Rhubarb Care At A Glance
- Rhubarb crowns should be planted in early spring, usually 2 to 4 weeks prior to last average the frost date. Cool-weather aids establishment.
- Plant in well-drained, organically rich soil in full sun.
- Plant shallow, with the top of the tuber only 1-2 inches below natural grade.
- Do not harvest the first year. Allow plants to grow & mature well first.
Rhubarb Planting Instructions (from bare root)
Rhubarb crowns/tubers are simply a section of divided mature roots. They are live crowns of viable tissue, but they are dormant when shipped. It is common for some surface mold to grow on rhubarb crowns. If it is present or develops, simply wipe it off with a moist rag and drop or two of dish soap, then allow crowns to air dry. This type of surface mold does not affect the long-term performance or health of the rhubarb plants. Once in the ground, the mold dies.
- Dig and prepare a planting hole 10-12 inches deep and 1-2 ft. wide, blending ample amounts of either compost or aged manure into the natural soil. 1 cup of bone meal or ½ cup of superphosphate can also be added to this backfill at the bottom of the hole.
- Good drainage is essential, as dormant rhubarb crowns are susceptible to rotting before they start to grow. Backfill the hole and firm amended soil well enough to avoid any settling. Once the soil is firm, set tubers with the crown or growing tip no more than 1-2 inches below the soil surface.
- If you are setting multiple plants, space them at least 3 to 4 ft. apart. Ensure all competitive weeds, especially perennial weed grasses like Quackgrass are removed in 3 to 4 ft. diameter around newly planted rhubarb crowns. Cover the bare ground with 2 to 3 inches of compost or mulch, making sure to not cover the rhubarb crown any deeper.
- After crowns are planted, water thoroughly to settle the soil and eliminate any air pockets.
- Do not over-water new rhubarb crowns. Dormant crowns are sensitive to overly wet soils before they start to grow out. Apply water modestly until new shoots become visible. Once new leaves are produced plant will require more water. Utilize the 1 in. of water per plant, per week rule when new leaves appear.
Rhubarb Care - Maintenance After Establishment
- Rhubarb are heavy feeders. Fertilizer should be applied annually to the plants in early spring. Use a liberal application of rotted manure or about 1/2 pound (1 cup) of a complete fertilizer such as 5-10-20 or 10-10-10 per plant. Organic fertilizers like 3-5-3 and Dave Thompson's Healthy Grow are other good options for rhubarb plants.
- After plants are established, supplemental watering becomes most important during summer during periods of heat and drought. Rhubarb soil should be kept evenly moist but not soggy. Applications of mulch or compost as top-dressing in spring and again in mid-summer can help keep roots cool and from drying out too much.
- Divide large plants in early spring by cutting down through the center of the plant with a sharp spade, leaving 50% of the plant intact. Once removed, dust the cut surface with a fungicide such as Captan® WP or sulfur powder to help prevent fungal disease and bacterial infection.
- The removed portion can be divided in ½ again, but dust those cut surfaces with fungicide powder and allow them to sit out for 2 to 3 days to callous the cut surface. Follow proper soil prep & planting instructions as outlined above. Do not harvest stalks from the transplant until the following year.
Rhubarb Special Needs & Troubleshooting
Issue: Newly panted crowns not leafing out or growing.
Causes: Could be too soon. Crowns may have been planted too deep. Or wet soil can cause crowns to rot.
Solutions: New crowns can take 6-8 weeks to form roots enough to form new leaves. If weather conditions are unseasonably cool, plants will wait to leaf out to avoid the risk of frost. Be patient. Avoid overwatering dormant crowns. To prevent crown rot, ensure the planting location has excellent drainage.
Issue: Rhubarb plants produce flower stalks. Rhubarbs are perennial plants that sometimes produce flower stalks.
Causes: This is referred to as "bolting", as with other vegetable plants that go to flower in order to produce seeds. Bolting can happen for several reasons, including mature plants that need to be divided, general plant stress from late frosts, fluctuations in temperatures, excessive heat, drought, disease, insect pressure, or nutritional imbalances.
Solutions: Remove flower stalks as soon as they are discovered. Blooms are undesirable, as they sap the strength of the plant and prevent future harvestable leaves. Follow proper fertilizing, watering, and top-dressing to keep plants as healthy as possible during the growing season. Mature rhubarb plants should be divided once every 3 to 5 years in early spring, making sure to leave 2-3 growth eyes per section for good re-growth.
Issue: Yellow leaves in spring.
Causes: Crown rot or soil-borne wilt diseases can cause yellow-wilting spring foliage.
Solution: Prevent soggy, saturated soils by planting in well-drained organically healthy soil.
Issue: Plants only form thin or spindly stems and leaves.
Causes: Plants may be too mature, or nutritionally deprived.
Solution: Rhubarb plants should be divided once every 3-5 years to keep plants producing. Rhubarbs are healthy feeders, follow fertilizing instructions found above.