- Hand remove all weeds prior to seeding.
- Remove any debris that may house insects.
- Do not apply herbicide in greenhouse!
- Thoroughly remove all soilless media and plant debris.
- Steam at 176°F for 30 minutes.
- Thoroughly rinse with 50% household bleach solution prior to each clipping and when transitioning between greenhouses.
Source Water Solution Analysis
- Analyze water to monitor pH, bicarbonates, and trace elements. Sample with a well-rinsed 16-oz drink bottle. Run water several minutes before sampling. Sampling can indicate when to reduce excessive bicarbonate concentration (Figure 1).
- Optimum daytime: 86°F
- Optimum nighttime: 68°F
- Fluctuate temperatures to break seed dormancy.
- Reduce nighttime temperature to 55°-60°F after stand establishment (14-20 days after seeding).
- Seed trays when five-day forecast predicts bright, sunny days.
- Cold-injured seedlings (Figure 2) will recover with addition of warm air.
- Use 2-1-2 or 3-1-3 ratio fertilizers (for example, 20-10-20 and 16-5-16).
Phosphorus (P) and Potassium (K)
- 2-1-2 or 3-1-3 ratio fertilizers provide sufficient P and K when targeted N rate is achieved.
- Excessive P can cause leggy or spindly transplants.
- P deficiency (Figure 4) is rare when recommended fertilizers are used.
- Sufficient Ca should be included in commercial media; if not, add 5 oz gypsum/100 gal of float water prior to seeding.
- For deficiency (Figure 5), apply 3.51 oz of calcium nitrate/100 gal of water overhead or to float water. Either will provide 50 ppm Ca and 40 ppm N.
Magnesium (Mg) and Sulfur (S)
- Use standard fertilizers to supply sufficient Mg and S. For deficiency, add Epsom salts at a rate of 4 oz/100 gal of float water.
- Use fertilizer with 0.02% B to ensure trace amount of B. Float bed concentration should be 1-2 ppm; less than 0.5 ppm is considered low. To correct, add no more than 0.2 oz Borax/100 gal of float water (this will supply 1.5 ppm B). Collect a water sample prior to seeding to determine B levels. Remember B is toxic to plants when concentration exceeds 2 ppm (Figure 6)! Add total source water B content to fertilizer B to determine total B concentration in float bed. Collect a diagnostic float water sample after fertilizer addition to analyze B concentration.
Calculation for Gallons of Water in a Float Bed
- Length (ft) × width (ft) × depth (ft) × 7.48 gal/cubic foot = gal of water/bed.
- Desired ppm of nutrient ÷ (% concentration in fertilizer × 0.75) = oz of fertilizer/100 gal.
- Sanitize and ventilate to control disease.
- Dispose of old and diseased trays. Steam-sanitize trays (176°F for 30 min) between each use to prevent Pythium root rot and Rhizoctonia diseases.
- Pythium Root Rot: Terramaster 4EC
- Preventative rate = 1.0 fl. oz/100 gal of float water.
- Curative rate = 1.4 fl. oz/100 gal of float water.
- Mix Terramaster well throughout float bed. Root pruning is expected. Apply 3-8 weeks after seeding. Maximum use of Terramaster is 3.8 fl. oz/season.
- Target Spot (Figure 7): Quadris F
- 0.14 fl. oz/1,000 square feet. Use at least 5 gal of water/1,000 square feet. Coverage is critical! Apply only once prior to transplanting.
- Black Root Rot/Tobacco Mosaic Virus/Collar Rot (Figure 8 and Figure 9):
- No chemical control exists; discard infected trays and seedlings.
Seedling Growth Management
- Clip properly to ensure plant uniformity, hardiness, and maximum usable seedlings.
- Clip when plants are 2-2.5 inches above tray or 1.5 inches above bud.
- Clipping 5 times improves viability by increasing stem diameter and reducing stem elongation. After fifth clipping, seedlings are only being “held” until transplanting.
- Discard plant clippings at least 100 yards from greenhouse for sanitation.
For aphid, flea beetle, or caterpillar management in greenhouse:
- Orthene = 0.375 oz in 3 gal of water/1,000 square feet during seedling production.
- Bt materials are another caterpillar control option.
For aphid, flea beetle, or thrips management in greenhouse within 5 days of transplanting or for field protection:
- Imidacloprid (Admire Pro and others) = 0.6-0.8 fl. oz/1,000 plants (check formulation) for field protection.
- Thiamethoxam (Platinum SC and others) = 0.8 fl. oz/1,000 plants (check formulation) for field protection.
- Apply Admire Pro and Platinum overtop of transplants and rinse immediately to ensure media wash-in.
- These materials can also provide control of soil insects such as wireworms at higher rates. Refer to the North Carolina Agricultural Chemicals Manual for soil insect control recommendations.
Estimated EC Meter Reading Examples
100 ppm N
150 ppm N
* Correcting bicarbonates with acid will elevate EC reading.
Publication date: Feb. 26, 2020
Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your local N.C. Cooperative Extension county center.
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