HOW TO GROW ASPARAGUS

If you’re an asparagus lover like me, you really should be growing your own crop. Nothing beats the taste of your own freshly harvested asparagus spears. So why don’t people rush in and grow asparagus? Probably because we are more into instant gratification vegetables with a quick turn-around time. And asparagus, which is slow to mature, certainly isn’t a quick bang for your buck type of vegetable.

Instead, you have to invest considerable time in it, but consider this: asparagus plants, properly cared for, can continue for 20 to 30 years. So, what if you have to wait two, or optimally three, seasons before you start harvesting your first crop. The sooner you plant, the sooner you’ll be enjoying this amazing vegetable.

What sets asparagus apart from most vegetables is that, like rhubarb, it is a perennial: it will come back year after year. In addition, it is unusual in that you harvest first, and then grow on the leaves in the form of fern fronds which fuel the crop production for the following season.    

WHAT ZONE WILL ASPARAGUS GROW IN?

Asparagus is considered hardy in the U.S. Department of Agriculture zones 3 to 10. Some varieties may be better suited to growing in extremely cold or very warm areas. When purchasing from an online supplier, consult their website for the best variety suited to your particular zone.      

LOCATION

Asparagus does not like root disturbance; avoid relocating your plants.  Once you plant them, you want to leave them be. So, careful consideration should be given as to where you plant them.

Asparagus likes full sun—8 hours’ worth—if possible. Lack of sufficient sunlight will result in thin spears and weak plants.

You can grow asparagus in conventional garden beds, or raised beds, or even large containers. Wherever you choose to grow asparagus, make sure that the area is committed to just asparagus. They don’t do well sharing their space!      

Asparagus growing in a raised bed

THE RIGHT SOIL

The soil mix should be rich and friable; incorporate as much humus and compost, peat, well-rotted manure (cow if you can get it), worm castings, etc. as you can.  The soil is going to be there for a long time, so the initial soil mix is part of your investment in this crop. Aim for providing optimum nutrients at the time of planting to provide for a healthy, long-lived stand of asparagus.

The soil should be well-drained—wet-feet will encourage disease and root rot. Asparagus being deep-rooted requires a good depth of soil: 18” to 24” is optimal. Asparagus thrives in a slightly acidic soil of 6.5 to 7.0.

MALE OR FEMALE PLANTS?

Asparagus is unusual in that it is ‘dioecious’. This means it is either male or female. (Many plants are both). While both sexes produce asparagus spears, male asparagus plants will produce a heavier crop of bigger spears.

Interestingly, both male and female asparagus plants produce flowers, but only the female plants will produce berries—which are toxic to humans. (Hence the reason why their spears are inferior to those of male plants, as the nutrients are directed into berry production and thus seeds.)    

Berries on a female asparagus plant

Growing just MALE asparagus plants is considered the optimum. However, even your own female asparagus spears will probably outshine store-bought asparagus.

If you want to remove female plants, you will need to leave the plant unharvested over winter and wait for the fern-like foliage to develop berries. If the ferns have no berries, then you have scored with a male plant. Remove volunteer seedlings arising from your plants as these will be inferior to male plants.

There is one other fool-proof way of ensuring that you only grow male plants and that is by selecting male-only varieties. I have noted these in the next section.

ASPARAGUS CROWNS

Asparagus is usually grown from roots known as crowns; essentially a cluster of dormant buds attached to a clump of roots. These crowns are the roots of 1 to 2-year-old asparagus plants.

The crowns are planted in early spring. These bare-roots arrive and should be planted as soon as possible so as not to dry out. When planting, follow the supplier’s instructions. Many bare root plants benefit from the roots being rehydrated by a gentle soaking in lukewarm water.

Crowns are available online from various suppliers. In the US I have had excellent results from Starke Bros who carry a number of varieties including the well-known Heirloom variety Mary Washington, Jersey Knight Giants (male) and Purple Passion. Not surprisingly, the latter variety is purple, but cooks up green!     

Asparagus comes in purple too!

Renee’s Garden is another good source for asparagus crowns and offers Millenium (male) and heat-tolerant Purple Passion.

Incidentally, if you are wondering where to purchase asparagus plants with white spears, that isn’t a ‘variety’. Rather it is regular asparagus that has been blanched white – in other words, light has been excluded during the growing process, just as is done with Belgian Endive.

You can grow asparagus from seed. It can be hard to germinate and it will lengthen the time till harvest still more. Plus, you will get male and female seedlings. So, you want to ask yourself if it is worth it? I would opt for crowns, if possible.

HOW MANY CROWNS DO I NEED?

You may well wonder how many plants to grow per person. A well-grown adult asparagus plant should produce ½ pound of asparagus spears each year. The rule of thumb is to plant 5 – 20 plants per person depending on how much you enjoy asparagus. You do the math!

Mature asparagus can reach 5-feet in height

PLANTING THE CROWNS

Do not plant the crowns too close together. It won’t be an issue for a while, but you need to think long-term to when the asparagus plant has been growing in the bed for 20 years! 

Plants should be spaced about 12 to preferably 18 inches apart in rows. If space permits, 5 feet between rows is optimal to prevent fungal diseases. Dig a trench or furrow about 6 to 12 inches wide for each row. (This modern method of asparagus cultivation has largely replaced the old method of digging an 18-inch trench and backfilling it.)

