Introduction
A classic spring treat, asparagus is a perennial that will produce tender spears every spring for many years.
About Asparagus
Asparagus is grown from 1-year-old plants or "crowns," which are planted in early spring as soon as the soil can be worked. Asparagus plants take three growing seasons to reach full production, although light harvesting can begin in the second year. Once established, an asparagus planting will provide abundant harvests for fifteen to twenty-five years. Allow ten to twenty plants per person (15 to 30 feet of row).
Choosing Varieties
Asparagus varieties fall into two categories: all-male hybrids (more productive, fewer berries) and open-pollinated types with male and female plants. The following varieties are recommended based on climate and soil conditions:
All-Male Hybrids (Jersey Series):
- 'Jersey Knight': Vigorous, rust-resistant, adapted to clay soils and warmer climates
- 'Jersey Giant': Best for cold climates, produces spears 7 to 10 days earlier than Jersey Knight
- 'Jersey Supreme': Latest in the series, produces uniform spears, disease-resistant, best for sandy soils
Other Varieties:
- 'Purple Passion': Uniquely colored purple spears, widely adapted
- 'UC 157': California hybrid adapted to warm climates with mild winters
- 'Viking KB3': Open-pollinated variety, better producer than traditional 'Martha Washington'
Choosing a Site to Grow Asparagus
Select a well-drained site in at least part sun; full sun is not necessary. Asparagus will thrive in slightly acid soil (pH of about 6.5), but will tolerate alkaline conditions up to 9.0.
Planting Instructions for Asparagus
Eliminate all weeds by repeated tilling. Loosen the soil to a depth of 12 to 15 inches, then mix in a 2- to 4-inch layer of compost. Prepare the bed by digging trenches 4 feet apart. The trenches should be 12 inches wide and 6 to 12 inches deep. Soak the crowns briefly in lukewarm water before planting. Draw a hoe along each side of the prepared trench to form a mound in the center running the length of the trench. Set the crowns 18 inches apart on the mounds in the trench, draping the roots over the sides. Cover the crowns with a mix of one part compost to three parts topsoil, burying the crowns 2 inches deep. Water the bed thoroughly. After about a month, once shoots have appeared, carefully add more soil to the trench.
Ongoing Care of Asparagus
First year: Weed the beds frequently, taking care not to disturb roots. Periodically add more topsoil/compost around the emerging shoots until the trench is filled. Then spread a 4- to 8-inch layer of mulch, such as hay or leaves, around the base of the plants. Water regularly. Do not harvest any spears the first year. Cut down dead foliage in late fall and side-dress with compost.
Second year: Cultivate lightly by hand until the new spears are several inches tall. Keep the bed thickly mulched. Side-dress with compost in the spring and early fall. Cut down dead ferns in late fall. You may harvest very lightly the second year.
Third year and beyond: Maintain as for the second year, and begin harvesting.
Frost Protection
Emerging asparagus spears are frost-tender, with damage occurring around 28 degrees F. If frost is predicted during early spring harvest, cover the bed with black plastic to protect emerging spears. Research shows this protection reduces frost damage from approximately 80 percent down to 17 percent.
Season Extension
For a longer harvest, try the mother stalk technique: instead of harvesting all spears in spring, allow the first three large spears per crown to grow into ferns. These developing ferns feed the crown, allowing continued production weeks longer than normal harvesting. You can harvest surrounding smaller spears while the mother stalks develop, potentially extending harvest from the normal 6 to 8 weeks into summer. This technique works best with vigorous hybrid varieties like the Jersey series and requires consistent watering throughout the season. Stop harvesting once new spear diameter becomes thinner than a pencil.
How to Harvest Asparagus
Plants started from crowns can be harvested lightly in the spring of the second year. Begin harvesting in earnest the third year. Harvest only those spears that are thicker than a pencil. Cut off the spears at or just above ground level when they are 6 to 8 inches tall.
Growing White Asparagus
White asparagus is any asparagus variety grown in the dark through blanching. The spears are more tender and have a milder, nuttier flavor than green asparagus. To grow white asparagus, keep the emerging spears in complete darkness during harvest season using an opaque cover such as plywood or a box frame. Cover the bed for the entire harvest period, lifting the cover only during the few minutes needed to cut spears every couple of days. This blanching keeps spears white and tender. Most traditional asparagus varieties can be used; simply manage them under cover during the growing season while allowing full sun exposure in summer and fall for plant vigor.
