Asparagus in Zone 5B — Mountain West

Asparagus is a true treat in the Mountain West garden. There's nothing quite like the taste of freshly harvested spears, grilled with a bit of olive oil and salt. Plus, asparagus is incredibly versatile in the kitchen, and the satisfaction of harvesting your own after a couple of years is hard to beat.

High altitude gardening definitely presents its challenges, including intense sun and our short 149-day growing season. But with careful timing and the right techniques, you can absolutely enjoy homegrown asparagus. We'll help you navigate our unique climate and get the most out of your patch.

Transplant your asparagus crowns outdoors from early to mid May, once the risk of hard frost has passed. Before planting, be sure to harden off your asparagus crowns by gradually exposing them to outdoor conditions for about a week. This prevents shock from our intense sun.

Space the crowns 18-24 inches apart in well-drained soil. Keep an eye on the weather forecast around transplant time. Late-season snow or a sudden cold snap can still happen, so be ready to cover your young plants if needed. Remember, buy 1-year-old crowns; starting from seed will add years before you get your first harvest.

Asparagus needs moderate watering, especially in the first two years while it's establishing its deep root system. Even though it's drought-tolerant once established, our dry Mountain climate means you'll still need to pay attention to watering, especially during the hottest parts of the summer.

During the peak growing season, aim for about 1 inch of water per week, either from rainfall or irrigation. Use the "finger test" to check the soil moisture: stick your finger about 2 inches deep near the base of the plant. If the soil feels dry, it's time to water. Focus on watering at the base of the plant to avoid wetting the foliage, which helps prevent fungal issues in our low-humidity environment.

Signs of underwatering include wilting or yellowing spears. Overwatering, on the other hand, can lead to crown rot, so make sure your soil is well-draining. A layer of mulch, like wood chips or straw, can help retain moisture in the soil and regulate soil temperature, which is especially helpful with our cool nights.

Asparagus pruning is pretty minimal, which is great for us busy Mountain gardeners! The most important thing is to let the ferns grow freely all summer long. These ferns are essential for feeding the crown and ensuring a good harvest next year.

In late fall, after the ferns have turned brown and died back from the first frost (around early October in the mountains), or in early spring before new growth emerges, you can cut them back to ground level. Also, remember not to over-harvest your asparagus. Limit harvesting to a maximum of 8 weeks per season to allow the plants to replenish their energy stores.

You can expect your first asparagus harvest in early May through mid October, typically about two years after transplanting crowns. Look for spears that are 6-8 inches tall with tight, compact tips. These are the most tender and flavorful.

To harvest, snap the spears off at ground level. Avoid cutting them, as this can damage the crown. Continue harvesting regularly as new spears emerge, but remember to stop harvesting when the spears start to become thin (about pencil-width). This signals that the plant needs to focus on building up its reserves for the following year.

As the growing season winds down and the first frost approaches, stop harvesting altogether and let all the remaining spears fern out. This will ensure a healthy and productive asparagus patch for years to come.

Asparagus can be relatively easy to grow, but here are a few common problems we see in the Mountain West:

Asparagus Beetle

• What it looks like: Small, elongated beetles (often striped or spotted) and their larvae feeding on spears and ferns. You might see chewed leaves and brown or yellow eggs attached to the spears.
• What causes it: These beetles are attracted to asparagus plants. Our intense sun can stress plants, making them more susceptible.
• How to fix/prevent it: Handpick beetles and larvae when you see them. Encourage beneficial insects like ladybugs. Insecticidal soap can be used as a last resort.

Crown Rot from Poor Drainage

• What it looks like: Yellowing or wilting spears, stunted growth, and a mushy, decaying crown.
• What causes it: Overwatering or poorly draining soil. Our alkaline soil can sometimes contribute to drainage problems.
• How to fix/prevent it: Ensure your asparagus bed has well-draining soil. Avoid overwatering. Amend heavy clay soils with compost and organic matter.

Thin Spears from Over-Harvesting

• What it looks like: Spears that are consistently thin and weak, even early in the season.
• What causes it: Harvesting too many spears for too long, depleting the plant's energy reserves.
• How to fix/prevent it: Limit your harvest to 8 weeks per season. Stop harvesting when spears become pencil-thin. Let the plants fern out to replenish their energy.

Mountain West Specific Challenges: Our moderate-at-altitude summer heat and low humidity generally mean fewer fungal problems for asparagus compared to other regions. However, the dry rainfall can necessitate consistent watering, and our alkaline soil may require amending with compost to improve drainage and nutrient availability. Hail can also damage young spears and ferns, so consider using netting if hailstorms are frequent in your area.

Companion planting can be a great way to improve your asparagus patch in the Mountain West.

• Tomato, parsley, basil: Tomatoes are good companions because they release solanine, which can repel asparagus beetles. Parsley attracts beneficial insects that prey on asparagus beetle larvae. Basil also repels asparagus beetles and other pests.
• Onion, garlic: Avoid planting asparagus near onions or garlic. These plants can inhibit asparagus growth, possibly due to allelopathic compounds they release into the soil.