10-20-20 fertilizer is a general purpose fertilizer that is best used in gardens for vegetable plants. It is especially good for beans and root vegetables. 10-20-20 is not well-suited for use on lawns because it does not contain an ideal nutrient balance for established grass or new grass seedlings. For lawns, use a specialized fertilizer instead of 10-20-20.
What Do the Numbers on 10-20-20 Fertilizer Mean?
The 3 numbers in 10-20-20 fertilizer indicate the percentage of nitrogen, phosphorus, and potassium in that order. This means that one bag of 10-20-20 contains 10% nitrogen, 20% phosphorus, and 20% potassium, by weight.
- First Number: Indicates the percentage of nitrogen in the fertilizer.
- Second Number: Indicates the percentage of phosphorus in the fertilizer.
- Third Number: Indicates the percentage of potassium in the fertilizer.
A 10-pound bag of 10-20-20 fertilizer thus contains 1 pound of nitrogen, 2 pounds of phosphorus, and 2 pounds of potassium. These primary nutrients are required for plant life. In the right balance, these nutrients will drive plant growth of specific varieties.
What is the Best Use for 10-20-20 Fertilizer?
Because 10-20-20 fertilizer is relatively low in nitrogen and high in both phosphorus and potassium, it is best suited for growing legumes (beans) and root vegetables. Beans, including soybeans, green beans, and runner beans thrive off high-phosphorus fertilizer. Root vegetables, such as potatoes, yams, and turnips, require potassium to form their starchy, edible roots.
- Use 10-20-20 in a garden plot where you grow green beans, runner beans, and lima beans.
- 10-20-20 is good fertilizer for root vegetables. Add it to soil where you grow sweet potatoes, carrots, and radishes.
- 10-20-20 is not ideal for flowering ornamentals, which have higher nitrogen needs.
Although 10-20-20 can be used with some success for boosting the growth of berries, a balanced 12-12-12 fertilizer is better suited. If you are fertilizing flowers, avoid 10-20-20. Flowers require high nitrogen and potassium fertilizers with low phosphorus. 16-4-8 is a better choice for flowers.
Why is 10-20-20 Fertilizer Not Good for Lawns?
Grass is a nitrogen-hungry plant and 10-20-20 simply doesn’t deliver enough nitrogen. Mature grass needs high-nitrogen fertilizer with little-to-no phosphorus and some potassium. It’s not uncommon to see fertilizers for established lawns with nutrient balances such as 32-0-4. In some cases, an overload of phosphorus can even be damaging to grass. Don’t use 10-20-20 on your established lawn.
- 10-20-20 fertilizer is low in nitrogen and high in phosphorus and potassium.
- Mature lawns need high nitrogen fertilizers with low amounts of phosphorus and potassium for best growth.
- New sod and newly seeded lawns need a fertilizer that is high in nitrogen and phosphorus, with very little potassium.
- 10-20-20 is not suited for new or established grass.
A new lawn grown from seed or sod has specialized needs. The grass needs phosphorus for root growth and nitrogen to trigger the blades and stalks to form. However, new grass doesn’t need the high potassium content found in 10-20-20. A good lawn starter will have a formula such as 22-23-4. 10-20-20 simply isn’t a good fertilizer for grass at any stage.
When Should You Use 10-20-20 Fertilizer?
Till 10-20-20 fertilizer into your garden plot in spring before planting annual legumes and root vegetables. By tilling in this fertilizer, you will set the stage for your beans and tubers to get a great head start and feed them throughout their growth cycle. Mixing 10-20-20 into the top 6 inches (15 cm) of soil is a great way to prepare an annual garden plot for success.
- Spring is the best time to add 10-20-20 to a garden plot where you plan to plant legumes and/or root vegetables.
- Till 10-20-20 into the soil at a depth of 6 inches (15 cm) if you have not yet planted the plot.
- If you are already growing plants in your garden, spread 2–3 pounds of 10-20-20 for every 100 square feet. Then, water in the fertilizer.
If you are fertilizing a plot where garden plants are already established, spread 10-20-20 fertilizer evenly over the area to be fertilized. 2–3 pounds of 10-20-20 is enough to fertilize 100 square feet of beans or berries. A single application of fertilizer in spring will fuel your plants’ growth into summer.
What Kind of Fertilizer is 10-20-20?
10-20-20 is a high phosphorus, high potassium fertilizer with relatively little nitrogen. This makes 10-20-20 a good fertilizer for beans and tubers, but not an ideal fertilizer for flowers or grass. To use 10-20-20 fertilizer, till into your garden soil, or spread it on the soil surface in spring. If you are looking for a lawn fertilizer, search for a product with high nitrogen content. Similarly, flowers require a higher nitrogen content than 10-20-20 offers. Using 10-20-20 on your lawn will not yield good results and the high phosphorus levels can even harm some mature grasses.