Why Are Your Asparagus Spears So Thin? 6 Reasons

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. This article is for you.

Your asparagus spears could be thin due to improper watering, soil problems, insufficient sunlight, incorrect care practices, pests, disease, and other poor environmental conditions. Asparagus plants need a few years of growth and adequate care before they can produce their best crop. 

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 if that interests you.

6 Reasons Why Your Asparagus Spears Are So Thin

Asparagus spears aren’t supposed to be thin. Even though most commercial spears will look like they could snap in two under their own weight, homegrown spears will be thick, sizable, nutritious, and super healthy–assuming nothing goes wrong during the growing process, of course. 

Certain problems that go unnoticed can cause an entire season’s worth of produce to turn out thin and spindly. Most of these problems can be considered, in one way or another, environmental stress. 

A plant under stress won’t produce its best crop because it has to dedicate energy and resources to damage repair.

So, why are your asparagus spears so thin?

1. Your Asparagus Plants Are Too Young

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. 

It’s best not to harvest any spears in the first year or two. 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 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.

Plant Variety

I should also quickly mention that plant variety plays a slight role in determining when the plant reaches maturity and how thick the spears will be.

Of course, you should choose a variety known to produce thick spears. 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 much more spears. 

As a result, the best varieties are now male-dominated, with some being all male. Erasmus and Jersey Giant are just two examples of varieties that feature mostly male plants and grow large spears in plenty. 

You’re stuck with the variety you have, but you can improve your asparagus bed’s yield gradually by replacing female plants with male plants. As you can probably imagine, this is a long-term process. 

Only female plants produce berries, so you’ll know which ones to go after. 

2. You Aren’t Watering Your Asparagus Plants Properly

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 one inch (2.54 cm) of water per square foot (929 sq cm) 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 – 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. 

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

I should also mention that you don’t need to water your asparagus bed after the plants die off. 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 also susceptible to root rot. You can prevent your asparagus plants from being overwatered by letting the soil dry out between waterings. 

And I don’t just mean the surface of the soil. There’s still plenty of water down below. Therefore, it’s best to wait another day or two after the top layer 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.

3. Your Asparagus Plants Aren’t Receiving Enough Sunlight

Plants need sunlight to carry out photosynthesis. This is an essential, life-sustaining biological process that converts nutrients gathered from the soil into food the plant can consume. 

A sun-deprived plant, therefore, 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. 

Shady locations are out of the question, but how much sunlight should an asparagus bed be exposed to? According to the University of New Hampshire, asparagus plants need at least 8 hours of sunlight a day

Don’t worry about setting up a means for shade (unless it’s really hot where you live), and let your asparagus bed see the direct sun all day. 

The plant can survive in dappled sun or light shade but will grow smaller and produce smaller and fewer veggies 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. 

4. There Are Problems With the Soil

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

A Nutrient Deficiency

Growing new foliage, maintaining and repairing existing plant body, 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. 

It’s also possible to fertilize asparagus after the last harvest. This is slightly less effective in terms of making the nutrients available to the plant when it most needs them, but it’s a common practice and for a good reason. 

Fertilizing early in the growing season strongly encourages weed growth. Weeds compete with your asparagus for nutrients. By fertilizing later in the year, you ensure the soil stays relatively nutrient-rich all year round without having to deal with excess weeds. 


Fertilization is essential to keeping your asparagus plants healthy and obtaining better harvests. However, there is such a thing as over-fertilization. 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 (9.29 square meters) of your asparagus bed

As long as you stick to this range, you’ll likely be fine. In fact, you’ll probably be fine even if you go slightly over since some experts suggest using up to 2.5 pounds (1.13 kg) per 100 square feet (9.29 square meters)

I recommend taking the more conservative approach in this case, though. 

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 very fertile growing medium for your asparagus plants, but if the pH is too extreme, they’ll 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 similar problems. 
  • 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. 

5. Weeds Are Depriving Your Asparagus Plants of Nutrients

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. 

In larger asparagus beds, employing herbicide to eliminate weeds becomes a necessity. I would avoid using herbicides if possible, but there are plenty of safe and effective mixtures out there. 

Pro tip: Do not use salt. It may kill weeds, but it will hurt your asparagus plants too. 

6. 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 12 inches (30 cm) deep

With clayey soil that can hold water far better, you can get away with planting the crown 6 inches (15 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 two feet (60 cm) 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

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. 

Now, that doesn’t mean pruning during the on-season isn’t important at all. You should keep your asparagus plants trimmed and free of dead, damaged, and decaying foliage during the growing season. 

What You Can Do To Harvest Thicker Asparagus 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 that’s known to produce thick spears. This will likely be a male-dominated variety of asparagus. You can also improve the crop yield of your current bed by gradually replacing the female plants with male plants. 
  • Make sure you’re watering your asparagus plants properly. As mentioned before, asparagus plants need an inch (2.54 cm) of water per square foot 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. 
  • 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. 
  • 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). However, late summer fertilization is the better option if you’re struggling with weed management. 
  • Leave your asparagus ferns be 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.

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

Recent Posts