Yarrow in Zone 4A — Mountain West

Yarrow is a fantastic addition to any Mountain West garden. Its feathery foliage and clusters of colorful flowers add beauty, attract beneficial insects like crazy, and are even great for drying. Plus, the cool nights we get even in summer seem to intensify its fragrance and color.

Our high altitude and short growing season can make gardening tricky. But with Yarrow, you'll find it's surprisingly easy to manage if you get the timing right. With our 118-day growing season, you can get a good harvest if you start early enough.

Starting Yarrow indoors is an option, particularly if you want flowers in the first year. Begin in early to late March, about 8 weeks before you plan to transplant. This gives the seedlings a head start on our short season.

Use seed trays with a good seed-starting mix. Keep them warm (around 70°F) and provide plenty of light – a grow light is ideal, given our intense sun. Bottom watering is a great way to keep the soil moist without damping off. Remember, our late spring means you need to be patient and avoid setting them out too early.

Transplant your Yarrow seedlings outdoors in early May through early June, once the danger of hard frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents transplant shock under our intense UV.

Space them 12-18 inches apart. Keep an eye on the weather forecast; we can still get a late frost or even hail that time of year, so be prepared to cover them if needed. If you want blooms the first year, buying established starts from a local nursery is a great bet.

Direct sowing Yarrow is definitely doable in the Mountain West. Sow the seeds mid May through late June, when the soil has warmed up a bit. Choose a spot with full sun and well-drained soil.

Lightly rake the soil surface and sprinkle the seeds. Gently press them into the soil – they need light to germinate. Keep the soil consistently moist until the seedlings emerge. Thin them to 12-18 inches apart once they're a few inches tall. Direct sowing is easy, but keep in mind you likely won't get blooms in the first year.

Yarrow is incredibly drought-tolerant once established, which is a huge advantage in our dry Mountain climate. In general, less is more. Overwatering is a bigger threat than underwatering.

During the first few weeks after planting, water regularly to help them get established. After that, let the soil dry out between waterings. Stick your finger about 2 inches deep into the soil. If it's dry, it's time to water. Usually, about 1 inch of water per week is plenty, especially given our low humidity. Water at the base of the plant to avoid wetting the foliage.

In our climate, Yarrow is more likely to suffer from overwatering than underwatering. Yellowing leaves or floppy growth are signs you're giving it too much. A light layer of mulch can help retain some moisture, but be careful not to overdo it, as Yarrow prefers drier conditions.

Pruning Yarrow is simple and helps encourage more blooms. Deadhead spent flowers throughout the growing season, from late July through late September. This encourages a second flush of flowers before our first frost.

Simply snip off the flower heads just below the lowest petals. In the fall, after the first frost around mid- September, cut the plant back to its basal foliage (the leaves at the base). Yarrow can be aggressive, so divide the clumps every 2-3 years to keep it in check.

You can expect your first Yarrow harvest in late July through late September. The flowers are ready to harvest when they are fully open and their color is vibrant. This is also when they're most attractive to beneficial insects.

To harvest, simply cut the stems just above a set of leaves. For drying, hang the stems upside down in a cool, dark, dry place until they're completely dry. Regular harvesting encourages continued flower production throughout the season. Even as our first frost approaches in mid- September, you can often still get a few more blooms by cutting back any stems that look tired.

Yarrow is generally low-maintenance, but here are a few potential problems in the Mountain West:

Aggressive Spreading

• What it looks like: Yarrow can quickly spread via rhizomes, popping up in unwanted areas of your garden.
• What causes it: Our intense sun and well-drained soil create ideal conditions for Yarrow to thrive, sometimes a little *too* well.
• How to fix/prevent it: Plant it in a contained area or regularly divide the clumps to prevent it from taking over.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. The leaves might curl, yellow, and eventually die.
• What causes it: Powdery mildew thrives with warm days, cool nights, and moderate humidity. Ironically, dry leaf surfaces favor it, which can happen even with our low humidity if the air is stagnant.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning. Remove affected leaves promptly. Neem oil or potassium bicarbonate sprays can help. A milk spray (1 part milk to 9 parts water) is also effective.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. You might also see a sticky honeydew residue or curled, distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather. Ants often "farm" them for their honeydew.
• How to fix/prevent it: Knock them off with a strong spray of water. Encourage natural predators like ladybugs. Insecticidal soap or neem oil can be used for heavy infestations.

Mountain West Specific Challenges: Our intense UV light can stress plants, making them more susceptible to problems. However, our low humidity generally keeps fungal diseases like powdery mildew at bay. Just be sure to provide good air circulation and avoid overwatering.

Yarrow makes a great companion plant in the Mountain West garden. It attracts beneficial insects like ladybugs and hoverflies, which prey on pests that bother other plants.

Good companions include tomatoes and peppers, as Yarrow can help deter pests that attack these vegetables. Herbs like rosemary and thyme also benefit from Yarrow's presence. Strawberries are great companions, too, because Yarrow can improve their flavor and vigor. Avoid planting Yarrow near plants in the brassica family (cabbage, broccoli, kale), as it can sometimes attract cabbage moths.