7 Reasons Why Your Asparagus Spears Are So Thin

Is it your first time growing asparagus spears, and you feel disappointed by the quality of your harvest? Or maybe you’re a seasoned gardener but can’t figure out why your asparagus spears seem thinner than normal this year. Then, this article is for you.

Your asparagus spears could be thin because you harvested them too early. Asparagus plants need 1-2 years to establish themselves and produce good-quality spears. You may have also been growing female plants, which are generally thinner than male plants. Plant stress can also contribute to poor yield.

In this article, I’ll give you 6 reasons why your asparagus spears are so thin and mention some strategies you can utilize to save this year’s harvest or improve the next one. Keep reading to learn more!

Overview of Asparagus Anatomy

Asparagus is a perennial flowering plant highly valued for its spears. The spears are succulent stems widely used for cooking or in vegetable salads.

That said, good-quality asparagus spears shouldn’t be thin. They’re usually harvested when they reach 7-9 inches (18-23 cm) long and 5/16 inches (8 mm) in diameter. All-male asparagus hybrids tend to have thicker stems than female plants.

So if your spears appear long but spindly, it could be caused by certain environmental stressors. A plant under stress won’t produce its best crop because it will have to devote much energy to damage repair. Other possibilities include poorly timed harvest and growing female asparagus plants.

Let’s explore the reasons for thinner asparagus spears below.

1. Harvesting Too Early

Novice asparagus growers might feel disappointed after their first harvest consists of thin, spindly asparagus spears. However, that shouldn’t be a cause for concern.

Asparagus plants need at least a few years of growth to mature and produce full-sized veggies. Avoid harvesting any spears in the first 1-2 years. Your asparagus plant will need initial spears to develop into ferns to carry out photosynthesis.

Most asparagus plants will reach their potential output by the time they’re 3-4 years old. You can then begin plucking spears off the plant. 

I know this may be disappointing news if you were expecting your newly made asparagus bed to yield you full-sized veggies from the get-go.

But on the bright side, asparagus plants produce veggies for over a decade after they are mature. Some plants survive as long as 30 years. So, once things are in motion, you can expect to harvest annually for years to come.

2. Male Vs. Female Asparagus Productivity

Asparagus plants are dioecious and produce distinct male and female plants. Plant sex plays a slight role in determining when the plant reaches maturity and how thick the spears will be.

Female plants need to produce seeds, so they aren’t able to give spear production their 100%. Male plants don’t bear seeds, so they can produce more abundant and thicker spears. 

If you’re looking for thicker spears, opt for an all-male variety, such as Erasmus and Jersey Giant.

Only female plants produce berries, so if you discover that you have an all-female or mixed variety, you can improve your asparagus bed’s yield gradually by replacing female plants with male plants. Note that established asparagus plants have deep roots and don’t respond well to transplanting, so replacing them is going to be a long-term process.  

3. Improper Watering

One of the common reasons for a thin harvest is improper watering, which can have devastating consequences. 

According to the University of Minnesota, asparagus beds should receive at least 1 inch (2.5 cm) of water per square foot (0.09 sqm) of soil weekly. This can be taken care of by rainfall if you’re in a rainy region. Otherwise, you will have to make up the difference.

Note that younger plants need more water, up to 2 inches (5 cm) weekly. 

Now, those are general guidelines. You can adjust greatly based on your local conditions influenced by temperature, humidity, and wind. 


We know that all plants need water to thrive. Asparagus is no different. A lack of water will slow growth considerably and have worse effects if left unaddressed. 

Asparagus plants are somewhat drought-tolerant. They’ll be fine if you forget to water them for a week or two. However, prolonged dehydration will take its toll on the plant and affect the thickness of the spears it will produce. 

If you live in a particularly hot or dry region, your asparagus bed is more likely to suffer from underwatering. You could water more frequently, say twice a week, to compensate for the increased water loss. 

You can also apply 2 inches (5 cm) of loose organic mulch, such as straw or pine needles, to prevent the soil from drying out too quickly.

I also recommend watering your asparagus bed deeply. Asparagus crown is rather deep within the soil, so watering the surface alone won’t be enough. 

You don’t need to water your asparagus bed after the plants die off in winter. They’ll need a period of dormancy during the winter to come back strong after the frosty temperatures blow over. 


Overwatering is a menace for plants because it leads to root rot. When plant roots are engulfed by water, they cannot access life-sustaining oxygen. If they keep standing in water long enough, they’ll die and begin to rot. 

Your asparagus plant’s crown is usually buried at least 6 inches (15 cm) deep, making it susceptible to rot. You can prevent your asparagus plants from being overwatered by waiting another day or two after the top 2-3 inches (5-7.6 cm) of soil dries out

Poor Drainage

Overwatering in a garden bed is usually caused by poor drainage. Use high-quality soil that has a good capacity for moisture retention but doesn’t prevent water from draining entirely. 

