raise pH |
Raises acidic soil pH while adding calcium and magnesium. | Apply according to soil test, then mix into outdoor beds or potting mix before planting. | Bad fit for acid-loving plants or alkaline soil. | |
| Calcitic lime Raise pH |
Raises pH and adds calcium without much magnesium. | Use when soil is acidic but magnesium is already sufficient. | Over-liming locks out iron, manganese, and other micronutrients. | |
| Elemental sulfur Lower pH |
Long-term pH lowering for blueberries and acid-loving outdoor beds. | Apply months ahead of planting and retest soil. | Acts slowly and can burn if overused. Do not guess rates. | |
| Epsom salt Magnesium |
Magnesium sulfate for likely magnesium deficiency. | Use lightly as a drench only when symptoms and context fit. | Not a universal green-up cure. Excess magnesium can disrupt calcium and potassium balance. | - |
| Oyster shell flour Calcium |
Slow calcium and mild pH support in acidic soils. | Mix into beds or compost at label rate. | Raises pH over time. Avoid around acid-loving plants unless testing supports it. | - |
| Aragonite Calcium |
Calcium carbonate source for acidic soils and calcium-demanding crops. | Apply based on soil pH and calcium need. | Can raise pH. Not for already alkaline soil. | - |
| Basalt rock dust Trace minerals |
Slow-release trace mineral support in long-term soil building. | Blend into compost or outdoor beds in modest amounts. | Not a fast fertilizer. Dust control matters when handling. | |
| Azomite / mineral rock dust Trace minerals |
Broad trace mineral addition for depleted soils or compost blends. | Use sparingly and evenly mixed into soil or compost. | Not a substitute for balanced fertility. Avoid over-application. | |
| Zeolite Nutrient holding |
Improves cation exchange and nutrient holding in sandy or container mixes. | Blend a small amount into potting soil or raised bed mixes. | Too much can make media heavy. It supplies little nutrition itself. | |
| Mycorrhizal inoculant Biology |
Root partnership support at transplanting for many vegetables, fruits, and ornamentals. | Place directly on roots or in the planting hole. | Works best with compatible plants. Brassicas generally do not form mycorrhizal partnerships. | |
| Beneficial bacteria inoculant Biology |
Seedling, transplant, compost, and living-soil microbial support. | Apply at label rate as a root dip, seed treatment, or soil drench. | Needs living conditions: moisture, organic matter, and reasonable temperatures. | |
| Beneficial nematodes Soil pests |
Biological support for fungus gnat larvae, grubs, thrips pupae, and some soil pests. | Apply fresh to moist soil, then keep soil evenly moist for establishment. | Species matters. Heat, sun, and dry soil can kill them quickly. | - |
| Unsulfured molasses Microbe feed |
Feeding microbes in compost tea or active compost systems. | Use tiny amounts in aerated compost tea or compost recipes. | Can create anaerobic stink or attract pests if poured into pots heavily. | |
| Neem oil Pest tool |
Low-toxicity pest management for some soft-bodied pests and mites. | Spray in shade or evening, covering leaf undersides, and repeat as needed. | Can damage stressed plants. Avoid heat, intense light, and open pollinator blooms. | - |
| Insecticidal soap Pest tool |
Contact control for aphids, mites, whiteflies, and mealybugs. | Spray direct contact on pests, especially undersides and stems. | No residual control. Test sensitive plants and repeat treatment is usually required. | |
| Horticultural oil Pest tool |
Smothering scale, mites, aphids, and overwintering pest eggs. | Use refined horticultural oil at label rate with thorough coverage. | Avoid heat, drought-stressed plants, and plants listed as oil-sensitive. | |
| Dormant oil Woody pest tool |
Overwintering scale, mites, and eggs on dormant fruit trees or ornamentals. | Apply during dormancy under label temperature conditions. | Can injure leafed-out or stressed plants. Follow label timing closely. | |
| BTI Larvae control |
Fungus gnat larvae in houseplant soil and mosquito larvae in water. | Use mosquito bits or dunks as a soil drench according to label. | Does not kill adult gnats. Pair with drying soil surface and sticky traps. | - |
| BTK Caterpillars |
Organic control for leaf-eating caterpillars on vegetables and ornamentals. | Spray leaves where caterpillars feed, repeating after rain as label allows. | Targets caterpillars, including butterfly larvae. Use only where needed. | - |
| Spinosad Pest tool |
Thrips, caterpillars, leaf miners, and some beetle larvae. | Apply at label rate in evening after pollinators are inactive. | Can harm bees while wet. Do not spray open blooms. | |
| Pyrethrin Knockdown spray |
Fast knockdown for visible pests when gentler tools are not enough. | Use targeted spot applications at label rate. | Broad-spectrum. Can harm beneficial insects and pollinators. | - |
