Guaranteed Analysis
Nutrient Breakdown
N · Nitrogen8%
Provides a restrained 8% nitrogen (from urea) to support top growth without promoting excessive vine or leaf production at the expense of root and tuber development
P · Phosphorus16%
Delivers a strong 16% phosphorus (from diammonium phosphate) to drive deep root formation, tuber initiation, flower production, and overall below-ground development
K · Potassium16%
Supplies 16% potassium (from muriate of potash) to maximize tuber size, starch content, fruit firmness, skin quality, and storage life
Derived from: Urea, Diammonium Phosphate (DAP), Potassium Chloride (Muriate of Potash), Silicon Dioxide. Includes micronutrients.
Overview
What It Is
This 8-16-16 formula is the general-purpose version of Old Cobblers Farm's Seed Potato Fertilizer—both share the same Green Mountain Fertilizer formulation. The four-ingredient composition (urea, DAP, MOP, silicon dioxide with micros) delivers 40% combined NPK per pound, making it one of the most nutrient-dense formulas in the Wicked Growth lineup.
The 2:1 ratio of P+K to N is based on agronomic research showing that root crops, tuber crops, and fruiting crops perform best when phosphorus and potassium availability exceeds nitrogen. The DAP-based phosphorus helps adjacent phosphorus stay plant-available rather than becoming locked up. Micronutrients address boron, zinc, and manganese needs common in Northeast soils.
Crop Fit
Best For
PotatoesRoot VegetablesFlowering BulbsTransplantsNew PlantingsFruit TreesGarlicOnions
Ideal for any crop where root or tuber development is the primary goal. Potatoes, carrots, beets, turnips, parsnips, radishes, and garlic all thrive with the high P-K, low-N ratio. Flowering bulbs (tulips, daffodils, lilies) benefit from strong phosphorus and potassium for root establishment. New transplants of any kind benefit from high phosphorus for root recovery.
Application Rates
How Much to Use
| Garden & beds | 1-2 lbs per 100 sq ft incorporated into the soil before planting; 0.5 lbs per 100 sq ft as side-dress at mid-season |
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| Lawn | 3-5 lbs per 1,000 sq ft for new lawn establishment or phosphorus-deficient lawns (check local P restrictions) |
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| Trees & shrubs | 0.5-1 lb per inch of trunk diameter for fruit trees and ornamentals at planting |
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| Containers | 2 tablespoons per 5-gallon container, mixed into the bottom half of the soil at planting |
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| Frequency | 1-2 applications per season: primary at planting (incorporated into soil), optional side-dress mid-season for heavy-feeding crops |
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Step by Step
How to Apply
1Soil Test
Test soil to confirm phosphorus and potassium needs before applying this high-P, high-K formula.
2At Planting
At planting, incorporate 1–2 lbs per 100 sq ft into the top 6 inches of soil for root-zone placement.
3Row Crop Banding
For row crops, band fertilizer 2–3 inches below and to the side of seed or transplant for efficient uptake.
4Bulb Application
For bulbs, work into the planting bed before setting bulbs to provide phosphorus for root development.
5Water In
Water thoroughly after application to activate nutrients and settle soil.
6Optional Side-Dress
Optional mid-season side-dress at half rate for heavy-producing crops like tomatoes and peppers.
7Phosphorus Restrictions
Check local phosphorus restrictions before applying to lawns. Many municipalities limit P application on established turf.
This is primarily a planting-time fertilizer. Incorporate into the root zone before planting because phosphorus is immobile in soil. For garden beds, broadcast 1-2 lbs per 100 sq ft and till into the top 6 inches. For row crops, band 2-3 inches below and to the side of seed. For bulb plantings, work into the entire bed. For new tree and shrub plantings, mix into backfill soil. For commercial production, apply 400-800 lbs per acre based on soil tests. Apply using the same rates and methods as Old Cobblers Farm™ Seed Potato Fertilizer.
Handling & Timing
Safety & Season
Safety & Storage
Wear protective gloves and eye protection during handling. Avoid breathing dust. Wash hands thoroughly after handling. Store in a cool, dry, well-ventilated area. Slightly reactive with oxidizing agents, metals, alkalis, and moisture. Phosphorus runoff poses a threat to water quality—do not apply near waterways. Check local phosphorus fertilizer restrictions. Keep out of reach of children and pets.
Seasonal Notes
Spring: Primary application at planting for vegetables, root crops, and new plantings. Summer: Optional half-rate side-dress for heavy producers. Fall: Excellent for fall bulb plantings (tulips, daffodils, garlic). Winter: No application. Plan soil testing.
