Asparagus Growing Secrets: How to Harvest Big Spears at Home

Asparagus is one of the first harvestable vegetable crops each spring. It also happens to be one of only a handful of perennial vegetables, returning to the garden each year, with yields bigger and better than the season before. While asparagus plants are productive for many, many years, it can be somewhat of a challenge to get them established. For the best asparagus harvest possible, you’ll need to understand the stages of asparagus growth and follow a few simple guidelines for variety selection, planting, harvesting and maintenance. In this article, I’ll share some of my best asparagus growing secrets from my time as an organic market farmer.

Where to plant asparagus — Asparagus is an investment. The plants produce for years, but they take a good bit of time to get established.

How does asparagus grow?

It’s important that asparagus plants (Asparagus officinalis) are planted and cared for in a particular way for the first few years of their life so they can build up enough energy to begin to produce thick, delicious, edible spears. Asparagus grows from underground crowns with plump white roots. Only the crown and root system survive the winter; everything above the ground does not. The plants are winter hardy (down to about -40°F), and they perform well in all but the warmest growing zones. Asparagus plants require a winter dormancy. Throughout a single growing season, asparagus plants pass through three distinct stages.

Perennial vegetables for the garden — Whether you grow purple asparagus varieties or green, the plants have three distinct growing stages.

Stages of growing asparagus

There are three main stages of asparagus growing. The first is the spear stage. The second is the fern stage. And the third is the dormant stage which happens in the winter. Let’s talk about each of these stages and how it affects the health and productivity of your asparagus patch.

The spear stage of growing asparagus

The spears of asparagus plants are produced in the first stage of growth. Asparagus spears are actually the young, undeveloped stems/shoots. This is the edible stage.

For mature plants, the spear stage lasts between 6 and 8 weeks, beginning in late April or early May, depending on which gardening zone you live in. Spears typically begin to emerge when the soil temperature reaches 50°F. The asparagus growing in my Zone 5 Pennsylvania garden begins to appear around the same time the blueberry bushes develop their blooms. The spears are fast-growing, extending between one or two inches in length each day. This is the timeframe in which asparagus should be harvested. Do not harvest spears from your plants for longer than this 6-8 week period or you’ll be affecting the future productivity of your plants (more on how this happens in the next section).

How to cultivate asparagus plants — You’ll see new spears emerging from the crown of the plant soon after soil temperatures reach 50°F.

The fern stage of growing asparagus

When left to mature, the spears grow into tall “ferns” covered with many tiny leaves. Though asparagus in the fern stage isn’t edible, it is a very critical period for the plants. The ferns that develop in your asparagus patch as the plants mature are photosynthesizing and building up food stores to send down to the root to fuel next year’s spear production.

This fern production is critical to the success of your asparagus patch long term. The number of spears produced in each season, and the overall vigor of the plants, is affected by how many ferns are left to mature and how healthy they are. The bigger the ferns, the more food is created to fuel the following year’s spear production. Asparagus ferns can grow up to 6 feet tall! Do not cut the ferns down until late winter, after they have been completely killed by frost. Alternatively, you can wait until the early spring to cut them down. Please visit our article on when to cut back asparagus and why fall may be a better choice for more info on the subject

Asparagus growing secrets for the garden — When asparagus plants are in the fern stage, they aren’t edible, but it’s an important phase because it supports future spear production.

The dormant stage of growing asparagus

Though the plants are not actively growing above ground during the dormant stage of growth, there is a lot going on beneath the surface of the soil. The food that was produced by the ferns during the growing season, travels back down into the crown and the roots of the plant in the autumn, as the fern dies back. Those carbohydrates are held in the dormant crowns through the winter. This dormancy period is critical, and it is why asparagus grows best in regions that receive cold winter temperatures (USDA Zones 3 to 8). Until the ground freezes solid, the crowns and roots of your asparagus plants will continue to grow. Mature asparagus crowns can reach up to 5 feet in diameter, and the roots can grow several feet deep. As they grow, they are developing more buds that can produce more spears in subsequent seasons.

Now that you know the three stages of growing asparagus, I’d like to share a few asparagus growing secrets to put you on the road to success.

Asparagus varieties for the home garden — There are many varieties of asparagus, but all male types tend to produce the biggest spears because they don’t put energy into creating seeds.

The best asparagus varieties for big spears

Ideally, when planting asparagus, you should select a cultivar that consists of all male plants. Like holly plants, asparagus plants are monoecious, meaning that each plant is either male or female. All-male asparagus varieties, like hybrids ‘Jersey Knight’ or ‘Jersey Supreme’, are propagated by division to keep the variety all male. These selections tend to reach maturity faster and produce larger spears than female asparagus varieties due to their lack of seed production which can sap a lot of energy from the plant. Yes, varieties with a mix of male and female plants sometimes drop viable seeds that go on to grow new plants, but it can take many years for these seedlings to become mature enough to harvest. The benefits of planting crowns of “all male” varieties far outweigh an occasional seedling popping up.