Add some organic starter fertilizer to the furrow to give your plants a good start. Being perennial, you only get one chance to fortify the root zone, so don’t skimp on this step.

Slightly mound the soil in the trench—the top of the mound will be about 3 inches below the soil surface.

Position the bareroot plant with the bud facing upwards on top of the mound. Gently spread the roots out into the trench. Cover the trench with soil and firm in gently to remove air pockets.

WATERING ASPARAGUS

Give your newly planted asparagus crowns a good, deep soaking immediately after planting. Once established, weekly water applications that wet the soil to a depth of 8 inches should suffice. Increase watering during dry, hot periods.

FEEDING ASPARAGUS

Asparagus is regarded as being a heavy feeder. As such, it needs all the food it can get in order to produce strong spears.

Select a balanced, organic formula with equal parts nitrogen, phosphorus and potassium, such as a 10-10-10 or 15-15-15.

Regular fertilization during the first three years following planting is key to ensuring healthy root development and plant growth. Fertilize in early spring as the new growth appears

Mature asparagus plants have similar nutrient requirements as young plants, but they require a later application. Beginning in the fourth year, apply fertilizer after the final harvest in late spring or early summer. This is because harvesting the stalks triggers the plant to produce new growth, which takes a lot of energy—so this is the time to feed the mature asparagus plant.

When applying fertilizer, avoid direct contact with the asparagus plant.

Always water the plants well immediately after fertilizing to ensure that any traces of fertilizer are washed off the leaves. This will also direct the fertilizer to the roots where it’s needed.

HARVESTING ASPARAGUS

Harvesting begins in early spring and lasts for about a month till late spring/early summer at which point the spears will become considerably thinner.

On a well-grown plant, you should be picking 7 to 9-inch spears. Interestingly, the diameter of the spear has no bearing on its quality.

Asparagus is best picked when the bud is still closed. The more the tip opens, the less tasty and tender will be the spears. The best time to harvest asparagus is in the morning. If you leave it too late on a warm day, you will see them practically grow in front of your eyes!

Asparagus spears are best picked when they are young

You can either snap the spear off where it naturally bends at the base of the spear, or use a knife to sever the stalk just below the soil line.

The spears should be supple and crisp; never limp or pliable. Similarly, they should be either green or purple depending on variety; any other color indicates damage of some nature, possibly frost damage.

At the start of the season, you will probably harvest between 7 to 9 spears ever two to four days.  As it warms up, the plant produces spears more vigorously and you should be able to harvest once or twice per day. Expect about 24 harvests per season.

As the harvesting season ends, spears are allowed to fern—the spears will grow, and the fronds (ferns) will unfurl from the spears. Mature asparagus can produce fern fronds 5 feet or taller. This fern-like foliage will feed the roots for next year’s crop.       

Asparagus fronds begin to unfurl

Resist the temptation to harvest your asparagus spears too early. Most authorities recommend waiting three years before harvesting. Certainly, don’t harvest them the first year and if you must try a few spears in the second year, do so sparingly. Essentially, the young plants are putting down their foundation. Think long-term!          

STORING ASPARAGUS SPEARS

Always store asparagus spears facing the same way to avoid damaging the delicate tips. Sprinkle a little water on the cut end (not the tip) to rehydrate it. Refrigerate by storing the spears in plastic or paper bags to avoid dehydration. They should last up to two weeks in the fridge.

ASPARAGUS PESTS

The worst culprit is the asparagus beetle which is orange to orange-red and black. They attack asparagus tips and ferns and lay eggs along the spears which hatch into larvae.

This beetle is most active in the afternoon and can be removed by handpicking and dropped in a soapy-water solution.

Alternatively, spray with organic sprays such as Neem oil. Better still, use natural predators such as ladybugs (aka ladybirds). Beneficial nematodes are also highly effective in eradicating these pests and offer a chemical-free solution to these pests.

Asparagus beetles

MAINTENANCE

Weeding: Even though there will initially be plenty of room between the plants, avoid interplanting.  Ensure that you keep the asparagus bed weed-free; competition for nutrients will reduce both the quantity and quality of your asparagus crop.

Pruning: Once the foliage begins to yellow and eventually brown, you can cut it back (unless you’re waiting to sex your plants) to about 4 inches above soil level, but do not prune prior to die-off— while the plant is still green. Pruning the foliage is regarded as a good maintenance policy as it lowers the risk of Asparagus beetle. Also, unless you want to collect seed, do not allow your female plants to go to seed, as this process consumes a lot of energy.

Mulching: After pruning the foliage, apply an annual thick layer of top dressing of compost and/or manure to amend the soil mix by adding nutrients which will replenish the soil. A layer of straw is helpful too, as are decayed leaves and bark. Additionally, this will also retard weed growth and protect the crowns through the winter months, especially in zones where temperatures dip to below freezing. New spears will simply push through the mulch in the spring.      

TRANSPLANTING ASPARAGUS

Remember asparagus resents root disturbance. However, if you must relocate your plants, do so in the early spring while the plants are still dormant, or before the first fall frost in late fall after the foliage has been cut back.

Carefully lift the crowns. Avoid disturbing the roots. If necessary, divide the root clump into two or more sections and transplant. Water well. Ensure that you harvest sparingly the following year.

The promise of a healthy crop of asparagus

These tips on managing and caring for your asparagus plants will ensure a healthy crop for many years to come, giving you a serious return on your initial investment. Go asparagus!

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