Frequently Asked Questions about Asparagus
Which variety should I plant, and does all-male really matter?
It matters more than which named cultivar you pick. Nearly all asparagus breeding for the last two decades has gone into all-male hybrids, for three reasons: yield, reduced pest pressure, and safety.
Female asparagus plants produce bright red berries in late summer, after spear harvest ends, and those berries are toxic. They contain sapogenins and related compounds that cause gastrointestinal upset in people and more serious effects at higher doses. In a household with children or pets this is a genuine hazard, because the berries cluster at eye level in a garden bed where a child or an animal investigating the garden can easily reach and mouth them. All-male hybrids do not set berries at all, which removes the problem rather than managing it.
Beyond safety, female plants divert real energy into berries and seed instead of spears, and the seed they drop produces volunteer seedlings that are themselves female and perpetuate low-yield genetics.
On names: the Jersey series (Jersey Giant, Jersey Knight, Jersey Supreme) was the standard for decades, but commercial seed production for it ended more than ten years ago and crowns are no longer reliably available. Modern all-male hybrids in current production include Millennium (cold hardy and widely available), Empire (early season), Apollo (tender and good for freezing), and Atlantic. The differences among these are small; the difference between any all-male hybrid and a mixed male and female planting is large. Choose whichever your seed source lists, and if a catalog description does not say "all-male" or "hybrid," ask the seller before ordering.
For very cold regions wanting an exceptionally early type, Gaspe is a traditional open-pollinated landrace from Quebec, with a short harvest window and very early maturity. Note the tradeoff: it produces both male and female plants, so it bears the toxic red berries. If berries in the garden are a concern, stay with the all-male hybrids.
How deep should crowns go, and does the old deep-trenching advice still stand?
Plant crowns 6 to 8 inches deep. That is shallower than the 12 to 15 inch trenches mid-twentieth-century references called for, and the change is deliberate: deeper planting does not improve establishment, yield, or longevity. Asparagus roots develop throughout the soil profile rather than only at the planting depth, and the plant anchors itself perfectly well at 6 to 8 inches, while the shallower depth is easier to dig and easier to cut from later. If you meet an older reference recommending deep trenching, you can set it aside.
Two related points. Research has shown crowns do not have to go in right side up; planted upside down or sideways they right themselves as the shoots emerge. Setting them root side down with the buds facing up is simply a convenience. And do not press or pack the soil over them. Gentle coverage is enough, and the bed levels out over the season.
What if my crowns are already sprouted, or I cannot plant them this year?
Sprouted crowns can still be planted at the recommended depth without harm. The shoots will grow upward and poke through as the soil settles. Follow the standard planting instructions, and do not harvest from first year plants regardless of sprouting.
Storing crowns for a year is not an option. Crowns kept dry shrivel and crowns kept moist rot, and either way most of the stored energy is gone by spring. You have two realistic choices, and both involve soil.
Heel them in. Dig a shallow trench in a protected spot, such as under a shed, against a north facing building, or in a corner of the garden. Lay the crowns at an angle, cover them with soil, leaves, or mulch, and leave them until very early spring, watering if the winter is unusually dry. Then dig them out and move them to their permanent bed. Yes, you are moving them twice, and yes, they will still be alive.
Plant them now, even imperfectly. In a holding bed, in temporary rows, a bit too shallow or too close together, it does not matter much. They will survive and establish, and you can move them later or simply leave them. A hasty planting beats a crown killed by a year in a bag.
How should the bed be enriched before planting?
Asparagus stays in the same ground for fifteen years or more, so the one chance to improve the soil deeply is before the crowns go in. Dig in a generous quantity of well rotted manure or finished compost across the whole bed rather than only in the planting trench, since the roots will eventually spread far wider than the row. Aim to mix a substantial layer of organic matter into the top 8 to 12 inches, turning it in thoroughly rather than spreading it on top. It improves structure in both directions, making clay more workable and sand more retentive, and it creates the loose, friable texture the roots want.
