Asparagus in Zone 10B — Desert Southwest

Asparagus is a worthwhile addition to your Desert Southwest garden. The fresh, homegrown flavor is far superior to what you find in stores. Plus, its versatility in cooking and the sheer satisfaction of harvesting your own spears make it a rewarding crop, especially when you consider our mild winters.

While our region presents unique challenges like extreme heat and alkaline soil, growing asparagus is manageable with careful timing and proper techniques. Our long, 349-day growing season gives you a great head start. You just need to get it right.

The ideal time to transplant asparagus crowns in our area is mid to late January. This gives the plants time to establish before the intense summer heat hits. Before planting, harden off your asparagus crowns by gradually exposing them to outdoor conditions for about a week.

Plant the crowns 18-24 inches apart in well-draining soil. Remember that our winters are short. The goal is to get your transplants established before the weather heats up in late spring. Buy one-year-old crowns for best results, as starting from seed extends the time to harvest by several years.

Established asparagus is fairly drought-tolerant due to its deep root system, but consistent watering is crucial, especially during the first two years. During the cooler months, water deeply about once a week, providing about 1 inch of water. Use the "finger test"—stick your finger about 2 inches into the soil; if it feels dry, it's time to water.

As temperatures rise in late spring, increase watering frequency to 2-3 times per week, providing about 2 inches of water each time. During the monsoon season, adjust your watering schedule based on rainfall. Water at the base of the plants to avoid wetting the foliage, as our arid climate still allows for some fungal issues if the plants stay wet for too long.

Signs of underwatering include yellowing or wilting ferns, while overwatering can lead to root rot. A layer of organic mulch around the base of the plants helps retain moisture and regulate soil temperature, which is especially helpful in our extreme heat.

Asparagus requires minimal pruning. The key is to let the ferns grow and flourish throughout the summer. These ferns are vital for storing energy in the crown, ensuring a good harvest next year.

Once the ferns die back in late fall or early spring, cut them down to ground level. This removes any potential overwintering pests or diseases. Remember to limit your harvest period to no more than 8 weeks each season to avoid weakening the plants.

You can expect your first harvest of asparagus spears around mid-January, about two years after transplanting the crowns. Look for spears that are 6-8 inches tall with tight, unopened tips. These are the most tender and flavorful.

To harvest, snap the spears off at ground level. Avoid cutting, as this can damage the crown. Continue harvesting spears as they emerge, but stop when the spears become thin and pencil-like. This indicates that the plant needs to replenish its energy reserves. Let the remaining spears fern out to nourish the crown for the next season.

As the first frost approaches in late December, the fern will turn yellow and die back. This is a natural process. Cut the dead foliage off at ground level.

Here are some common problems you might encounter growing asparagus in the Desert Southwest:

Asparagus Beetle

• What it looks like: Small, elongated beetles and their larvae feeding on spears and ferns, causing damage and discoloration.
• What causes it: These pests thrive in warm weather and can quickly infest asparagus plants. Our long growing season provides ample opportunity for multiple generations.
• 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, but apply carefully to avoid harming pollinators.

Crown Rot from Poor Drainage

• What it looks like: Yellowing or wilting ferns, stunted growth, and mushy, decaying roots.
• What causes it: Our alkaline soil and caliche layers can hinder drainage, especially during monsoon season, leading to root rot.
• How to fix/prevent it: Ensure your planting site has well-draining soil. Amend heavy clay soils with organic matter to improve drainage. Avoid overwatering, especially during the monsoon. Consider raised beds if drainage is a persistent issue.

Thin Spears from Over-Harvesting

• What it looks like: Spears that are significantly thinner than usual, often pencil-thin.
• What causes it: Depleting the plant's energy reserves by harvesting for too long or too frequently.
• How to fix/prevent it: Limit your harvest period to 8 weeks per season. Let plenty of spears fern out to allow the plant to store energy for the following year. Provide adequate water and fertilizer to support healthy growth.

Desert Southwest Specific Challenges Our extreme heat can stress asparagus plants, especially during the establishment phase. Provide afternoon shade with shade cloth if necessary. Arid humidity can also lead to increased pest pressure, so monitor plants regularly. The monsoon rainfall can be a blessing, but be mindful of potential drainage issues and adjust watering accordingly.

Companion planting can benefit your asparagus. Tomatoes, parsley, and basil are good companions. Tomatoes provide shade during the hottest part of the day, protecting asparagus from sunscald. Parsley attracts beneficial insects that prey on asparagus pests. Basil repels asparagus beetles.

Avoid planting asparagus near onions and garlic, as they can inhibit asparagus growth. These alliums release compounds into the soil that can stunt the growth of asparagus. Keep your asparagus patch separate from these plants for best results.