6 Things You Need to Know About Planting Asparagus

Thinking about growing asparagus? Get the dirt on raising these tasty springtime spears.

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Some people look to robins and tulips for their signs of spring. Me, I look for roadside signs that say “Fresh Asparagus.”

asparagus' 1st pick of the season

asparagus' 1st pick of the season

asparagus' 1st pick of the season

Where I live, people put coolers by the side of the road filled with bundles of homegrown asparagus. A plastic container full of money stands guard over the fresh produce. I like living where the honor system prevails, and I like it even more that it’s a place where people have an abundance of asparagus.

Asparagus crowns

Asparagus Crowns in Trench

Lay asparagus crowns in the trench.

I just broke ground on my own asparagus patch. I snapped the photo above at planting time (last weekend in Zone 6b). It looks like an invasion of land squids, but those are asparagus crowns. They’re the start of years of yummy springtime suppers.

Bed for Planting Asparagus

Asparagus Planting Bed

If space permits, give asparagus their own planting bed. Otherwise site them on the west or north side of the garden.

Photo by: Julie Martens Forney

Julie Martens Forney

Plan Ahead

Great asparagus crops don’t just happen—they’re the result of planning. First of all, you need to choose the right spot. Asparagus is a perennial, so you want to plant it where it can stay put. This vegetable sinks roots up to 10 feet deep and produces delicious stems from 15 to 30 years. This is nothing like a tomato or a pepper plant.

Asparagus yields best when it doesn’t have root competition, so any existing turf or weeds need to go. Asparagus really thrives in its own bed, which is what I did. That small bed in the foreground (above) is my asparagus patch. A narrow bed makes tending and harvesting easier.

Perhaps most important, asparagus is picky about soil pH—it needs alkaline soil (pH 7.2 or higher). Do a soil test and then add materials to shift the pH as necessary. (The soil test tells you what to add.) Soil tests aren’t difficult—look for a do-it-yourself kit at a hardware store or garden center. Expect to spend 99 cents for a one-use soil test or somewhere around $8 for a 10-test kit.

This intensive planning process, coupled with limited space, kept me from planting asparagus for years. The secret to success is this: Start your asparagus bed in fall, then plant in spring, which is when you find crowns for sale (more on crowns below).

Trench for Planting Asparagus Crowns

Measure Trench Depth

When planting asparagus, dig trenches 8 to 10 inches deep.

Photo by: Julie Martens Forney

Julie Martens Forney

Check Soil Temperature

I tried to grow asparagus once—but skipped all the planning process. That was Mistake No. 1. Guess how my asparagus patch fared? It didn’t. I had bare dirt. A wet spring and too-early planting yielded rotted asparagus crowns. Which brings me to Mistake No. 2: planting too soon. When you plant asparagus, soil temperature needs to be at least 50° F. Measure soil temps with a soil thermometer (if you have one), or follow soil temperatures online.

Various groups track soil temps, including some agricultural companies, the extension service (often pest divisions) and the U.S. Geological Survey. My advice is to search online using this phrase: “[your state name] soil temperatures.” You should be able to find a state map that allows you to drill down to your county. When you discover a result you like, bookmark it so you can find it again the next time you need it.

Purple Asparagus

'Purple Passion' Asparagus

'Purple Passion' asparagus adds color to salads and offers a sweet, tender bite.

Photo by: Gardener’s Supply Company at Gardeners.com

Gardener’s Supply Company at Gardeners.com

Soil temps are typically reported at 2-inch depths, and asparagus roots need to go in 8 to 10 inches deep. If 2-inch temps are in the mid-50s, deeper temps are probably good. You will never go wrong planting too late.

Research Varieties

Jersey Knight Asparagus Crowns

Asparagus Crowns

One-year-old asparagus crowns are fat and plump when they’re from a specialty nursery.

Photo by: Julie Martens Forney

Julie Martens Forney

Old-fashioned asparagus varieties include male and female plants. The females produce berries, which takes energy from the roots and effectively reduce future harvests. Newer introductions tend to be all male. Many came out of Rutgers University's research programs, so you’ll see names like ‘Jersey Supreme’ or ‘Jersey Knight’'. ‘Purple Passion’ (shown) produces purple stems (they turn green when cooked), and ‘Millenium’ blends strong winter hardiness with good yields.

Buy the Best Roots

It’s possible to grow asparagus from seed, but most home gardeners plant asparagus crowns. By starting with crowns, you’ll be picking the second year after planting. When buying crowns, look for a nursery that caters to commercial farmers and home gardeners. Place your order well before spring to reserve crowns before they sell out.

After much research, I bought my asparagus from Nourse Farms in Massachusetts. The crowns I received are 12 to 18 months old and huge—most are larger than my size 8 foot. Roots are fat and plump. Compare that to what you find at a discount store—small crowns with (often) dried up roots.

Asparagus Bed

Asparagus Trenches

Planting asparagus is time-consuming and a work-out because you need to dig deep trenches.

Photo by: Julie Martens Forney

Julie Martens Forney

With the supplier I chose, I was able to postpone the weekly shipment until soil temps were right. When I placed the initial order, I had to guess-timate a ship date. Then I adjusted it based on spring weather. This grower took all this in stride—it’s part of how they do business. Some companies sell older crowns at a premium price. The thing with planting older (and larger) crowns is that you risk greater transplant shock. Most extension agents don’t recommend it.

Get Ready for a Work-Out

Planting asparagus is hard work that includes digging 8- to10-inch-deep trenches. Using a raised bed can eliminate some of the digging. If you’re not up for that kind of heavy soil work, enlist the aid of an able body who will dig in exchange for fresh asparagus in years to come.

A 2-foot-wide bed—raised or in the ground—is a great option for planting asparagus. It’s just the right width to provide easy access. My bed is 5 feet wide by 10 feet long. I planted two rows with an 18-inch-wide buffer strip on the long side and a 12-inch buffer on the short side. The buffer strips provide a weed- and grass-free zone so the asparagus patch is easier to keep weed-free. I’m mulching the buffer strips with straw to help keep soil moisture in and weeds out.

Detect Any Odors?

This last item isn’t something you need to know before planting, but it’s definitely worth knowing. This tidbit becomes more relevant once you start eating your asparagus harvest. Asparagus produces a strong scent in urine as soon as 10 minutes after eating—and the scent is even more pungent when you eat freshly picked spears. Maybe you have detected it.

Researchers have studied this urine anomaly, and what they know is this: Everyone produces the chemical changes responsible for the odor, but not everyone has the genetic code that enables them to smell it. How’s that for some asparagus trivia?

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