Asparagus in Zone 4B — Mountain West

Asparagus is a worthwhile investment for the Mountain West gardener. The fresh, homegrown flavor is far superior to anything you'll find at the store, and its versatility in cooking is unmatched. Plus, there's a unique satisfaction in harvesting spears from a plant that can thrive for decades in your garden.

Yes, high altitude gardening presents challenges like intense sun and a short season. But asparagus is very hardy. With proper timing and care, you can successfully grow asparagus here, even with our roughly 128-day growing season.

Transplant your asparagus crowns outdoors from mid to late May, once the danger 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 helps them adjust to the intense sun and fluctuating temperatures common in our Mountain climate.

Space the crowns 18-24 inches apart in well-draining soil. Remember, you're planting for the long haul, so choose a location where they'll have plenty of room to spread. It's best to start with 1-year-old crowns. While you can grow from seed, it adds years to your first harvest.

Established asparagus is fairly drought-tolerant thanks to its deep root system, but consistent watering is key, especially during our dry Mountain summers. During the first two years after transplanting, water deeply about once a week, providing roughly 1 inch of water. Use the finger test: if the soil feels dry to a depth of 2 inches, it's time to water.

After the initial establishment period, adjust your watering schedule based on rainfall. With our low humidity, it's best to water at the base of the plants to avoid creating conditions that could lead to fungal issues. Overhead watering is less of a concern here than in more humid climates.

Signs of underwatering include yellowing or wilting ferns, while overwatering can lead to crown rot. Mulching around your asparagus plants with a layer of compost or straw helps retain moisture and regulate soil temperature, which is particularly beneficial in our environment.

Asparagus requires minimal pruning, and what you do prune is very important. The most important thing is to let the ferns grow freely throughout the summer. These ferns are essential for photosynthesis, providing energy to the crown for next year's spears.

In late fall, after the first frost around mid- September kills the ferns, or in early spring before new growth emerges, cut back the dead ferns to ground level. Also, be mindful of your harvest: don't harvest for more than 8 weeks each season to avoid weakening the plants.

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

To harvest, simply snap the spears off at ground level. Avoid cutting, as this can damage the crown. Continue harvesting spears as they emerge, but stop when they become thin, about the width of a pencil. This signals that the plant needs to replenish its energy reserves.

As the first frost approaches in mid- September, stop harvesting altogether and allow the remaining spears to fern out. This will help the plant store energy for the following season's growth.

Here are a few common problems you might encounter with asparagus in the Mountain West:

Asparagus Beetle

• What it looks like: Small, elongated beetles (often orange and black) and their larvae feeding on spears and ferns, causing defoliation and stunted growth.
• What causes it: These beetles are attracted to asparagus plants, and our intense sun can exacerbate the damage they cause.
• How to fix/prevent it: Handpick beetles and larvae, use insecticidal soap, or introduce beneficial insects like ladybugs. Row covers can also provide a barrier.

Crown Rot

• What it looks like: Yellowing or wilting ferns, stunted growth, and a mushy, decaying crown.
• What causes it: Poorly drained soil and overwatering, which can be a problem during periods of heavy spring runoff or irrigation.
• How to fix/prevent it: Ensure good soil drainage by planting in raised beds or amending heavy clay soils with compost. Avoid overwatering, and consider using a fungicide if the problem persists.

Thin Spears

• What it looks like: Spears that are significantly thinner than usual, often pencil-thin or smaller.
• What causes it: Over-harvesting, which depletes the plant's energy reserves.
• How to fix/prevent it: Limit your harvest to 8 weeks per season, and allow plenty of spears to fern out to replenish the plant's energy.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity generally reduce disease pressure on asparagus. However, the intense sun can stress the plants, making them more susceptible to pests. Be sure to provide adequate water and consider using shade cloth during the hottest parts of the summer, especially for young plants.

Good companions for asparagus in the Mountain West include tomatoes, parsley, and basil. Tomatoes provide shade and support for asparagus ferns. Parsley attracts beneficial insects that prey on asparagus beetles. Basil repels asparagus beetles with its strong scent.

Avoid planting asparagus near onions or garlic. These plants are allelopathic, meaning they release chemicals that can inhibit asparagus growth. This is especially important to consider in our short growing season, where you want to maximize every plant's potential.