A great way to naturally improve your soil’s drainage is by mixing in some compost. The organic matter helps retain enough moisture for the plant’s roots to absorb while draining the excess because of its porosity.

If you’re growing your asparagus in raised beds, there’s a lower risk of soil compaction due to foot traffic. You can add compost to the upper 2 inches (5 cm) of the soil in early spring to maintain good drainage and supply a slow release of nutrients before the spears come out.

On the other hand, in-ground asparagus beds need protection from foot traffic. Keep this in mind when planning your garden bed. You can place cardboard or straw mulch along pathways between plant rows to prevent compaction within the plant’s root zone.

4. Not Enough Sunlight

According to the University of New Hampshire, asparagus plants need at least 8 hours of sunlight a day

A sun-deprived asparagus plant ends up being malnourished and undergrown. It will also forego horizontal growth in favor of vertical growth to grow taller and (hopefully) acquire more exposure to the sun. This can cause your asparagus spears to end up long, thin, and spindly. 

Don’t worry about setting up a means for shade (unless it’s really hot where you live), and let your asparagus bed bask in direct sun all day. The plant can survive in dappled sun or light shade but the spears will be smaller during harvesting time. 

The benefits of sun exposure extend beyond plant or crop size. UV-rich sunlight decreases the likelihood of your asparagus bed contracting a disease or being infested by pests. Fungus, in particular, is less likely to grow where the sun shines. 

5. Poor Soil Quality

Various soil-based problems can prevent your asparagus spears from growing to their potential size: 

Nutrient Deficiency

Growing new foliage, maintaining and repairing existing plant bodies, and producing spears is no trivial feat. It requires resources. These resources are made available to your plants in the form of nutrients in the soil. 

But these nutrients will decrease in concentration and run out over time, especially in an asparagus bed, which can survive for 30 years and doesn’t give you the opportunity for crop rotation. 

You’ll need to fertilize your asparagus bed regularly to keep up with your plants’ demands and keep their soil topped up with nutrients.

You can use standard all-purpose fertilizer for this purpose. A 10-10-10 NPK fertilizer is perfect since the asparagus plant needs all three equally as much for healthy growth. 

Compost is a great option, too, since asparagus prefers its growing medium to be rich in organic matter. 

Fertilize after the last winter frost, when the growing season just begins. This will allow your asparagus plants to reap the benefits of the extra nutrients in the soil for a full growing season. 


Fertilization is essential to keeping your asparagus plants healthy and obtaining better harvests. However, adding too much fertilizer to the soil will increase its nutrient concentration to toxic levels

According to Iowa State University, you should use 1 to 1.5 pounds (0.45-0.68 kg) of fertilizer for every 100 square feet (9.3 sqm) of your asparagus bed. 

It also helps if you do a soil test every 1-2 years to check the nutrient levels and ensure that you’re not over-fertilizing your asparagus bed.

Unsuitable Soil pH

Your asparagus bed should have a slightly acidic soil pH of 6.5 to 6.8. This is the optimal pH for asparagus and is most conducive to growth. Outside of this pH range, the plant will have difficulty absorbing soil nutrients. 

So you could have a fertile growing medium for your asparagus plants, but if the pH is unsuitable, the plants will end up unhealthy and malnourished. 

You can use a pH testing kit to measure your soil pH at home.

Compacted Soil

Compact soil is extremely dense soil that is problematic due to multiple reasons. 

  • It prevents water from draining away, leading to root rot and many fungal diseases.
  • It prevents air circulation, suffocating the roots and making them more vulnerable to rotting.
  • It restricts root growth. Compacted soil is often so dense that roots can’t grow through it

Asparagus plants should never be grown on compacted soil. The bed should be positioned on a patch of land that has healthy, well-draining soil. 

6. Overabundance of Weeds

Weed growth is a major concern when growing asparagus. Weeds compete with your plants for resources. If they overpopulate your asparagus bed, they’ll deprive your plants of the vital nutrients they need to survive. 

If you have a smaller asparagus bed, I suggest you remove any weeds you spot by hand.

It’s best to check for and eliminate new growths on an ongoing basis since removal by hand becomes harder the longer the weed is allowed to grow and form a support structure. 

If you’re struggling with weed management, you can also use fertilizer after the last harvest, as we discussed above. 

Applying organic mulches like straw, pine needles, or cardboard is also effective in suppressing weeds while preventing compaction and improving moisture retention.

Pro tip: Do not use salt or chemical herbicides. They may kill weeds, but they will hurt your asparagus plants and yield, too. 

