Asparagus in Zone 8A — Desert Southwest

Asparagus is a worthwhile investment in your Desert Southwest garden. The tender spears are a culinary delight, far surpassing anything you'll find at the grocery store. Plus, the ferny foliage adds an elegant touch to your garden beds, offering a perennial beauty that thrives in our extended growing season.

Yes, we face extreme heat and alkaline soil here in the Desert Southwest. But by planting at the right time and providing adequate care, you can successfully grow asparagus. Our 265-day growing season allows for a long harvest window if you manage the plant's stress.

Transplant your asparagus crowns in early to mid March. This gives them a head start before the extreme heat arrives. Before transplanting, harden off your crowns by gradually exposing them to outdoor conditions for about a week.

Space the crowns 18-24 inches apart in well-draining soil. Keep an eye on the weather forecast; while asparagus is frost-hardy, a late cold snap after transplanting can still stress young plants.

Consistent watering is key, especially in our arid climate. While established asparagus is fairly drought-tolerant due to its deep roots, don't let it completely dry out, especially during the monsoon season when it's actively growing. Use the finger test: if the top 2 inches of soil feel dry, it's time to water.

During the hot summer months, give your asparagus about 1-2 inches of water per week, delivered deeply at the base of the plant. Avoid overhead watering, which can encourage fungal diseases even in our dry air, especially with the humidity spikes of monsoon season. In the cooler spring and fall, you can reduce watering to once every 10-14 days, depending on rainfall.

Signs of underwatering include wilting or yellowing ferns. Overwatering, on the other hand, can lead to crown rot, so ensure good drainage. A layer of organic mulch, like composted leaves or wood chips, helps retain moisture and regulate soil temperature, which is especially important during the extreme heat.

Asparagus requires minimal pruning. The most important thing is to allow the ferns to grow and flourish throughout the summer and fall. These ferns are essential for providing energy to the crown, ensuring a bountiful harvest the following year.

Once the ferns turn brown and die back in late fall or early spring (after our first frost around late November), you can cut them back to ground level. This clears the way for new growth in the spring. Remember to stop harvesting spears after about 8 weeks to allow the plant to replenish its energy reserves.

Your first substantial asparagus harvest will be in early March through early December, about two years after transplanting the crowns. Look for spears that are 6-8 inches tall with tightly closed tips. These are the most tender and flavorful.

To harvest, snap the spear off at ground level. Avoid cutting, which can damage the crown. Continue harvesting spears as they emerge, but stop when they start to thin to about the width of a pencil. At that point, let the remaining spears fern out to nourish the plant.

As the first frost approaches in late November, allow all remaining spears to fern out. This helps the plant store energy for the winter and ensures a better harvest next spring.

Here are a few common issues you might encounter growing asparagus in the Desert Southwest:

Asparagus Beetle

• What it looks like: Small, metallic blue or orange beetles and their larvae feeding on the spears and ferns, causing damage and discoloration.
• What causes it: These beetles thrive in warm weather and can quickly infest asparagus patches, especially during the spring and summer months.
• How to fix/prevent it: Handpick beetles and larvae when you see them. Encourage beneficial insects like ladybugs. In severe infestations, use neem oil, being careful to apply in the early morning or late evening to avoid leaf burn in our intense sun.

Crown Rot from Poor Drainage

• What it looks like: Yellowing or wilting ferns, stunted growth, and mushy, decaying crowns.
• What causes it: Crown rot is a fungal disease that thrives in poorly drained soil. Our alkaline soil and caliche layers can exacerbate drainage problems, especially during monsoon season.
• How to fix/prevent it: Ensure your asparagus bed has excellent drainage. Amend heavy clay soils with plenty of organic matter. Avoid overwatering, especially during periods of heavy rainfall. If crown rot is present, remove affected plants and avoid planting asparagus in that location for several years.

Thin Spears from Over-Harvesting

• What it looks like: Spears that emerge are significantly thinner than usual, sometimes no thicker than a pencil.
• What causes it: Over-harvesting depletes the plant's energy reserves. It does not have enough stored energy to produce healthy, thick spears.
• How to fix/prevent it: Limit your harvest to 6-8 weeks each year. Allow the remaining spears to fern out and replenish the plant's energy. Fertilize with a balanced fertilizer in the spring to support healthy growth.

Desert Southwest Specific Challenges: The extreme heat and intense sunlight of the Desert Southwest can stress asparagus plants, making them more susceptible to pests and diseases. Consistent watering and providing afternoon shade during the hottest months can help mitigate these effects. Also, our monsoon season's humidity spikes can create favorable conditions for fungal diseases, so good air circulation and well-drained soil are essential.

Companion planting can benefit your asparagus in the Desert Southwest. Tomatoes make excellent companions because they deter asparagus beetles. Parsley attracts beneficial insects that prey on asparagus pests. Basil also repels asparagus beetles and thrives in similar conditions.

Avoid planting asparagus near onions or garlic. These plants are allelopathic, meaning they release chemicals that can inhibit asparagus growth. Keeping these plants separate will help your asparagus thrive.