When To Fertilize Asparagus

Knowing when to fertilize asparagus is the single most important thing you can do for a healthy, productive bed. This perennial crop has unique needs, and timing your feedings right makes all the difference between a sparse harvest and decades of abundant spears.

Let’s get straight to the point. Asparagus is a heavy feeder, but it doesn’t want food all the time. Fertilizing at the wrong moment can even harm your plants. This guide will walk you through the simple annual schedule that guarantees strong, vigorous growth.

This heading is your core calendar. There are three key times in the year to think about feeding your asparagus bed. Missing one can set your plants back.

The Early Spring Feeding (At Spear Emergence)

This is your first and most visible feeding time. As soon as you see the first tiny spears poking through the soil in spring, it’s time to act. This feeding fuels the entire harvest season.

Why then? The plant is coming out of dormancy and using stored energy to push up spears. A nutrient boost now supports strong spear development and the coming fern growth.
What to use: A balanced, all-purpose fertilizer (like a 10-10-10) or a fertilizer slightly higher in nitrogen (like a 16-8-8) works well. Organic gardeners can use a generous layer of well-rotted compost or a balanced organic blend.
Key Tip: Apply this fertilizer before you start cutting spears, or right at the very beginning of the harvest period.

The Post-Harvest Feeding (Critical for Next Year)

This is the most important feeding for long-term health. After you stop cutting spears—usually in early to mid-summer—the plants needs to recharge.

Why then? Harvesting drains the plant’s energy reserves. This feeding fuels the growth of the tall, feathery ferns, which are the engine of the plant. The ferns photosynthesize and send energy down to the roots for next year’s crop.
When exactly? Apply fertilizer right after your last harvest, as the ferns begin to grow vigorously. Do not wait untill late summer.
What to use: A nitrogen-rich fertilizer is ideal here (like a 21-0-0 or a high-nitrogen organic option like blood meal). You can also use another application of compost. This promotes lush, healthy fern growth.

The Late Fall or Early Spring Clean-Up Feed (Optional but Beneficial)

This is a maintenance feeding. In late fall, after the ferns have turned completely brown and yellow, or in very early spring before any spears appear, you can add a gentle nutrient layer.

Why then? It slowly enriches the soil over the winter or provides a slow-release base for spring. It’s especially good for sandy soils that leach nutrients.
What to use: A top-dressing of finished compost or well-aged manure is perfect. Avoid strong chemical fertilizers at this time, expecially in fall.

What Happens If You Fertilize at the Wrong Time?

Getting the timing wrong can cause problems. Here’s what to avoid:

Fertilizing in Mid-Summer (Outside of Post-Harvest): This can stimulate tender new growth just before fall, which may not harden off before frost, making the plant vulnerable.
Fertilizing During Active Harvest: Applying strong fertilizer while you’re still cutting can sometimes lead to overly rapid, weak spear growth and may even affect flavor.
Over-Fertilizing: More is not better. Excess nitrogen, in particular, can lead to lots of fern but fewer spears, and can harm the soil ecosystem.

Choosing the Right Fertilizer for Asparagus

You have several good options. The best choice often depends on your gardening philosophy.

Balanced Synthetic Fertilizers

These provide nutrients in a readily available form. Look for a granular formula labeled 10-10-10 or something similar. Apply according to package directions, usually about 1 to 2 pounds per 100 square feet of bed.

Organic and Natural Options

These feed the soil as well as the plant. They release nutrients slower, which is ideal for a perennial crop.

Compost: The king of organic amendments. Apply a 1-2 inch layer as a top-dressing at any feeding time.
Aged Manure: Ensure it is well-rotted (at least a year old). Fresh manure can burn plants and introduce pathogens.
Fish Emulsion or Seaweed Extract: Great for a quick post-harvest nitrogen boost when diluted and watered in.
Balanced Organic Blends: Look for OMRI-listed fertilizers with a balanced N-P-K ratio.

Step-by-Step: How to Apply Fertilizer

Weed First: Always remove weeds from the asparagus bed before fertilizing. You don’t want to feed your competitors.
Water the Soil: If the soil is very dry, give it a good watering a day before. This prevents root shock.
Apply Granular Fertilizer: Sprinkle granules evenly over the soil surface, keeping them away from direct contact with spears or ferns. Focus on the root zone (about a foot out from the crown).
Incorporate Gently: For spring feeds, lightly scratch the fertilizer into the top inch of soil with a hand fork. For post-harvest feeds, you can leave it on the surface if you’re about to water.
Water Deeply: This is crucial. Water the bed thoroughly after application to help move the nutrients down to the root zone.
Add Mulch: After feeding and watering, renew your mulch layer (straw, shredded leaves) to conserve moisture and suppress weeds.

Special Considerations for Young vs. Established Beds

Your asparagus bed’s age changes it’s needs slightly.

Newly Planted Crowns (Year 1 & 2)

Do not harvest spears! The goal is to build the plant. Fertilize lightly at planting with compost mixed into the trench. Then, follow the post-harvest feeding schedule (even though you’re not harvesting) to support fern growth. Use milder, organic fertilizers to avoid burning tender roots.

Established Beds (Year 3 and Beyond)

These are the beds you harvest from. Follow the full three-step calendar outlined above religiously. Established beds are hungry and will show their appreciation for proper feeding with bigger, more numerous spears.

Signs Your Asparagus Needs Fertilizer

Watch your plants. They will tell you if they’re hungry.

Thin, Spindly Spears: Spears that are pencil-thin or fewer in number than usual often indicate a nitrogen deficiency.
Yellowing or Pale Ferns: Ferns that are not a deep, vibrant green may lack nitrogen or other key nutrients.
Stunted Overall Growth: If the whole plant seems smaller or less vigorous than in previous years, it likely needs a soil boost.

FAQ: Your Asparagus Fertilizer Questions Answered

Can I use tomato fertilizer on asparagus?

You can, but it’s not ideal. Tomato fertilizers are often higher in phosphorus (the middle number) to promote fruiting. Asparagus benefits more from consistent nitrogen for fern and spear growth. A balanced fertilizer is a safer bet.

Is Epsom salt good for asparagus?

Only if a soil test shows a magnesium deficiency. Epsom salt is magnesium sulfate. Adding it unnecessarily won’t help and can disrupt soil balance. Always test your soil first before adding specific amendments.

How often should you fertilize asparagus?

Stick to the core schedule: once at spear emergence, and once immediately after harvest. An optional third light feeding in late fall or very early spring is fine. That’s 2-3 times per year total.

What is the best natural fertilizer for asparagus?

Well-rotted compost is the best all-around natural choice. It provides a broad spectrum of nutrients, improves soil structure, and supports beneficial microbes. Aged chicken manure is another excellent nitrogen-rich option.

Should you fertilize asparagus in the fall?

A light top-dressing of compost in late fall after ferns die back is beneficial. Avoid using strong, high-nitrogen fertilizers in the fall, as they can stimulate tender new growth that winter frost will damage.

By following this simple calendar for when to fertilize asparagus, you invest directly in the future of your bed. Consistent, timely feeding builds resilient plants that will reward you with a reliable harvest for twenty years or more. Pay attention to your plants, feed them when they need it most, and you’ll enjoy the benefits of homegrown asparagus each spring.