Best High-Phosphorus Multi-Purpose Fertilizer (8-16-16): Double P & K for Root Crops, Tubers & Heavy Producers Buy on Old Cobblers Farm
When your garden demands more phosphorus and potassium than nitrogen, 8-16-16 delivers. Double the P and K relative to N makes this the formula for root crops, tuber development, and any planting where underground growth matters most.
Old Cobblers Farm™ Wicked Growth 8-16-16 Fertilizer – Multi Purpose
by Conventional Fertilizer — Littleton, NH
Double P & K Ratio
16% phosphorus and 16% potassium — double the nitrogen percentage. This ratio prioritizes root development, tuber sizing, and storage quality over leafy vegetative growth.
Slow-Release Granular
Nutrients release gradually over weeks, preventing burn on young plants and reducing the need for frequent reapplication. One application carries through critical growth windows.
Maximum P & K Per Bag
0.8 lbs actual P₂O₅ and 0.8 lbs actual K₂O per 5 lb bag. The highest combined phosphorus and potassium delivery of any Wicked Growth commercial blend.
Root Crop Specialist
Potatoes, carrots, beets, turnips, parsnips, and radishes all thrive on high P & K with moderate nitrogen. This formula matches their nutritional profile exactly.
170–250 sq ft Per Bag
5 lbs covers a standard garden bed at broadcast rate. Apply at planting and side-dress mid-season for two-phase feeding.
Bulb & Transplant Friendly
High phosphorus supports root establishment in transplants and builds energy reserves in fall-planted bulbs heading into winter dormancy.
Multi-Purpose Beyond Root Crops
Also excellent for flowering shrubs, new tree plantings, and any crop where root establishment and fruit quality matter more than foliage growth.
Trusted by 20,000+ Growers
Developed in Littleton, New Hampshire. Sold nationwide on Amazon, Walmart, eBay, and theoldcobblersfarm.com.
| NPK Ratio | 8-16-16 |
| Item Form | Slow-release granular |
| Coverage | 170–250 sq ft per 5 lb bag |
| Category | Conventional Fertilizer |
| Type | All-Purpose NPK Blends |
| Sizes | 5 lb | 10 lb | 15 lb | 20 lb |
| NPK | 8-16-16 |
| Nitrogen | 8% |
| Phosphorus | 16% available phosphate |
| Potassium | 16% soluble potash |
| Secondary | Magnesium, Micronutrients |
| Form | Slow-release granular |
| Rate | 2–3 lbs / 100 sq ft |
| Method | Broadcast or side-dress |
| Sizes | 5, 10, 15, 20 lb bags |
| Best For | Root crops, tubers, bulbs, transplants, multi-purpose |
| Feature | Old Cobblers Farm™ Wicked Growth 8-16-16 Fertilizer – Multi Purpose Old Cobblers Farm | TomatoGain 8-16-16 BGI Fertilizers | Morcrop Tomato & Vegetable Food Lilly Miller (Pennington) | 5-10-10 Tomato & Vegetable Fertilizer CZ Garden Organics | Vegetable & Tomato Granular Plant Food Jobe's Organics | Tomato-Tone Organic Espoma | Select Organics Potato Fertilizer Winchester Gardens | Potatoes Alive!™ Fertilizer Gardens Alive! / Gurney's |
|---|---|---|---|---|---|---|---|---|
| NPK | 8-16-16 | 8-16-16 | 5-10-10 | 5-10-10 | 2-5-3 | 3-4-6 | 6-3-9 | 3-4-3 |
| Form | Slow-release granular | — | — | — | — | — | — | — |
| Coverage | 170–250 sq ft per 5 lb bag | Not listed | Not listed | Not listed | Not listed | Not listed | Not listed | Not listed |
| Price / Size | 5 lb | 10 lb | 15 lb | 20 lb | $9–$14 | $10–$22 | $14–$25 | $8–$23 | $8–$28 | $13–$18 | $12–$13 |
| Our Take | The highest combined P & K formula in the Wicked Growth commercial ... | — | — | — | — | — | — | — |
TomatoGain 8-16-16
Morcrop Tomato & Vegetable Food
5-10-10 Tomato & Vegetable Fertilizer
Vegetable & Tomato Granular Plant Food
Tomato-Tone Organic
Select Organics Potato Fertilizer
Potatoes Alive!™ Fertilizer
Double P & K Ratio
16% phosphorus and 16% potassium — double the nitrogen percentage. This ratio prioritizes root development, tuber sizing, and storage quality over leafy vegetative growth.
Slow-Release Granular
Nutrients release gradually over weeks, preventing burn on young plants and reducing the need for frequent reapplication. One application carries through critical growth windows.
Maximum P & K Per Bag
0.8 lbs actual P₂O₅ and 0.8 lbs actual K₂O per 5 lb bag. The highest combined phosphorus and potassium delivery of any Wicked Growth commercial blend.
Root Crop Specialist
Potatoes, carrots, beets, turnips, parsnips, and radishes all thrive on high P & K with moderate nitrogen. This formula matches their nutritional profile exactly.
