Asparagus

Plant crowns in spring, in a deep furrow you fill gradually

As soon as the soil is workable and no longer wet, dig a furrow 6 to 12 inches deep - shallower in clay (6 to 8 inches), deeper in very sandy soil (10 to 12 inches) - and lay one-year-old crowns head-to-toe, bud-up, so buds are 12 inches apart down the row. Space furrows at least 3 feet apart; 4 to 5 feet is typical where you have the room. Cover with only 2 to 3 inches of soil at first, then pull in more soil a few inches at a time as the ferns push up, until the furrow is level by the end of the season. A crown buried all at once in 10 inches of cold soil can exhaust its stored reserves before a shoot ever reaches light, but the same crown will climb out fine if you backfill in stages behind the growing ferns. The depth is what buys you a bed that keeps producing for fifteen years or more.

Water the fern, deeply and rarely

In the first two seasons after planting, give the bed 1 to 2 inches of water every other week. From the third year on, an established bed can go about 3 weeks between waterings, but water deeply enough to wet the soil 3 to 4 feet down. Keep it up all summer, long after harvest is over. A mature asparagus root system runs several feet deep, so light frequent sprinkling only wets the top few inches and trains roots shallow. The summer fern is the crop's factory, and a fern that wilts in August is a smaller harvest next April.

Pull mulch back from asparagusMar – Apr

Move heavy winter mulch off the row as spears begin, leaving aisles mulched for weed control. Cool wet mulch over crowns can delay spear emergence; aisles still benefit from weed-smothering mulch.

⚠ Watch for frost if soil warms early.

Feed the bed the moment you stop cutting

As soon as the last spear is cut and you let the row go to fern, apply a complete fertilizer such as 16-16-8 at about 1 pound per 100 square feet, and water it in. Do not feed heavily during the cutting window itself. Everything you harvest next spring is paid for by the sugars the ferns make this summer and send down to the crown. Fertilizing at the end of harvest lands the nitrogen exactly when the plant is building that fern canopy, not when it is only pushing stored spears.

Cut the ferns down once frost has browned them completely

Wait until frost has killed the ferns and they are fully brown, then cut them to short stubs at the soil surface and carry the debris out of the bed - do not leave it lying between the rows. If snow buries the ferns before you get to them, remove them first thing in spring, before the spears emerge. Cutting green ferns steals the reserves still moving down into the crown and cuts next spring's yield. But once they are brown they are only shelter: asparagus beetles overwinter in that dead stalk litter, and purple spot and rust spores ride it into spring.

Scout for asparagus beetle as the spears come up

From the day the first spears break ground, walk the row on warm sunny afternoons - between noon and 6 p.m., when the beetles are actually out and moving - and look for slate-blue adults, gray grubs, and the dark oval eggs standing on end along the spears. In a garden, act when about 10 percent of plants carry adults, 50 to 75 percent carry larvae, or 20 percent of spears carry eggs. Hand-picking into soapy water handles small beds. The overwintered adults emerge with the first spears and start laying immediately, and the eggs glued to a spear do not wash off - they go to the kitchen with the crop. Scouting in the morning badly undercounts them, because the beetles drop and hide when it is cool.

Asparagus beetle: carbaryl on spears only if scouting says so

If beetle counts pass threshold during cutting season and hand-picking is not keeping up, spray carbaryl on the spears at the low label rate, and do not reapply within 3 days. No more than 3 applications during the harvest season. Keep spraying to the spear stage - once cutting ends and the ferns go up, switch to cultural control and let the fern canopy alone. Adults feed on the spear tips and lay eggs on the stalks, and larvae hatching in about a week chew the fern later; knocking the first generation back during cutting is what keeps the summer population from building on the ferns.

⚠ Carbaryl carries a 1-day pre-harvest interval and a 12-hour re-entry interval on asparagus, a 3-day minimum retreatment interval, and a limit of 3 applications during harvest. Carbaryl is highly toxic to bees, and its label forbids applying it to crops or weeds in bloom - mow or avoid flowering weeds in the row first, and never spray asparagus ferns once they flower in summer, as the blooms are worked by bees. Follow the label on the product in hand; rates and intervals differ between carbaryl products.

Rust on the ferns: fungicide only after cutting ends

Once harvest is over and the ferns are up, watch for reddish-brown pustules that leave rust-colored dust on your fingers, worst after spells of warm days and cool dewy nights. If rust is established, myclobutanil can be sprayed on the ferns; wettable sulfur is another option. Cut and remove infected fern residue before spears emerge the following spring. Puccinia asparagi infects the fern, not the spear, and each summer pustule throws spores that reinfect the same canopy for months. A fern stripped by rust in August is a crown with nothing stored in it, and thin spears the next spring are the bill.

⚠ Myclobutanil carries a 180-day pre-harvest interval on asparagus, so it is a post-harvest fern spray only - it can never be applied during the cutting season. Sulfur has a 0-day interval.

Cut asparagus spearsApr – Jun

Harvest 6-8 inch spears during the harvest window, then stop and let ferns rebuild the crowns. Stopping harvest protects next year's yield by letting ferns recharge the root system.

⚠ Do not overharvest young beds.