Asparagus has gained popularity in the home garden due to its many health benefits, including its ability to lower blood pressure, fight inflammation, and improve digestive health. This easy-to-grow vegetable is a perennial that returns every year. Although it takes a year or two to become established, it keeps producing for years. Knowing how and when to fertilize your asparagus will ensure a healthy crop for years.
Does asparagus need fertilizer to grow well?
Like all plants, asparagus needs water, sunlight, and adequate nutrients to grow. If your asparagus grows in fertile soil, or you amend it regularly with compost or well-rotted manure, it may not need additional fertilizer. However, it is generally recommended that you apply fertilizer to your asparagus soil twice a year. Once in the early spring before the first shoots emerge and again after your last harvest of the year.
This is especially important in the first few years until your asparagus bed is fully established. There are two ways to determine if your asparagus bed needs additional fertilizer.
- Observe its growth. If the asparagus is robust and healthy, it is likely getting the nutrients it needs and may not need to be fertilized frequently. Weak or slow growth may indicate a lack of nutrients in the soil.
- Do a soil test in the fall. This will alert you to any deficiencies in your soil. A written summary or report will provide recommendations for improving the soil and adding nutrients.
Can you do a soil test yourself?
There are many home soil tests available that measure the soil pH and the nitrogen, phosphorus, and potassium levels in your soil, but you should think of home soil tests as a quick measure of the health of your soil. They are not as precise as a professional soil test and only provide cursory recommendations for correcting the soil.
A soil testing service will provide you with a detailed assessment of your soil and recommendations for correcting it. Many University Extension Offices provide soil testing for a nominal fee. It is recommended that you do a thorough soil test every 3 to 5 years as the soil can change over time.
What is an NPK ratio?
NPK stands for nitrogen, phosphate, and potassium; the three vital nutrients plants need to grow. Every fertilizer has an NPK ratio denoted as a series of three numbers separated by dashes. These numbers tell the formula’s percentage of nitrogen, potassium, and phosphate. For example, a fertilizer with an NPK ratio of 5-10-10 contains 5 percent nitrogen, 10 percent phosphate, and 10 percent potassium.
What NPK ratio does asparagus need?
Opinions vary on the best NPK ratio for asparagus. While several sources, such as Backyard Vegetable Gardening and Hobby Farms, recommend a formula high in phosphate (P) and potassium (K), other sources, such as Iowa State University Extension, report that you should use a balanced formula, such as 10-10-10 on your asparagus.
The NPK ratio can be found on the bags of fertilizer in the form of three numbers (such as 5-10-10 or 10-10-10). This represents the percentage of Nitrogen (N), phosphate (P), and potassium (K) in the formula.
A balanced fertilizer contains approximately the same percentage of all three nutrients. A formula high in phosphate and potassium should have higher numbers in the last two places. For example, a formula of 5-10-10 or 8-24-24 is high in phosphate and potassium, while a formula of 10-10-10 is balanced.
Why does asparagus need fertilizer higher in P+K?
Phosphorus and potassium both support healthy plant growth. Phosphorus promotes a healthy root system, helps make seeds and flowers, and helps plants fight disease. Potassium helps build strong stems, promotes rapid growth, and also helps prevent diseases.
Using fertilizer high in phosphorus and potassium helps your asparagus develop strong roots and stems. Because you eat the stems of the asparagus, healthy stem development is essential.
How do I know how much fertilizer to add?
As a rule, you should follow the application rate on the package. This is typically given in amount per area. For example, 10-10-10 fertilizer is applied at a rate of 1 to 1 ½ pounds per 100 square feet. AgriLife recommends about ½ cup of fertilizer per 10 feet for applying fertilizer to rows in the garden. If you are not sure how much asparagus to grow per person read this article.
Taking a soil test in the fall will tell you what nutrients your soil needs. Follow the soil test report’s recommendations for soil amendments and fertilizer application.
How much fertilizer should I add if I don’t do a soil test?
In the absence of a soil test, you should follow the application rate on the container of fertilizer. For example, apply 10-10-10 fertilizer at a rate of 1 to ½ pounds per 100 square feet or approximately ½ cup per 10 feet of row.
When should I add the fertilizer?
Fertilize your asparagus early in the spring before new spears emerge and again in early to mid-summer when you have harvested your last crop of asparagus. This is vital for newly planted asparagus plants. After the third year, your asparagus may not need fertilizing twice a year, depending on the condition of your soil and whether you mulch it regularly with compost or rotted manure.
Examples of fertilizer suitable for asparagus
The type of fertilizer you use for your asparagus depends on what nutrients your soil needs. Whether you choose a liquid fertilizer, traditional granular fertilizer, or a time-release formula is a matter of personal preference.
- Liquid Fertilizer: This type of fertilizer is mixed with water and applied to either the plant or the soil. It is quick and easy to apply. Miracle-Gro All Purpose Plant Food is a good choice in liquid fertilizer.
- Time Release: Time-released formulas release nutrients gradually over time, helping to provide a steady source of the nutrients your asparagus needs to thrive. Osmocote for Flowers and Vegetables is a good choice. Garden Tone is an organic option that is sprinkled on the soil and watered to dissolve it into the soil.
- Granular Fertilizer: This fertilizer is mixed into the soil to provide nutrients. Burpee All Purpose makes a good choice for an all-purpose balanced fertilizer.
The type of fertilizer and the timing of its application best for asparagus depends on the condition of your soil and the health of your asparagus. As a rule, asparagus should be fertilized in the spring before the new shoots appear and again after your last harvest of the year. While newly planted asparagus beds will benefit from this routine, established beds may not need fertilizing every year. Testing your soil is the best way to determine the correct formula and application schedule for your asparagus.