How to Grow Asparagus: A Complete Perennial Growing Guide

Asparagus is a perennial (hardy up to growing zone 3) that needs plenty of time to establish a root system so it can survive the winter. If you are growing asparagus from seed, it is important to properly time your seed starting. 

The information on the back of the seed packet should tell you how many weeks in advance to start those seeds. I start asparagus from seed in February or March. (Here’s a full list of what I plant in February and what I plant in March.) Harden off your seedlings and plant them outdoors after the last frost.

If you bought bare root asparagus plants, get them planted as soon as possible! Don’t wait and don’t worry if there is still frost; they are very cold-hardy and intended to be put in the ground as soon as the soil can be worked. If you don’t plant them right away, you risk them breaking dormancy in the bag, which wouldn't be good. 

Before planting, submerge your bare root plants in warm water (about 65°F) for about 2 hours to hydrate the roots. That moisture will be crucial to helping the plant break dormancy. It is imperative that you plant it within hours of soaking it! You do not want to let the roots dry out again.

Pro-Tip: Do not plant dormant plants in soil that’s warm because you don’t want the plants to break dormancy too quickly. You want to kind of wake them up slowly.

Amending Soil for Asparagus

Prepping the soil for planting is especially important for asparagus! It’s a perennial that will come back year after year, so you can’t go back in two or three years from now and re-prep the soil. Make sure it's done right the first time so your plants will be set for the rest of their long lives.

Now, that’s not to say that you can’t add fertilizer later or amend the soil from year to year with a top-dressing of compost. You absolutely should do those! But the quality of the soil you plant in and the location that you choose should be great from the start.

With that being said, asparagus loves well-draining loamy soil high in organic matter. Asparagus have large, extremely vigorous roots. They don’t like to have wet feet or they will suffer from root rot or crown rot, or both.

To prepare the perfect soil, till the soil a foot deep. Prepare a 50/50 mix of sand and finished compost. Use that to amend the soil before planting. 

How to Plant Asparagus

The crowns of asparagus plants are very easily damaged. Be careful with them and always mark where you plant them. If you step directly on the planted crown or accidentally hit it with a garden tool, you can break the crown. If you damage the crown, the plant will die.

Growing asparagus in pots is not recommended. This doesn't allow for proper insulation during cold, harsh winters. Instead, follow these steps to properly plant out your asparagus:

1. Location - Choose a permanent location that is well-draining and receives at least 6 to 8 hours of direct sunlight each day. 

2. Prepare the Soil - In order to properly establish a deep root system, till the soil a foot deep. Amend the soil with a 50/50 mix of sand and finished compost until you have a well-draining loamy soil high in organic matter. The pH should be neutral, between 6.5 and 7.5.

3. Dig a Hole - Dig a big hole that is 8 to 10 inches deep (or a trench that is 8 to 10 inches deep when planting multiple plants).

4. Planting Depth - Whether you started asparagus from seed or bought bare root plants, the crown of the asparagus about two inches below the soil level when planted. With bare root plants, splay the roots out in the hole in every direction before back-filling with soil. Pro-Tip: Asparagus is one of the first plants to break dormancy; you most likely will still be getting frost at night when they start pushing up in the soil. If the crown is planted too shallow, it will break from the soil too early and get killed off by a frost.

5. Plant Spacing - Space your asparagus plants out about 1 to 1 ½ feet apart.

6. Water - Water your asparagus plants after planting. It's a common misconception that you don’t need to water asparagus after you plant them because it's spring and they are dormant, but the truth is that it is very important to water them in! The roots will start to take up water and work on growing root fibers and getting established before they even break dormancy. Watering also helps settle the soil around the newly planted roots, preventing air gaps.

7. Fertilize the Soil - I recommend ¼ cup of Trifecta+ per plant in the spring and fall every year. If you planted seedlings, fertilize the soil now. If you planted bare root plants, follow up in about a month when the plants break dormancy and fertilize with a good all-purpose fertilizer like Trifecta+. 

8. Mulch - Plants should be mulched to ensure good soil moisture during summer heat. If you are planting in a very sunny spot, make sure they are mulched year-round to protect the soil from drying out between waterings.

It takes 2 to 3 years for asparagus to fully mature. Do not harvest the spears in the first year!

How to Grow Asparagus: Fertilizing

Asparagus prefers a nitrogen-rich soil but also requires adequate phosphorus. Asparagus spears are actually the young shoots of the asparagus fern. These require nitrogen to promote green growth. 

Because asparagus is perennial, it has an aggressive root system that spreads quickly through the soil to become established before winter. Phosphorus is necessary for good root development. 

Fertilizing perennial plants is very important. I recommend using ¼ cup per plant of a good all-purpose fertilizer like Trifecta+ 2 times per year, once in spring to pull the plant out of dormancy, and once in the fall before the plant goes dormant to establish the roots before winter. 

Harvesting Asparagus

You don’t want to start harvesting from your asparagus in their first or second year! The plant is still getting established, and there is a high probability of killing the plant if you harvest the asparagus shoots too early. If you started them from seed, wait until the third year.

Pro-Tip: Bare root asparagus from MIgardener are two-year-old plants. You should not harvest them the first year after planting, but you may be able to harvest them the second year after planting.

When the asparagus shoots are bigger than the diameter of a pencil, you can go ahead and harvest them. If they are thinner than that, wait. Patience is key when it comes to asparagus. It’s always better to err on the side of caution. 

To harvest, snap off 8 to 10-inch-long spears that are less than 1 inch in diameter at the soil line before the buds open (or use a sharp knife to cut them off at the soil line). Leave spears smaller than a pencil to grow. 

Harvesting season starts in May and continues through June in most regions. Do not cut the ferns that grow after harvesting until they are completely dead in the fall or just before growth begins in the spring to avoid damaging the crown.