In Context
How It Compares
The 8-16-16 provides the high P-K ratio that root crops and bulbs need, which 10-10-10 cannot match. Compared to applying 0-46-0 and 0-0-60 separately, this is more convenient and includes nitrogen and micronutrients. The low nitrogen is safer for root crops than balanced fertilizers which deliver too much N. This is the same formulation as Old Cobblers Farm™ Seed Potato Fertilizer.
Answers
Frequently Asked Questions
What is 8-16-16 fertilizer used for?
8-16-16 fertilizer is a high-phosphorus, high-potassium blend with moderate nitrogen, designed for crops that need strong root development, heavy flowering, and superior fruit quality. It is especially popular for potatoes, root crops, bulbs, and fruiting vegetables where underground growth and reproductive performance matter most. The lower nitrogen prevents excessive vine or leaf growth that can steal energy from tuber and fruit formation. Old Cobblers Farm™ Wicked Growth 8-16-16 Multi-Purpose Fertilizer provides a versatile, productivity-focused nutrient profile for gardens, farms, and landscape plantings.
Is 8-16-16 good for potatoes?
Yes, 8-16-16 is one of the best fertilizer ratios for potatoes. The high phosphorus (16%) promotes strong root systems and tuber initiation, while the high potassium (16%) improves tuber size, density, skin quality, and storage life. The moderate nitrogen (8%) supports healthy foliage without encouraging excessive vine growth at the expense of tuber production. Apply at planting and side-dress at mid-season when tubers are actively forming. Old Cobblers Farm™ Wicked Growth Seed Potato Fertilizer uses this proven 8-16-16 formula to deliver the precise nutrient balance potatoes need for maximum yield and quality.
What is the best fertilizer for root crops?
Root crops like potatoes, carrots, beets, and turnips perform best with fertilizers that emphasize phosphorus and potassium over nitrogen. Ratios like 8-16-16 or 5-10-10 provide the underground nutrition these crops need without promoting excessive top growth. Phosphorus drives root and tuber development, while potassium improves size, flavor, and storage quality. Too much nitrogen causes root crops to produce lush foliage with small, misshapen roots. Old Cobblers Farm™ Wicked Growth 8-16-16 Multi-Purpose Fertilizer is specifically suited for root crops, delivering the high P-K nutrition they demand.
How much 8-16-16 fertilizer do potatoes need?
For potatoes, apply 2–3 pounds of 8-16-16 per 100 square feet during soil preparation, mixing into the top 6 inches before planting seed potatoes. Side-dress with 1–2 pounds per 100 feet of row after plants emerge and again at mid-season when tubers are forming. For container potatoes, add 1 tablespoon per gallon of soil at planting and reapply every 4–6 weeks. Avoid piling fertilizer directly against seed pieces, as concentrated contact can cause burn. Old Cobblers Farm™ Wicked Growth Seed Potato Fertilizer 8-16-16 provides potatoes with the targeted nutrition they need at every growth stage.
What is the difference between 8-16-16 and 10-10-10 fertilizer?
The key difference is nutrient emphasis. 10-10-10 provides equal, balanced nutrition suitable for general gardening, while 8-16-16 shifts the balance heavily toward phosphorus and potassium for crops that prioritize root growth, flowering, and fruiting over leafy vegetative growth. Use 10-10-10 for mixed gardens and all-purpose feeding. Use 8-16-16 for potatoes, root vegetables, bulbs, and any crop where you want to maximize production below ground or in fruit. Old Cobblers Farm™ offers both formulas so you can match the fertilizer to the specific crop demands in your garden.
Can I use 8-16-16 on my flower garden?
Yes, 8-16-16 is excellent for flower gardens, particularly for flowering plants that need strong root systems and prolific bloom production. The high phosphorus fuels abundant flower bud formation, while the potassium improves bloom color, longevity, and stem strength. It is especially effective for dahlias, peonies, roses, zinnias, and other heavy-blooming species. Apply at bed preparation and side-dress during the blooming season. Old Cobblers Farm™ Wicked Growth 8-16-16 Multi-Purpose Fertilizer helps flower gardens produce more blooms with richer color and longer vase life.
Is 8-16-16 good for carrots and beets?
Yes, 8-16-16 is a strong choice for carrots, beets, turnips, parsnips, and other root vegetables. These crops need phosphorus for root elongation and cell division below ground, and potassium for root density, flavor development, and disease resistance. The moderate nitrogen supports just enough top growth to fuel photosynthesis without diverting energy from root production. Apply before planting and side-dress once during the growing season. Old Cobblers Farm™ Wicked Growth 8-16-16 Multi-Purpose Fertilizer delivers the high P-K nutrition that root crops require for larger, healthier, more flavorful harvests.
