Rhubarb is a perennial vegetable cultivated for its tart, edible stalks, making it a favorite for early spring harvesting. While planting pre-grown crowns is the most common method, starting rhubarb from seed offers a cost-effective alternative for establishing a large patch. Successfully growing rhubarb from seed requires careful timing and patience to establish a strong root system. Understanding the multi-year timeline and following specific indoor preparation steps will lead to a productive, long-lasting rhubarb patch.
Optimal Timing for Starting Rhubarb Seeds
The most effective strategy for starting rhubarb seeds is to sow them indoors during the late winter months. This indoor start should typically occur between eight and ten weeks before the average last spring frost date. The seeds germinate best in a temperature range of 60 to 75°F. Providing bottom heat with a seedling heat mat helps maintain this soil temperature, encouraging the seeds to sprout within two to three weeks. Once the last danger of frost has passed and the seedlings are established, they can be safely moved to a permanent outdoor location.
For direct outdoor sowing, the timing must align with soil temperatures around 60 to 70°F. This usually corresponds to early spring, about two weeks before the final expected frost, or in late autumn in regions with milder winters. Fall planting involves natural stratification, where cold, moist soil breaks the seed’s dormancy, allowing for germination the following spring.
Step-by-Step Sowing Procedure
Before planting, soak the seeds in warm water for a few hours; this softens the seed coat and accelerates the sprouting process. Use a quality, sterile seed-starting mix in small trays or two to three-inch pots to prevent disease and provide a light, well-draining medium. Plant the seeds at a shallow depth, covering them with approximately one-quarter to one-half inch of the mix. Planting two seeds per cell and later thinning out the weaker seedling ensures a higher chance of success.
After sowing, the containers must be kept consistently moist but never waterlogged, as excessive moisture can lead to fungal issues like damping off. Maintaining the temperature range of 60 to 75°F is important during germination. Placing the containers in a bright location that receives plenty of indirect light, or under grow lights, will ensure the young seedlings develop stocky, healthy growth.
Hardening Off and Transplanting Seedlings
Before transplanting, seedlings must undergo a gradual transition known as hardening off. This process conditions the tender plants to tolerate the harsher outdoor elements, such as direct sunlight, wind, and cooler temperatures, preventing transplant shock. The hardening off period should last between seven and ten days. Begin by placing the potted seedlings in a sheltered, shady outdoor location for just a few hours a day, progressively increasing the duration of their outdoor exposure over the course of the week.
Once the threat of spring frost has passed and the seedlings have developed two sets of true leaves and reached about four inches, they are ready for the garden. Prepare the permanent planting site by tilling the soil to a depth of at least two feet and amending it heavily with aged compost or manure, as rhubarb is a heavy feeder. Plant the seedlings at the same depth they were growing in their containers, ensuring a generous spacing of at least three feet between plants to accommodate their mature size.
The Long Wait: Harvest Timeline from Seed
Growing rhubarb from seed requires patience, as the plant dedicates its first few seasons to establishing a robust root system. During the entire first growing season after transplanting, the plant should be left completely undisturbed. Allowing the plant to focus all its energy on root development ensures its long-term health.
In the second year, the plant will be more mature, and a minimal harvest can be taken, consisting of only a few stalks. The first full, reliable harvest typically occurs in the third season after the seed was initially sown. The mature crown can then support the removal of up to a third of its stalks without compromising its health. This multi-year timeline contrasts with planting crowns, which often allow for a light harvest in the second year, but the wait ensures a long, productive life for the seed-started plant.