A fast, fine-leaved cover crop whose coiled lavender flower sprays feed bees and hoverflies for weeks, then cut down into soft green mulch.
Phacelia tanacetifolia · also called Lacy phacelia, Purple tansy
Windows are counted from the average date of your last spring frost.
Few plants pull in as many bees and aphid-eating hoverflies for as little effort. It also holds bare ground over a gap in the rotation and breaks down quickly once cut.
A little history. Native to the deserts and foothills of the southwestern United States and northern Mexico. Its flowers open in order along a coiled spray that uncurls as blooming moves outward.
Sow seeds ¼ inch (6 mm) deep, and aim for 4 inches (10 cm) between plants once thinned. Cover the seed ¼ inch and firm it in — light on the seed stalls sprouting. Keep the top half-inch moist until seedlings show. Seedlings emerge in 7–14 days.
Water every 2–3 days until seedlings are up, then only in dry spells. Water when the top inch of soil feels dry and seedlings look dull at midday. Aim for about 1 inch per week including rain while establishing.
None needed on ordinary garden soil. What to use: skip fertilizer — rich nitrogen makes soft stems that flop.
Shear the stand back by a third once the first flush of bloom fades to push a second, shorter round of flowers.
It's ready when cut when roughly a quarter of the stand is in flower and the coiled sprays are still unrolling — before any seed capsules turn brown. Shear stems at the soil line with hedge shears or a string trimmer. Leave the tops on the surface as mulch, or chop and turn them into the top 2 inches of soil.
Cut sprays hold several days in water as a cut flower. Keep leftover seed in a sealed jar somewhere cool and dark.
Sow a fresh patch every 3 weeks from early spring into early summer to keep flowers open for bees through the season.
Fall sowings often hold through mild winters and bloom early the next spring. Hard freezes kill the stand, which then lies flat as a protective mulch.
Oats
Sown into an oat cover, phacelia's open flowers feed hoverflies, lacewings and tiny parasitic wasps whose young hunt the aphids that build on cereal stands. The oats supply the bulk and root mass, phacelia the nectar the predators need.
Buckwheat
Both are quick, nectar-rich covers, but they release nectar at different times of day and hold bloom over slightly different weeks. Sown as a mix, they widen the daily and seasonal window that bees and hoverflies can feed in.
Apple
A strip of phacelia under or beside apples draws in hoverflies and parasitic wasps that often reduce aphid colonies on new shoots. Mow it in sections so beneficial insects always have flowers somewhere in the planting.
Bell Pepper
A short row of phacelia at the end of the pepper bed keeps hoverflies and ladybugs in the garden. Their larvae work through aphid colonies on pepper shoot tips, which often keeps numbers below the point of damage.
Broccoli
Cabbage aphids are the usual late problem on broccoli. Flowering phacelia nearby feeds the small parasitic wasps and hoverflies that hunt them, and the nectar keeps those insects on site instead of drifting off.
Zucchini
Squash needs bee visits to set fruit rather than shrivel at the tip. Phacelia flowering a few feet away raises overall bee traffic through the bed, which can help in gardens where pollinator numbers are thin.
Carrot
Phacelia is up and branching in two weeks while carrots are still hair-thin seedlings, and its lacy canopy shades them out. Keep it to the bed edge or a separate patch rather than sowing it through a carrot row.
Strawberry
Phacelia can hold a population of tarnished plant bug, and mowing the whole patch at once pushes those bugs into fruiting strawberries, where feeding causes misshapen berries. If you grow both, mow in strips and not while berries are sizing.
Easy-going — Phacelia can grow almost anywhere in the rotation without a strict rest.
The pea and bean family, the cabbage family or the tomato family thrive in this ground next season.
An easy-going crop that fits almost anywhere and gives back green bulk rather than taking. Leave 1 year before phacelia returns to the same ground. Follow it with peas or beans, a cabbage-family crop, or tomatoes and peppers, which all use the loosened, residue-fed soil well.
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