Greenhouse Transplant Production Tips
Soon many vegetable growers will be rolling up their sleeves to start transplants for the coming season. Transplants that are healthy,
robust, and free of pests and diseases have a prolonged effect on crop growth and performance.
Vegetable transplants provide a head-start to target early season market, and ensure a good stand of vegetable plants without the uncertainty of direct seeding or the added cost of field thinning. However, production of transplants calls for early planning and optimum utilization of available resources. This is critical especially for vegetables like tomato, pepper, and celery that need sufficient growing time to attain adequate size. Growers must pay attention to the 10 areas below in order to ensure a healthy crop.
STEP 1. Greenhouse Sanitation
Transplant production greenhouses should be free of plant debris, accumulated soils, and weeds that may harbor insect pests and diseases. Benches and floors should be properly disinfected prior to use. Products such as chlorine bleach, Green-Shield, Physan 20, Oxidate (hydrogen dioxide, BioSafe Systems), chlorine dioxide, etc. can be used to clean and sterilize greenhouse benches.
Product labels need to be followed precisely depending on purpose and mode of use. Disinfecting benches and floors is an effective method to limit diseases such as Pythium and Rhizoctonia. Sanitation is also applicable to personnel entering and handling plants in the greenhouse.
STEP 2. Ventilation And Heating
Greenhouses should ensure proper ventilation, air flow, and heating for healthy plant growth. Good ventilation and air circulation is important as it helps keep the foliage dry and mitigates various bacterial and fungal diseases. Well aerated and ventilated greenhouses can maintain low relative humidity, thereby eliminating common diseases such as botrytis gray mold and late blight.
Uniform and optimum temperatures are essential for plant development and production of uniformly sized transplants. Thermometers should be placed at plant level in several locations to monitor air temperature. Temperature control is critical and should be tailored based on specific crop requirements.
STEP 3. Transplant Trays
Multi-cell plastic trays are widely used and are available in many cell sizes and numbers. Tray selection depends on plant species, duration of transplant growth, and available greenhouse space. Larger cell sizes can be used for transplants that need longer growth cycle (more than five weeks) and have larger root system, like asparagus. Larger cell sizes have the advantage of holding more media, thus moisture and nutrients, but compromise on greenhouse space. For smaller cycle crops, such as leafy greens, a smaller cell is appropriate as the root growth seldom fills the cell space.
Most growers reuse transplant trays and containers for economic and environmental reasons. Trays and containers should be sanitized with sanitizing solutions after each use to prevent the spread of diseases.
STEP 4. Seed Quality
Seed quality is critical for successful transplant and crop production. High-quality seed has higher germination percentages compared to old seeds that often have poor germination, leading to losses in uniformity, revenue, and productivity. If using old seed, it is important to perform germination tests preferably one month before the actual start date of transplant production.
STEP 5. Growing Media
Vegetable growers have the option of using soil mixes or artificial mixes when producing vegetable transplants. The best growing medium is the one which has good moisture-holding capacity, good drainage, and high nutrient retention capability. There is a huge selection of soil-less commercial media available. These soil-less mixes are sterile, easier to handle, and carry a small quantity of start-up fertilizers for initial seedling growth.
For soil mixes, make sure the soil is sterilized, light, well drained, and free of chemical residues. A soil test could be useful to correct for pH, salt, and fertility issues.
STEP 6. Irrigation Management
The success of transplant production can be stymied by improper irrigation management. Some things to consider while making irrigation decisions are when, how, and how much to water. In early stages of seed germination it is critical that the media is kept moist at all times. As the seedlings grow roots and get established, water the plants only when moisture is needed.
Water should be evenly distributed across the flats and uniformly applied without missing corners of flats and benches. Over watering often promotes growth of fungus gnats and certain diseases especially damping-off.
STEP 7. Nutrient Management
Fertigation, or the use of water-soluble fertilizers at the time of watering, is a common method of fertilizing vegetable transplants. No generalized fertilization regimen is available, but a common alternative includes a 75 to 100 ppm nitrogen (N) solution applied twice weekly, or a 300 to 500 ppm N solution applied once a week. If higher concentrations of fertilizer are used periodically, it is recommended to occasionally flush the root zone in order to mitigate issues related to salt accumulation. Adjust fertilization according to temperature and light conditions. Tall and leggy transplants are produced as a result of low light conditions coupled with high fertilizer rates, and/or over watering.
STEP 8. Lighting
In the northern climate zones, short day lengths and lack of sufficient quantity of light during spring season can adversely affect transplant production and limit plant growth. High-pressure sodium lamps (400 watt) are commonly used for supplemental lighting in greenhouses; however, escalating energy costs make their use cost-prohibitive.
STEP 9. Pest And Diseases
The best control for pests and diseases is proper greenhouse sanitation, proper formulation of the growing medium, proper irrigation scheduling, proper fertilization practices, and constant monitoring and removal of infested or infected plants. A number of disease problems can be minimized by keeping the water off the foliage. Under severe outbreak of pest and diseases, selective pesticides should be used according to labeled rates and timing.
STEP 10. Hardening Off
The process of hardening off is achieved by removing the optimum growing conditions of the greenhouse. This can be done by reducing the amount of water and/or fertilizer and reducing greenhouse temperature by 5°F to 10°F. Alternatively, transplants can also be hardened by moving them out of the greenhouse and placing them in a lath house for a week or two before transplanting. Hardened plants can rapidly recover from transplant shock and better withstand adverse field conditions such as low temperatures and high winds.
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