7. Incorrect Care and Growing Practices

Unhappy and stressed plants won’t produce satisfactory yields. This translates to your asparagus plants having few and thin spears.

Here are some common mistakes novice gardeners make when planting asparagus for the first time:

Not Planting Deep Enough

Unlike seeds, crowns need to be planted deep into the soil. Planting them too close to the surface will lessen their ability to obtain sufficient nutrients and water from the soil. 

The type of soil used influences how deep you should plant the crown. For example, with sandy soil that drains water away quickly, it’s best to plant the crown 10-12 inches (25-30 cm) deep

With clayey soil that can hold water far better, you can get away with planting the crown 6-8 inches (15-20 cm) deep

Also, the crowns aren’t meant to be covered with soil immediately after planting. The plant needs vegetation on the surface at all times. Wait a few weeks for some initial growth to occur, and cover the crown with soil gradually over that time. 

If you didn’t plant your asparagus crowns deep enough, you could compensate by covering the base of the plant with a few extra inches of soil. 


Asparagus plants have a large root system. They will compete with each other for resources if planted too close together. 

To avoid overcrowding, make sure to give your plants plenty of space. I recommend planting crowns in a row 2 feet (0.61 m) apart. However, if you’re short on space, the minimum acceptable spread is 18 inches (45 cm)

Rows should be 4 to 6 feet (1.2-1.8 m) apart. Initially, this may look like a lot of wasted space, but your asparagus will grow to occupy that space. 

Early Pruning

Pruning during the growing season is important. You should keep your asparagus plants trimmed and free of dead, damaged, and decaying foliage during this period. 

Don’t cut back your asparagus ferns immediately after the last harvest. Leaving the ferns be will allow the plant to continue carrying out photosynthesis until they die due to the cold naturally. You can then cut back the dead foliage.

The extra few weeks of photosynthesis equate to a healthier asparagus plant better equipped to survive the winters and produce a plentiful harvest next year. 

Care Tips and Growing Practices for Thicker Spears

We’ve discussed, in detail, the potential reasons that might be causing your asparagus spears to be thin. Let’s now talk about what you can do to grow thicker spears. 

Buy a Variety Known for Thick Spears

The best variety for thicker spears is an all-male hybrid, such as the Jersey series (Giant, Knight, and Supreme). Unfortunately, the producers of these hybrids stopped breeding them so there’s limited supply in the market.

Here’s a list of other male asparagus hybrids famous for thicker spears:

  • Apollo
  • Atlas
  • Erasmus
  • UC157
  • Millenium

You can also improve the crop yield of your current bed by gradually replacing the female plants with male plants. 

Water Properly

Make sure you’re watering your asparagus plants properly. As mentioned before, asparagus plants need an inch (2.5 cm) of water per square foot (0.09 sqm) per week.

This is just a general guideline, so you’ll need to adjust based on visual factors, such as how dry your topsoil is, and the climate in your area.

Use Well-Draining Soil

Use well-draining soil for your asparagus bed. You can improve your soil’s capacity for water drainage by mixing in compost. Compost also doubles as an organic, slow-release fertilizer, so it’s very beneficial for your asparagus plants. 

Provide Enough Sunlight

Ensure your asparagus plants are receiving enough sunlight. Remember: they need at least 8 hours of direct sunlight daily. It’s best to have your asparagus bed in a spot that doesn’t receive shade. 

Address Any Problems With the Soil

Follow an annual fertilization plan to maintain nutrient levels in the soil. It’s best to fertilize at the beginning of the growing season (early spring).

Let them Die Off on Their Own

Leave your asparagus ferns until they die off on their own when winter sets in. They’ll help carry out photosynthesis in the last few weeks of their life, improving your next year’s harvest.

You can cut your asparagus plant back to the ground once the ferns die off. 

Final Thoughts

Your asparagus spears may be thin simply because your plants aren’t mature enough to produce a full-sized crop. If you have adult plants, the thin spears are likely caused by environmental stress. 

These are the common culprits behind thin spear growth:

  • Inappropriate watering
  • Inadequate exposure to sunlight
  • Problems with the soil, such as a nutrient-deficiency
  • Excessive weed growth
  • Poor care practices

Addressing these problems will help your asparagus plants grow thicker, fuller, healthier spears.

Dr. Moritz Picot

Dr. Moritz Picot is a horticulture enthusiast and the founder of TheGrowingLeaf.com, where he serves as the lead content writer. He established the website in 2022 as a valuable resource for both gardening aficionados and beginners, compiling all the gardening tips he has accumulated over the past 25 years. Alex has a passion for nurturing plants, transforming backyards into inviting spaces, and sharing his knowledge with the world.

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