▶What is the ideal greenhouse temperature and humidity for most plants?
Most vegetable seedlings and ornamentals prefer 60-70°F during the day and 55-65°F at night (cooler night temps slow growth but strengthen plants). Humidity should be 50-70%; too high (>80%) promotes mold and fungal disease, too low (<40%) stresses plants and increases spider mites. Use a thermostat with sensors (day/night setpoints), a ventilation fan with a humidistat to manage humidity, and a shade cloth in summer (prevents overheating). Crop-specific temperatures vary: lettuce and herbs prefer 55-65°F, tomatoes 65-75°F, tropicals 70-80°F. Check published crop guides or ask a consultant.
▶How do I propagate plants from cuttings and what is the success rate?
Cutting propagation: take 3-4 inch cuttings from vigorous growth, remove lower leaves, dip the cut end in rooting hormone (IBA powder, ~1000 ppm), insert into moist propagation mix (perlite, peat, coir), and maintain 70-75°F and high humidity (misting or a humidity dome). Root development takes 2-6 weeks depending on species. Success rates vary: easy (basil, mint, impatiens, begonias) 80-95%, moderate (woody ornamentals, herbs) 50-80%, hard (conifers, some shrubs) 20-40%. Hard-to-root species may need hormone dips, bottom heat, rooting jelly, or mist systems to succeed. Keep records: date, species, hormone concentration, success %; patterns guide future attempts.
▶What causes damping-off disease and how do I prevent it?
Damping-off is a fungal or oomycete infection that kills seedlings at the soil line (collapse), usually occurring in the first 2-4 weeks after germination. Causes: overly wet soil, poor air circulation, cold soil, or high humidity. Prevention: (1) Use sterile seed-starting mix (not garden soil), (2) Water carefully—moist but not waterlogged, (3) Ensure good airflow (oscillating fan at low speed), (4) Maintain soil temperature 65-75°F, (5) Avoid overhead watering (wet foliage promotes fungal spores). If damping-off appears, isolate affected trays, reduce watering, increase airflow, and apply a fungicide (sulfur or copper-based, approved for seedlings) per label. Prevention is much cheaper than recovery.
▶What is hardening off and when should I do it?
Hardening off is the gradual acclimation of greenhouse-grown seedlings to outdoor conditions (lower temperature, direct sun, wind, lower humidity) before transplanting into the field. Shock from sudden exposure kills or severely stunts plants. Process: 1-2 weeks before transplant date, move seedlings outdoors to a sheltered spot (shade, wind protection) for 1-2 hours, gradually increase exposure over 7-10 days (more hours, more sun, more wind). By the final days, plants sit in full sun for most of the day. Watch for wilting or bleaching (too much sun); adjust shade. Properly hardened seedlings are stocky, dark green, and ready for field stress.
▶How do I manage irrigation in a greenhouse without hand-watering every plant?
Drip irrigation (soaker tape or drip lines) and mist systems automate watering. Drip irrigation is ideal for potted plants and benches: water flows slowly directly to soil, no foliage wetting (reduces disease), and water/fertilizer loss is minimal. Install a timer and/or moisture sensor to control frequency (usually daily or every other day). Mist systems (overhead fine spray) are useful for propagation trays and humidity management. Soil moisture sensors alert you when watering is needed (avoid overwatering, the most common killer). Capillary mat systems wick water from a reservoir to pots (passive, low-tech, unreliable in hot weather). Most modern greenhouses use a combination: drip for crops, mist for propagation, sensors for monitoring.
▶How do I diagnose and treat common greenhouse pests?
Common pests: whitefly (small white flying insects on leaf undersides, sticky yellowing), spider mites (fine webbing, stippled leaves, mite appears as dust), aphids (curled leaves, sticky honeydew, clusters on new growth), thrips (silvery streaks on leaves, tiny yellow/black insects), and fungus gnats (small black flies in soil). Treatments: (1) Isolate affected plants, (2) Inspect closely (hand lens), (3) Spray with insecticidal soap, neem oil, or horticultural oil (approved for greenhouse/seedling use)—follow label rates and frequency, (4) Improve ventilation and reduce humidity to deter fungal diseases and mites, (5) Use beneficial insects (parasitoid wasps, predatory mites) for ongoing control. Prevent via sanitation (remove fallen leaves, disinfect benches), quarantine new stock, and scouting weekly.
▶What is the production cost and profit margin for a typical greenhouse crop?
Cost structure varies by crop. Vegetable seedlings (tomato, pepper, lettuce): seed ~$50/1000 seeds, potting soil ~$15/cubic yard, labor ~40 hours (wages), utilities (heat, electricity) ~$200-500/month, equipment depreciation. Retail price: $1-3 per cell-pack (6-pack of seedlings). Margin: if you spend $0.50 per 6-pack in inputs and labor and sell for $2, margin is 75% gross, but overhead (rent, management) reduces net. Finishing flowering plants: cost ~$2-3 per plant, sell $5-15. Specialty crops (microgreens, basil, lettuce for restaurants) have higher margins (cost $2-3, sell $8-15) but require exact climate and timing. Profitability depends on market proximity, crop selection, and efficiency. Talk to existing growers in your region for realistic numbers.