Rhubarb

Water deep and infrequently once established

For the first three years, irrigate once or twice a week so water penetrates 6 to 12 inches. From the third year on, cut back to once every one to two weeks but water deeply enough to wet 12 to 18 inches of soil. The crown roots deeply once established and pulls moisture from well below the surface, so frequent shallow watering keeps the crown wet without ever reaching the roots that matter.

⚠ Do not overwater. Root and crown rot in rhubarb is a consequence of saturated soil, and there is no fungicide that will save a rotted crown.

Three inches of straw over the root zone

Once the soil has warmed and growth is underway, lay 3 to 4 inches of straw or compost around the crowns, keeping the material pulled back from the buds themselves. Rhubarb is a shallow-rooted perennial that cannot be cultivated close in without cutting feeder roots, so mulch is the only practical way to hold weeds off the crown and steady the soil moisture.

Feed nitrogen just before the leaves push

Just before the buds break in spring, scatter about half a cup of 16-16-16 granular fertilizer around the base of each established crown and work it lightly into the soil. Do not apply fertilizer during the establishment year. Rhubarb rebuilds its whole crown from stored reserves in a few weeks of spring growth, and the stalks you pull are that growth, so nitrogen has to be in place before the leaves expand rather than after.

⚠ Do not fertilize during the first establishment year, and keep granules off the crown itself where they can burn the emerging buds. Have soil tested before adding phosphorus; on soils already high in phosphorus a complete blend may not be appropriate.

Divide crowded rhubarbMar – Apr

In early spring, lift old crowded crowns and replant divisions with at least one bud and a strong root piece. Older crowded crowns produce smaller stalks; division renews vigor every few years.

⚠ Keep divisions moist and replant promptly.

Cut the seed stalk the day you see it rising

As soon as a thick flower stalk begins to elongate out of the center of the crown, cut it off at the base. Check the plant weekly through the bolting period, because a crown will often send up more than one. Setting seed spends the crown's carbohydrate reserves on flowers instead of leafstalks, and a plant allowed to bloom drops its stalk yield for the rest of the season and into the next.

Strip and destroy the leaves after the first hard frost

Once a hard frost has killed the tops, remove every leaf and all the dead litter from around the crowns and destroy it. Do not compost this material back onto the bed. Ascochyta and Ramularia leaf spot overwinter in that dead tissue and release the spores that infect next spring's new leaves, so clearing it is the whole control program for both diseases.

⚠ Rhubarb leaves are toxic and must never be eaten. Keep the removed foliage away from livestock and out of the kitchen.

Rhubarb curculio: pull the dock, pick the beetles

Look over the leafstalks and crown for a rusty, snouted beetle about three quarters of an inch long, and for oozing holes bored into the stalks. Handpick any beetles you find, and grub out curly dock and wild dock growing anywhere near the patch. The curculio cannot complete its life cycle on rhubarb alone. It breeds in dock, then moves into rhubarb to feed and bore, so removing the alternate host is what actually breaks the cycle.

Straw over the crowns once the ground freezes

After the ground has frozen and the tops are gone, cover the crowns with 2 to 3 inches of straw for the winter. Waiting for the ground to freeze is the point: the mulch is there to keep the soil frozen through midwinter thaws, because it is the freeze and thaw cycling that heaves shallow rhubarb crowns out of the ground.

Pull rhubarb stalksApr – Jun

Harvest stalks by twisting and pulling from established plants, leaving enough leaves to rebuild the crown. Rhubarb needs foliage after the harvest window to store energy for next spring.

⚠ Never eat rhubarb leaves.