Celery is a rewarding vegetable to grow, but starting it from seed presents unique challenges. The tiny seeds are programmed to germinate only under specific, narrow environmental conditions, making the initial sowing phase temperamental. Understanding the precise number of seeds to sow and the required environmental factors is the first step toward a successful harvest of crisp, mature stalks.
Recommended Seed Density for Planting
Due to the small size and naturally lower viability of celery seeds, planting multiple seeds per location is standard practice to ensure at least one seedling emerges. For starting celery indoors in individual seed cells, the recommended density is typically three to five seeds per planting site. This approach acts as insurance against poor germination rates, which are common with this crop.
The physical act of sowing celery seeds is different from burying larger vegetable seeds. Celery seeds are light-dependent for germination and should be sown directly onto the surface of the pre-moistened growing medium. After scattering the cluster of seeds, gently press them into the soil surface to ensure good seed-to-soil contact without covering them. This shallow placement allows the necessary light exposure for sprouting to begin.
Specific Requirements for Successful Germination
Light and Moisture Requirements
Celery seeds are photoblastic, meaning light is a necessary trigger for them to break dormancy and sprout. If seeds are buried, the lack of light will prevent germination. This requirement makes maintaining consistent surface moisture challenging, as exposed seeds dry out rapidly. The seed coat must remain hydrated throughout the long germination period. To prevent drying, growers often cover the seed tray with a humidity dome or plastic wrap. Watering from the bottom of the tray also helps maintain soil saturation without disturbing the delicate, surface-sown seeds.
Temperature Stability
Temperature stability is a significant factor, as celery seeds prefer a narrow, relatively cool range for optimal sprouting. The ideal soil temperature for germination is between 68 and 75 degrees Fahrenheit. Temperatures that swing too high or too low can delay the process, which already takes 14 to 21 days, or prevent sprouting altogether. Maintaining this consistent warmth, often with a heat mat, is important when starting seeds indoors 10 to 12 weeks before the last expected frost date.
Thinning Seedlings and Final Plant Spacing
Thinning Seedlings
Planting multiple seeds makes thinning necessary once seedlings emerge. Thinning prevents competition for light, water, and nutrients, which would otherwise result in weak plants. The best time to thin is after seedlings develop their first set of true leaves. To remove excess seedlings, avoid pulling them out, as this risks disturbing the root system of the keeper plant. Instead, use small scissors to snip the weaker seedlings at the soil line, leaving only the healthiest plant in each cell.
Final Plant Spacing
Once seedlings are ready for transplanting, final spacing is important for proper development of mature celery stalks. Celery plants require significant space to produce thick, full stalks and are often planted in a block pattern to encourage self-blanching. The final distance between plants should be 6 to 12 inches apart in all directions. This spacing allows for adequate air circulation and ensures each plant receives the necessary resources to develop dense, crisp stalks.