A complete garden fertilizer worked in at the same time gets the planting off to a faster start; use one that supplies phosphorus and potassium along with nitrogen, and follow the application rate on the label. Bone meal is a traditional amendment supplying readily available phosphorus, which encourages deep root development in new crowns; work it in at planting according to the package directions. Have the soil tested if the bed has never been cropped. After planting, spread 2 to 3 inches of organic mulch around the crowns to suppress weeds and slow evaporation, both of which matter in the first season.
What pH does asparagus want, and how do I get there?
Aim for 6.5 to 7.0. Asparagus is one of the few garden vegetables that genuinely prefers soil at the top of the neutral range, and a reading in the high 5s is worth correcting before the bed goes in, since you can work amendments through the whole root zone then and never get another chance. Acidic soil below that range limits nutrient availability and favors certain soil pathogens. Well above 7.0 is less of a concern for this crop.
If you have just limed, stop and wait. Lime works slowly, and the temptation to add something on top of it is how beds end up overshot past 7.0, which brings its own nutrient problems and is far harder to undo than a low reading. Pelletized lime acts faster than the coarse granular product, so if that is what you used you will see movement sooner. Give it a couple of months, then run another soil test and decide from the number rather than from impatience. Where a test recommends lime, use agricultural lime at the rate your soil test results call for; your local extension office can help you read them.
If the test still reads low, wood ash will nudge it up, worked gently into the soil between the rows where you are not disturbing the crowns. Keep ash off the roots and off emerging spears, use it sparingly since it is far more reactive than lime, and wear gloves and eye protection, because wood ash is caustic when wet. Once you are at about 6.5, stop and leave the bed alone.
I planted crowns three weeks ago and nothing has come up. Do I dig them up?
Almost certainly not. New crowns are often very slow to show, and cold spring weather, deep planting, and heavy or wet soil each add to the wait. The crowns spend that time settling in and pushing roots before they send anything up, and once they do start, the spears come up startlingly fast.
If waiting is unbearable, dig carefully down to one crown at the edge of the planting and look at it. A firm crown with pale new root tips or a fat bud starting is doing exactly what it should. Cover it back up and leave the rest alone. A crown that is soft, dark, and foul smelling has rotted, which usually means the site holds water.
The one thing that matters in that first season is water. Asparagus wants soil that is rich and moist but drains freely, never soggy, and a first year planting needs steady moisture to build the root system that carries the bed for the next couple of decades.
How long do I have to wait before I can cut spears?
Longer than feels reasonable, and this is the single most important practice for a bed that produces for decades. Allow the spears from a newly planted bed to grow into full foliage rather than cutting them: the foliage manufactures the sugars the crown and roots need to expand, and every spear you cut is leaf area the plant does not get. Beds harvested too early often underperform for the rest of their lives.
A light harvest can begin once the bed is established, cutting for three to four weeks and then letting the rest grow into fern, and full harvest of six to eight weeks follows a year later. In every season, stop cutting when new spears come up thinner than a pencil; that is the plant telling you it has spent what it had. Harvest only spears thicker than a pencil, cut at or just above ground level when they are 6 to 8 inches tall, and stop by early summer so the fern has an uninterrupted run at feeding the crowns.
Why are my spears thin, and why are they ferning out so quickly?
Those are two separate things with different causes. Thin spears mean the crowns are young or depleted. Rapid ferning, the spears opening into feathery foliage, is purely a temperature response.
A young crown, or one weakened by aggressive harvesting the year before, sends up thin spears, and that is normal. As the crown ages and stores more energy underground, the spears thicken. An established bed of three years or more produces spears about pencil thick or better if the crowns are healthy. If yours are thin, stop cutting when they drop below pencil thickness, which lets a young or recovering crown build energy instead of losing more.
Warm spring weather makes spears open faster into fern. A cold spring keeps them closed longer, which is why the same spear thickness stays harvestable for longer in a cool year.
My bed's harvest dropped this year. Did cutting the ferns in spring cause it?
No. Cutting ferns down in early spring before new spears emerge is standard practice and often preferred; leaving them standing over winter is also common, because they hold snow over the crowns. Neither is the cause of a yield drop.
