Common Yarrow

• Fire-adapted, resprouting quickly from surviving rhizomes after a burn
• Yarrow’s strong scent doesn’t come from the volatile oils that make many aromatic shrubs burn hot and fast. Its foliage holds moisture, its sap is watery, and it doesn’t build up fine dead twigs
• Low, non-woody growth carries little fuel
• At a mature height of roughly 1 ft, with bloom stalks to 2 ft, it fits the height limits currently proposed for Zone 1

Yarrow’s flat, open clusters give access to short-tongued insects that can’t reach the nectar in deeper blooms. That structure draws a broad range of visitors, including bees and butterflies as well as the flies, beetles, and wasps most gardeners overlook. In a UC Davis study of forty-three California natives, yarrow drew more parasitic wasps than any other plant tested. It also drew high numbers of the herbivores those wasps hunt.

That’s the first lesson in trophic structure. The “pests” and the “beneficials” are part of the same food web, and yarrow feeds both sides of that relationship. Those parasitic wasps lay their eggs inside aphids and thrips, killing them as the larvae develop.

That predation feeds the Western Fence Lizards (Sceloporus occidentalis) that sun on fence rails and garden rocks throughout the Santa Cruz Mountains. They hunt the beetles, ants, and caterpillars that gather at yarrow’s blooms, turning insect abundance into a reptile a gardener can actually watch.

Take away the plants, and the insects go with them. Take away the insects, and so do the lizards.

That’s what trophic structure means. It’s not a list of who visits the plant. It’s a map of who would go hungry without it.

Insects need nectar and pollen for as long as they are flying. Most native perennials in the San Lorenzo Valley bloom fully for three or four weeks and then stop, which is a sensible strategy for the plant and a hard one for everything feeding on it.

Yarrow blooms from April into October. After opening alongside the spring natives, it keeps flowering through the gaps until Coyote Mint, California Aster, and California Fuchsia join the relay. It is rarely the showiest plant in bloom in any given week. It is simply there in all of them.

That continuity matters most in the dry months. A stand of Yarrow may be one of the few reliable nectar sources in a garden through midsummer. The insects it feeds in that stretch are prey for the birds, lizards, and wasps that hunt them throughout the season.

Pollinators

• The Xerces Society lists Common Yarrow as a plant of special value to native bees, and to the predatory and parasitoid insects that provide natural pest control in the garden
• Feeds small native bees, hoverflies, beetles, and wasps alongside the butterflies, all short-tongued visitors that can’t reach into deeper blooms

Butterflies and Moths

Common Yarrow is a larval host for the wavy-lined emerald moth (Synchlora aerata). This is not yet confirmed in the San Lorenzo Valley, but it is recorded on Achillea elsewhere in California. The caterpillar builds a shifting camouflage from bits of the yarrow it eats, attaching them to its own back spines

Predatory Insects

California hedgerow field studies found yarrow drew high numbers of Orius spp. (minute pirate bugs), predators of thrips and aphids

Overwintering Habitat

Left uncut over winter, the basal foliage and dried material shelter ground-dwelling insects

Yarrow weaves itself in among its neighbors, softening the edges between plants rather than holding a line.  That spreading comes from its rhizomes, so give it room to find its own shape instead of a fixed spot in a bed.

Let it weave, and the bare ground between your other plants becomes productive ground, in bloom and in habitat.

A dense, fibrous mat of roots spreads wide through the top layers of soil, gripping loose ground when planted on slopes, disturbed banks, or roadside cuts where rain would otherwise carry topsoil away.

Above ground, the fine, feathery foliage does its own version of this work. Left bare, rain hits soil directly, compacting it, crusting it over, and causing runoff. Yarrow’s finely divided leaves break the impact of each drop, slowing runoff so more water has time to soak in.

It’s a plant that holds the ground it grows in, for itself and for whatever’s planted near it next.

Web references (accessed August 2026):

• Calscape (California Native Plant Society)
• Fire Effects Information System (FEIS), USDA Forest Service
• Xerces Society

Published works:

• Bostock, S.J. 1978. Seed germination strategies of Achillea millefolium.
• Careddu, G. et al. — banana slug (Ariolimax) as a redwood-forest detritivore.
• Johnson, W. 1965. Western Fence Lizard diet study. Herpetologica.
• Long, R.F. & Anderson, J.H. 2013. Environmental Entomology 42(4).
• Lundin, O., Ward, K.L. & Williams, N.M. 2019. Journal of Applied Ecology 56:665–676.
• Barnard, R.L., Osborne, C.A. & Firestone, M.K. 2015. Soil microbial community response to wet-up under a Mediterranean-type climate. The ISME Journal/follow-on work.
• Snyder, B.A. et al. Litter consumption by the millipede Harpaphe haydeniana. Soil Biology and Biochemistry, 2013.