Top dressing with vermiculite significantly improves seedling growth.
Vijay Rapaka, Ph.D.
Research & Technical Support Manager
Smithers-Oasis Company, Kent, Ohio USA
Greenhouse Research Technician
Smithers-Oasis Company, Kent, Ohio, USA
In recent years, kale has become extremely popular due to its nutritional value and incredible health benefits. Kale is an excellent source of vitamins K, A, and C. Kale is also a very good source of vitamins B6, B2, and E, fiber, calcium, and potassium. Kale is a group of vegetable cultivars that belongs to Brassica oleracea. Kale belongs to Brasicaceae family, which includes several vegetables like cabbage, broccoli, cauliflower, collard greens, brussel sprouts, etc. Kale varieties can range from light green to dark purple and with different textures. Kale is easy to grow hydroponically and generally prefers cooler climatic conditions. Starting Kale in OASIS® Horticubes® XL* or Horticubes® ensures uniform germination and vigorous seedlings without any concerns of disease causing pathogens. The following are the salient features and benefits of in OASIS® Horticubes® XL or Horticubes® medium:
- The OASIS® foam growing media are a uniquely engineered propagation media
- They are thermoset foam materials and are considered to be sterile because of the high temperatures involvedduring the manufacturing process
- The OASIS® foam growing media are inert with no buffering capacity, as a result all the applied nutrients are readily available to the plants
- Horticubes® XL is a lower drainage and lower density medium, and Horticubes® is a relatively higher drainage and higher density medium. Both types of foam media are suitable for kale-seedling production. The lower density and finer cells of Horticubes® XL promote faster root penetration and also promotes profuse fine secondary roots which, in turn, promotes faster shoot growth
This Fact Sheet describes the general procedures for propagation and hydroponic production of kale. Further, it also demonstrates that top dressing with vermiculite significantly improves seedling growth.
The following is the general procedure for kale propagation using Kale in Horticubes® XL or Horticubes®:
- Seed: Make sure you are using a good quality seed with high germination percentage
- Media: Use Horticubes® XL or Horticubes® Medium (276 cell count) with multi-seed dibble hole *This product is available in limited areas.
- Tray: Choose the tray depending on the method of irrigation (solid bottom with drain holes for overhead irrigation and web-bottom tray for subirrigation)
- Initial Watering and Nutrition: This is the most important step for optimal success. The Horticubes® XL or Horticubes® sheets need to be thoroughly watered with Oasis® Hydroponic Fertilizer* (OHF 16-4-17) at
1 mS/cm (125 ppm N) or any other high-quality complete nutrient solution with first watering. The recommended procedure for proper initial watering is, float saturating the foam in complete nutrient solution followed by complete overhead flushing with a nutrient solution using a hose and a breaker. Refer to the Horticubes® or Horticubes® XL protocol sheet for a detailed step-by-step procedure.o Note:Floatsaturationshouldalwaysbefollowedbyoverflushingwithcompletenutrientsolution.
Not following the proper initial watering protocol can result in non-uniformity and delay in growtho Note:Usingcompletenutrientsolutionat1mS/cm(125ppmN)insteadofclearwaterwithinitialwatering will double kale seedling growth
- Seeding: After initial watering, place the seed in the dibble hole. With kale depending on the cultivar, it is recommended to place (~ 2 – 3 seeds / hole) and top-dress the seed with medium-grade vermiculite. Top dressing with vermiculite significantly promotes the seedling growth (see below)
- Germination: After seeding, the sheets can be placed directly in greenhouse under light or in a dark room for the first two days and then be moved to the greenhouse. The seeds germinate best at warm temperatures: 18°C to 24°C (65°F to 75°F). It takes about 2 to 3 days for the seeds to germinate
- Watering: On days 3 and 4, mist the seedlings once or twice per day depending on the greenhouse temperatures. From day 5 onwards, water once a day or every alternate day using a hose and a breaker if you are usingoverhead watering. Watering can be also done by subirrigating, using an ebb and flood systemo Note:Completenutrientsolutionat1mS/cm(125ppmN)shouldbeusedateverywateringeventduring the whole course of propagation.