The likelier culprits are these. You may have overharvested in a previous bumper year, cutting harder or later than young crowns could stand, since the crowns rebuild their energy during the fern season. Soil fertility and moisture may be dropping off, because asparagus draws heavily from the same ground for years. Weeds may be taking hold and competing for what the soil has left. Or the bed may simply be fluctuating, which established beds do, especially after a stress like drought, flood, or a late frost that you did not notice at the time.
The fix is the same in every case: run a soil test for fertility and pH, add compost or aged organic matter to the top of the bed, mulch to suppress weeds and hold moisture, water deeply during dry spells, and stop harvesting by early summer so the fern can do its work.
The ferns grew four feet tall and fell over
That is common and not necessarily a sign of anything wrong. Tall summer fern gets top heavy, and once it is fully leafed out it flops, especially after rain or wind.
Staking each plant is a waste of an afternoon. The easy method is to drive one stake at either end of a row and run a length of twine between them down both sides, so the ferns are held between two lines. One pass with two stakes and a ball of string does the whole row, and you can add a second string higher up as the ferns gain height. Keeping the fern upright matters because it needs to photosynthesize until frost, and a collapsed mat of fern on the soil holds moisture and encourages disease.
If you suspect the crowns went in too shallow, resist the urge to shovel more soil onto the bed. Adding soil over an established planting is awkward and tends to bury the crowns unevenly. Instead, every fall after you cut down and clear away the old stems, topdress heavily with well rotted manure or compost and add an organic mulch on top. That feeds the soil, insulates the crowns, suppresses weeds, and over several seasons quietly raises the level over the roots, which is the outcome you wanted.
A caution on the other side. Asparagus beds are easy to overfeed because they stay in one place for decades and get a compost dressing every year. Very heavy annual loads of compost and manure build up potassium, and there is a reasonable argument, made by people who work with the crop commercially, that excess potassium works against magnesium and manganese and gives you weak, thin stalks. The evidence here is not settled, but the practical advice is sound either way: a moderate annual dressing beats a huge one, and a soil test every few years is worth more than a rule of thumb.
Should I spread rock salt on the bed to kill the weeds?
This is an old practice with real history behind it. Asparagus tolerates salty soil better than most weeds do, which is why saline coastal ground grew wild asparagus and why gardeners a century ago salted their beds. Some old sources went as far as a pound per square foot, and separate advice existed for a much lighter dose of sodium chloride on the theory that it helped crowns resist fusarium crown and root rot.
We do not recommend it now. Salt does not break down or wash away cleanly; it moves into the subsoil and into whatever is downhill, it degrades soil structure so the ground packs and drains worse over time, and once you have salted a bed you have committed that patch of ground for a long time, including for whatever you might want to grow there after the asparagus is done. The fusarium argument has also been overtaken by better varieties, since the modern hybrids are bred for resistance to exactly those diseases.
What actually keeps a bed clean:
Start clean. Weeds are far easier to beat before the crowns go in. Give the site a full season of clearing if you can, particularly for perennial weeds with running roots, because bindweed or quackgrass through an asparagus bed is close to unfixable once the crowns are planted.
Mulch heavily and every year. A thick layer of compost, or newspaper or cardboard covered with straw, does most of the weeding for you and improves the soil while it does it. This is the single most effective thing on the list.
Weed by hand, shallowly, and often. Asparagus roots run wide and near the surface, so a hoe does damage. Pull what comes through the mulch while it is small. A mature stand shades out many weeds on its own after the first season.
Consider a labeled pre-emergent if the bed is large. Corn gluten meal is the one gardeners most often use, and some report it cuts hand weeding substantially over a season. Understand what it does: it interferes with seedling root development, so it prevents new weeds from establishing and does nothing at all to weeds already growing. It is also a significant source of nitrogen, which counts toward what you are feeding the bed. Apply any product, this one included, according to its current label for asparagus, and time it before weed seeds germinate rather than after.
Whatever you use, remember that this is a perennial food crop. Any herbicide near an established bed has to name asparagus on its current label, and the preharvest interval matters here more than in an annual garden, because the spears you cut come up through exactly the soil you treated.
How do I keep deer out of the asparagus?
Deer treat an asparagus bed as a delicacy, and the way they browse makes it worse than the volume they eat. A deer takes a bite from one spear, moves to the next, takes a bite from that, and works down the row, so a short visit ruins far more spears than it consumes.
