Yarrow in Zone 7A — Desert Southwest

Yarrow is a fantastic addition to any Desert Southwest garden. Its feathery foliage and clusters of blooms add beauty, it attracts beneficial insects, and it's incredibly drought-tolerant – a must-have for our arid climate. Plus, you can dry the flowers for arrangements, extending your garden's beauty indoors.

Desert gardening presents unique challenges, but Yarrow is well-suited to our conditions. With careful timing, you can enjoy its beauty throughout our long, 230-day growing season. Focus on spring and fall planting to avoid the worst of the extreme heat.

Starting Yarrow indoors is an option, especially if you want a head start on blooms. Begin in early to late January, about eight weeks before you plan to transplant. Use seed trays with a well-draining seed starting mix and provide warmth (a heat mat is helpful) and plenty of light – a grow light works best.

Be sure to water from the bottom to avoid damping off. In our very-early spring, starting indoors allows you to get blooms the first year.

Transplant your Yarrow seedlings outdoors in mid-March through early April. This gives them time to establish before the extreme heat arrives. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Space plants 12-18 inches apart in a sunny spot. Keep an eye on the weather, as we can still get temperature swings during this time. Yarrow is a perennial, so if you want flowers the first year, buying starts may be your best bet.

Direct sowing Yarrow is a simple way to get it established in your garden. Sow seeds late March through late August, when the soil has warmed up. Prepare the soil by loosening it and removing any rocks or debris.

Yarrow prefers well-drained soil, so amend with compost if needed. Space seeds 12-18 inches apart. Keep the soil consistently moist until seedlings emerge. Direct sowing is easy, but you'll have to wait longer for blooms compared to starting indoors or using transplants.

Yarrow is a champion when it comes to water conservation, which is crucial in our Desert Southwest gardens. Once established, it's very drought-tolerant. In spring and fall, water deeply but infrequently.

Use the "finger test" – if the top two inches of soil are dry, it's time to water. Aim for about 1 inch of water per week, depending on rainfall. During our monsoon season, you may not need to water at all!

Water at the base of the plant to avoid wetting the foliage, which can encourage powdery mildew. In our arid climate, overhead watering isn't as big of a concern as it would be in humid regions, but it's still best to water at the base. Signs of underwatering include wilting and yellowing leaves, while overwatering can cause floppy growth. A light layer of rock mulch will help retain moisture and keep the soil cool.

Regular pruning keeps Yarrow looking its best and encourages more blooms. Deadhead spent flowers throughout the growing season to promote a second flush of color. Simply snip off the faded flower heads just below the bloom.

In the late fall, after the first frost around early November, cut the plant back to its basal foliage. This helps it conserve energy over the winter. Yarrow can be aggressive, so divide the clumps every 2-3 years to keep it in check.

You can expect your first Yarrow harvest from late May through mid November, about 65 days after planting. Harvest the flowers for drying when they are fully open and the colors are vibrant. Cut the stems just above a leaf node.

Hang the stems upside down in a cool, dark, and dry place to dry completely. Regularly harvesting flowers encourages continued production. Even as the first frost approaches in early November, you can still harvest any remaining blooms for drying.

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

Spreads Aggressively

• What it looks like: Yarrow can quickly spread beyond its intended area, forming dense mats and crowding out other plants.
• What causes it: Yarrow spreads through rhizomes (underground stems), which can quickly colonize new areas. This is exacerbated by our long growing season.
• How to fix/prevent it: Plant Yarrow in containers or raised beds to contain its spread. Regularly divide the clumps to prevent them from becoming too large. Deadheading flowers before they set seed also helps.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems, and sometimes fruit. Leaves curl, yellow, and die.
• What causes it: Various fungi that thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it. This is more common during our monsoon season when humidity increases.
• How to fix/prevent it: Improve air circulation through spacing and pruning. Remove affected leaves. Neem oil or potassium bicarbonate sprays help. Milk spray (1 part milk to 9 parts water) is surprisingly effective. Plant resistant varieties.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects. Populations explode in warm weather. Ant colonies may farm them for honeydew. Our warm springs and long growing season provide ample opportunity for aphid populations to build up.
• How to fix/prevent it: Strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer (it attracts them).

Desert Southwest Specific Challenges: Our extreme heat can stress Yarrow, making it more susceptible to pests and diseases. The arid humidity can also contribute to powdery mildew. However, Yarrow's drought tolerance makes it a great choice for our water-wise gardens. Just be sure to provide adequate spacing and monitor for problems regularly.

Yarrow is a great companion plant for many vegetables and herbs in the Desert Southwest. It attracts beneficial insects like ladybugs and lacewings, which help control pests on your tomatoes and peppers. It's also said to improve the flavor of herbs grown nearby.

Yarrow can be planted near strawberries, as it's thought to enhance their growth and disease resistance. Avoid planting Yarrow near plants that prefer very rich, moist soil, as it thrives in drier conditions.