While lemon trees aren’t necessarily high maintenance, they do require the right conditions to thrive. A pest-free environment — with lots of sunlight and nutrient-rich soil — can be the key to this tree’s success. While there are several beneficial herbs and flowers you could grow alongside citrus in your garden, yarrow (Achillea millefolium) can be a particularly great way to ward off common pests attracted to lemon trees, while enriching the soil for hearty fruit production at the same time.

Yarrow is a perennial herb that presents a beautiful flat top of feathered flower clusters when fully bloomed. It has a high drought tolerance and prefers full sun and dry soil, and thrives in USDA Hardiness Zones 3 through 9, making it the perfect companion plant for lemon trees. When planted in the spring, the plant can bloom through summer and fall. Plus, yarrow flowers come in an array of colors that can create a beautiful floral arrangement for your garden. 

Some common citrus pests that could cause problems include aphids, mealybugs, and whiteflies. The damage typically caused by these bugs includes curled leaves, mold, and disease-damaged branches. They can even cause lower fruit yields or a decline in fruit quality. While yarrow itself is not a pest-repelling plant, it does attract beneficial insects like ladybugs, lacewings, tachinid flies, and hoverflies that eat problem bugs and therefore help control or reduce pest populations. Yarrow is also a nectar-rich plant that attracts a variety of pollinators like sweat bees, butterflies, and parasitic wasps that can also consume insects that are harmful to your garden. 

Yarrow can also provide other soil benefits to your lemon tree, outside of pest control. Yarrow’s deep root system can help aerate soil and provide excellent water infiltration, operating as a kind of living mulch. Yarrow can also serve the simple, yet important, function of reducing weeds around your lemon tree.

Growing and caring for yarrow plants involves providing ample growing room, sunlight, and pruning. Like lemon trees, yarrow plants prefer quite a bit of sun and don’t need a lot of water. With that said, yarrow does have a tendency to become invasive — which can make it difficult to control if its neglected for an extended period. For this reason, you may want to plant yarrow in its own pot or grow bed. You’ll need to give each plant at least one to two feet of space across and about a foot deep for its root system to spread efficiently. If planted in the ground, you’ll need to be vigilant to avoid having the plant take over your garden. You can curtail its spread by pulling up new sprouts and clipping flower heads to prevent the spread of seeds. 

If starting your yarrow plant from a seed, plant them in well-drained soil and grow it indoors in a well-lit area about six to eight weeks before the last frost in your area. Then, plant them outdoors after the risk of frost has passed. You can use the Old Farmer’s Almanac tool to determine the first and last frost dates for your zip code. Once the plants are mature enough, place them in pots or grow beds near your lemon tree, but avoid heavily shaded areas. Yarrow needs at least six hours of sun a day to thrive.