A four foot picket fence will not stop them. To exclude deer with a fence you are looking at eight to ten feet of height, which is a serious piece of construction for a vegetable garden.
Cheaper things that work:
Cage the bed rather than the garden. A hoop of chicken wire bent over the whole asparagus bed keeps noses off the spears, and it does not have to be neat or permanent. For the few weeks of cutting season this is the most reliable answer available for the money.
String line around the perimeter. Run fishing line, or any thin line they cannot easily see, from tree to tree or post to post around the boundary, and vary the height as you go, roughly between two and four feet off the ground. A deer that walks into a line it did not see startles and turns back. It is not a barrier so much as a bad experience, and it will not hold up against a determined herd, but it is inexpensive and many gardeners get years out of it.
Do not put food out. Feeding deer at the edge of a garden does not buy you peace, it buys you resident deer. Once they have finished what you offered they carry straight on into the garden for the next course. Supplemental feeding is also illegal in a number of states because of disease spread in deer herds, so check local rules before considering it at all.
One caution on line and wire: string them where people are not going to walk into them, and flag them with tape or cloth at head height so nobody catches a line across the face in the dark.
What about asparagus beetles and rust, and does planting onions nearby help?
The asparagus beetle and asparagus rust are the two pests worth knowing. The beetle feeds on both spears and foliage; rust is a fungal disease that weakens plants and cuts the following year's production. A newly planted bed is generally not threatened by either straight away, but both turn up as a bed matures.
Companion planting with onions or other aromatics is sometimes suggested, on the theory that strong smelling plants mask the asparagus or act as a trap crop. The theory is plausible and the evidence for it is limited. It may offer a modest benefit, it is not necessary for success, and it is entirely optional. Nothing about it substitutes for good siting, good drainage, and clean fall cleanup.
For active pest or disease management, ask your local extension office what is currently recommended in your area. If you use any pesticide or fungicide on asparagus, the product must carry an asparagus label, and you must follow its rates, timing, application method, and preharvest interval. This is a food crop you will be cutting from for decades, and products used on the bed can leave residue on spears you harvest later.
Can I replace dead or weak crowns without damaging the good ones around them?
Yes, with careful technique and realistic expectations.
An established bed has huge root systems running outward from each crown and down several feet, so digging out a weak plant inevitably cuts through its neighbors' roots. Established crowns tolerate that, but it is a shock worth minimizing. Dig with a narrow spade or fork, go straight down rather than prying outward, remove the weak crown, break up the soil in the hole, and set the new crown with its eye about 2 to 3 inches below the surface. That is shallower than you would plant a new bed, and it keeps the disturbance to the neighbors down. Fill in without compacting, and water well.
The realistic timeline: a new crown planted into an established bed spends two or three years playing catch up, shaded by the ferns around it and producing thin spears or none. The established plants lag slightly from the root disturbance and recover within a season or two. After three or four years you may get a reasonable harvest from the newcomer, and the older plants will still dominate.
If more than about 10 percent of the bed is weak, consider starting a new bed in fresh soil instead. A whole new bed comes into production faster than patching many weak spots, and you end up with one bed still producing while the other establishes. Beds can last twenty years or more, but they do decline eventually, often after fifteen to twenty years as crowns age and soilborne pathogens accumulate, so a succession plan is good practice. Starting fresh is also the moment to move to modern all-male genetics if your old bed does not have them.
Are there safety points I should know about handling asparagus?
Three, and none of them are in most growing guides.
The red berries on female plants are toxic if eaten. They appear in late summer, they sit at a child's eye level, and the risk is in eating them rather than in handling them. In a household with children or pets, plant all-male hybrids and clear any berries that do appear.
Some people get contact dermatitis from the cut plant, meaning itching, redness, or a burning feeling on skin that touches cut spears or foliage, and it is worse when the plant is wet. It is usually mild and passes within minutes to hours, though it can be stronger in sensitive people. Wear gloves or long sleeves for harvest and trimming, wash your hands and any exposed skin afterward, and rinsing the spears under running water as you prepare them cuts down the contact.
Wood ash is caustic when wet, so glove up and protect your eyes if you use it to raise pH, and keep it off the crowns and spears.