- Light and Temperature: Kale seedlings can be exposed to full sunlight. Consider shading the greenhouse, when light levels exceed 500-600 μ.moles/m2/s. Maintain the average daily temperatures between 70° to 80° F
(20° F to 27° F).
- Transplant: Seedling will be ready to transplant within 10 to 15 days depending on the time of the year. The criteria for transplant is roots penetrating out of the bottom of the foam.o Note: Hold off watering the foam one day before transplant and this will allow easy separation of the foam cubes at transplant. *This product is available in limited areas.
The following is a research study with Red Russian Kale demonstrating that top dressing with vermiculite significantly improves seedling growth.
Materials and Methods
For this trial, the Horticubes® XL 276 count with multi-seed hole is float-saturated followed by complete overhead flushing with at 1 mS/cm of OHF 16-4-17 using a hose and a breaker. After initial watering, the seeds were seeded with 2 to 3 seeds / hole. The study had two treatments and three replications per treatment: In the case of Treatment 1, the seeds were covered with medium-grade vermiculite right after seeding and in the case of Treatment 2, the seeds were not covered with vermiculite and left exposed. The watering and the greenhouse climatic conditions were similar to the ones described above.
Photos were taken during the course of propagation and seedlings were harvested on day 14 and the data was subjected to statistical analysis.
When the seeds were covered with vermiculite, the germination was faster and consistent. As a result, the seedling started growing sooner. The seedling growth was 40% higher when covered with vermiculite compared to the ones that were not covered. The vermiculite covered seedlings were ready to be transplanted 3 to 4 days sooner compared to the non-covered seedlings.
Figure 1: Effect of vermiculite top dressing on Red Russian Kale. The seedlings were harvested 15 days after seeding and shoot fresh weight was measured.
Figure 2: Red Russian Kale, 5 days after seeding in Horticubes® XL. In the left tray, the seeds were covered with medium grade vermiculite and in the right tray the seeds were left exposed.
Figure 3: Red Russian Kale, 11 days after seeding in Horticubes® XL. In the left tray, the seeds were covered with medium grade vermiculite and in the right tray the seeds left exposed.
Figure 4: Red Russian Kale, 11 days after seeding in Horticubes® XL. The seedlings from vermiculite top dressed treatment (left) is ready for transplant, whereas the seedlings from no vermiculite treatment needs to be held for 4 more days to transplant (right).
The following is the general procedure for hydroponic production of kale:
Kale can be grown in a NFT (Nutrient Film Technique) system or in a floating raft system. Kale leaves can be harvested on a regular basis and the new leaves continue to grow. First harvest can be started 2 to 3 weeks after transplant into the main system.
Nutrition: Choosing balanced and right nutrient sources is the key to grow a high-quality and nutritionally-strong kale plant. The recommended EC for kale production is 1.25 mS/cm to 1.5 mS/cm.
• The following are the general mineral nutrient targets for kale – adapted from data collected at J.R. Peters Laboratory in Allentown, Pennsylvania.
o The recommended pH of the nutrient solution is 5.8 to 6.2
o For production, OASIS® Hydroponic Fertilizer* (OHF 16-4-17) or any other high quality complete nutrient solution can be used. Refer to the product technical sheet for detailed instructions on using OHF 16-4-17
- Temperature: Maintain the greenhouse day temperatures between 68° F to 80° F (21° C to 26° C) and night temperatures between 55° F to 70° F (12.5° C to 21° C).
- Humidity: Greenhouse relative humidity needs to be maintained between 40% and 60%. High humidity favors disease development and also nutrient deficiencies as transpiration is hindered.
- Light: Kale can be grown in full sunlight in the greenhouse. However, when light levels exceed
500 – 600 μ.moles/m2/s, consider shading the greenhouse. A 14 to 16h day length with 15 – 17 moles / day gives the best growth performance.
- Spacing: For optimal light utilization for maximum growth and proper humidity management, maintain a center-to-center spacing of 5″ to 6″.
Postharvest: Kale is marketed as fresh cut leaves or in bunches. The optimal conditions for maximizing the shelf life of kale is by storing between 32 – 36° F (0 – 2° C) and avoiding water loss. Kale is ethylene-sensitive, so store kale away from ethylene-producer produce such as apples, bananas, tomatoes, etc.
*This product is available in limited areas.