| Diatomaceous earth Dry pest barrier |
Crawling insects in dry cracks, greenhouse benches, and limited soil-surface use. | Apply a very light dry dusting where pests travel. | Ineffective when wet. Dust irritates lungs and can harm beneficial insects. | |
| Kaolin clay Protective barrier |
Sunscald reduction and pest deterrence on fruit trees and some vegetables. | Spray as a fine white film before pest pressure or heat stress. | Residue must be washed from harvests. Reapply after heavy rain. | - |
| Copper fungicide Disease tool |
Preventive organic-approved tool for some bacterial and fungal diseases. | Apply before or early in disease pressure, following crop label directions. | Copper accumulates in soil and can injure plants. Use sparingly. | - |
| Sulfur fungicide Disease + mites |
Powdery mildew, some fungal issues, and mite suppression on tolerant plants. | Apply at label rate when temperatures are moderate. | Do not use with oils or in hot weather. Some plants are sulfur-sensitive. | |
| Potassium bicarbonate Mildew tool |
Powdery mildew suppression on many ornamentals and edibles. | Use labeled products with good leaf coverage. | Can burn leaves if mixed too strong. It manages disease; it does not fix airflow. | - |
| Iron phosphate slug bait Slug control |
Organic slug and snail control around seedlings, hostas, strawberries, and greens. | Scatter lightly according to label after watering or rain. | Use labeled products only and keep away from children and pets. | |
| Corn gluten meal Pre-emergent |
Organic pre-emergent weed suppression in established beds and lawns. | Apply before weed seeds germinate and water in as directed. | Prevents desired seeds too. It is not useful after weeds are growing. | - |
| Horticultural vinegar Weed burn-down |
Top-killing small annual weeds in cracks or non-crop areas. | Use carefully as a spot treatment on dry sunny days. | Nonselective and acidic. Can burn skin, eyes, crops, and soil life. | - |
| Organic potting mix Potting structure |
Container resets, seedling upgrades, and mixes that combine compost, biochar, aeration, or peat-free structure. | Use as a base mix, then adjust drainage and nutrition to the plant. | Bagged mixes vary. Check ingredients, moisture, salt content, and whether fertilizer is already included. | |
| Seed-starting mix Seed starting |
Germinating seeds and starting tender seedlings in trays or small pots. | Pre-moisten, fill cells loosely, and avoid heavy fertilizer until seedlings are established. | Too-rich or dense mixes can cause damping off, gnats, or poor root growth. | |
| All-purpose organic fertilizer blend Balanced feed |
General vegetable, herb, flower, and container feeding when a broad nutrient blend is appropriate. | Apply at label rate during active growth and water in well. | Do not layer multiple complete fertilizers together. Excess salts and nutrients can burn roots. | |
| Bloom fertilizer blend Flowering support |
Flowering and fruiting crops when phosphorus and potassium support are needed. | Use during bud, bloom, or fruiting stages according to the product label. | Avoid bloom boosters in already high-phosphorus soil. | |
| Grow fertilizer blend Vegetative support |
Leafy growth, transplants, and plants recovering into active growth. | Feed lightly during active growth and reduce when growth slows. | Too much nitrogen can create soft growth and pest-prone foliage. | |
| Vegetable and herb fertilizer blend Edible crops |
Herbs, greens, tomatoes, peppers, and raised-bed food gardens. | Match the label rate to crop stage and container or bed size. | Edible-crop labels matter. Confirm harvest timing and application directions. | |
| Legume inoculant Biology |
Beans, peas, soybeans, cover crops, and legumes that benefit from compatible nitrogen-fixing bacteria. | Coat seed or apply at planting according to the inoculant label. | Crop compatibility matters. Inoculant species are not universal. | |
| Plant oil 3-in-1 spray Pest + disease |
Soft-bodied pests, mites, and some leaf disease pressure when a labeled botanical oil spray fits the plant. | Spray in shade or evening with complete coverage, then repeat only as the label allows. | Oil-based sprays can burn stressed plants or leaves in heat and bright sun. | |
| Botanical disease control spray Disease tool |
Powdery mildew, black spot, blight, and similar foliar disease pressure where the label supports use. | Apply early with good coverage and pair with airflow, spacing, and dry foliage habits. | Sprays suppress disease; they do not fix crowding, humidity, or chronic wet leaves. | |
| Potassium sulfate Potassium |
Potassium support where soil tests or crop needs justify extra potassium without added nitrogen. | Apply sparingly and water in, or use solution-grade products only as directed. | Too much potassium can interfere with magnesium and calcium balance. |