Early spring crops for the vegetable garden — Female asparagus plants produce small red berries with seeds inside. The seeds can produce more plants, but that can lead to a crowded asparagus patch and take many years.

Where to site your asparagus plants

Select a site where your asparagus can live for many years. Remember, asparagus plants produce for 20 years or more. The asparagus bed should also receive a minimum of eight hours of full sun per day and be well-drained. Too much shade means small spears and weak production. Before planting, test the soil’s pH and adjust it if necessary. The target soil pH for asparagus is 6.5 – 7.0. Asparagus does not perform well at a pH much below 6.0. A soil test will accurately assess your pH and make recommendations based on the results. My native soil has an acidic pH around 5.5, so every few years I have to add crushed limestone to my asparagus patch to raise the pH. My soil test results tell me how much to add. I test my vegetable garden’s pH every 3 to 4 years.

Asparagus growing: Where to plant and how to harvest — Asparagus plants need 8 hours of full sun per day. This allows the ferns to create plenty of food to fuel the next season’s spear production.

How to plant asparagus crowns for the best harvests

One-year-old crowns are usually purchased in bundles of 10 to 25 bare-root plants. Because they are kept out of soil and in storage for many weeks before they’re shipped out to garden centers for sale, it’s important to handle the crowns correctly before planting. I’ve had the most success soaking the crowns in tepid water for one or two hours before planting.

What do asparagus crowns look like? — Asparagus crowns have thick roots emerging from them. Soak the crowns in water for a few hours prior to planting.

Before you plant, work a good amount of organic matter, such as well-aged horse manure, compost, or leaf mold, into the planting area. Then dig a long, 10-inch-deep trench. Place one crown every twelve inches down the length of the trench, spreading the roots out and making sure the central growing tip is pointed up. Cover the crowns with a few inches of the amended backfill. The best planting time is in the early spring, about 6 weeks before it’s time to plant your tomatoes.

A few weeks after planting, when the first tiny spears begin to grow, backfill with a few more inches of soil, piling it right up on them. Repeat the process every few weeks until the trench is completely refilled. The deeper the crowns are (up to a depth of 10 inches), the more resilient the plants will be.

How to plant asparagus — Dig a deep trench and place the crowns down the trench. Do not cram the roots into the planting hole; spread them out.

When to harvest asparagus for bigger spears

Asparagus is a crop that requires patience. But for patient gardeners, the rewards are nothing short of amazing. Do not harvest any spears until the plants are at least three years old (see what I mean about patience?). During the first year and the second year, allow all the spears to go to fern. In the third year, any spears thicker than a pencil can be harvested. Stalks thinner than a pencil should be allowed to mature into ferns to feed the roots for the following year.

When the plants are three years old, the harvest period should last only four weeks, but once the plants reach four years of age, harvests can occur over the 6-8 week period known as the spear stage. That time frame starts with the emergence of the first spear of the season. Cut mature spears every day at ground level with a sharp knife when they are between 4 and 10 inches tall. Try to harvest them before the ferns begin to expand from the spear.

If you miss a few spears because they grew so fast, don’t worry about it. Just let them develop into ferns. Doing so will not hurt the plant; instead, it will go on to photosynthesize and produce more food for the growing crown.

After spear harvesting ceases for the season, allow all of the spears to develop into the ferns and generate fuel for next year’s production.

Vegetable gardening in the spring — It takes several years for the spears to be large enough to harvest, but after that, you can look forward to decades of harvests.

Maintaining asparagus plants

To maintain your asparagus patch, keep it well weeded, especially during the first few years when the plants are small. Water your patch regularly throughout the first two seasons, until the plants become well-established. After that, there’s no need to water except in times of extreme drought. Remember, those crowns are deep and have an extensive root system, making the perfectly capable of accessing water and nutrients on their own.

It’s often recommended to add a layer of mulch your asparagus patch with 2 or 3 inches of shredded leaves or straw in the spring, before the spears emerge. This prevents weeds and helps maintain soil moisture levels. I do not mulch my asparagus plants, however, because I find that the mulch acts as a safe haven for asparagus beetles through the winter. (There’s more on managing asparagus beetles and other pests in this article.) Instead, I hand-weed around my asparagus plants. The choice is up to you.

How to mulch asparagus plants — If you don’t want to hand-weed, mulch your asparagus patch with straw, grass clippings, or shredded leaves.

Fertilizing asparagus plants

Top-dressing the asparagus patch with an inch of compost each season provides most of the nutrition the plants need. However, you can also fertilize asparagus with an organic granular fertilizer that contains an equal percentage of nitrogen, phosphorus, and potassium (5-5-5 for example) once per year, ideally in the early spring. Sprinkle it along the sides of the plants and lightly scratch it into the soil down to a depth of 1 inch.

Vegetable garden companion planting — Asparagus ferns look lovely in the summer garden combined with other vegetables, herbs, or flowering plants.

Once established, asparagus patches can produce wonderful crops of spears for twenty-plus years. They are an exercise in patience, but they are also well worth the wait.

For more on growing spring crops, please visit the following articles:

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