What To Plant In A South Carolina Greenhouse For Herbs And Salad Greens

South Carolina offers a long growing season but also extremes of heat, humidity, and occasional cold snaps depending on inland or coastal location. A greenhouse gives you control over microclimate so you can grow fresh salad greens and aromatic herbs year round. This guide explains which varieties perform best in South Carolina greenhouses, practical planting schedules, environmental control, soil and container choices, and pest and disease prevention. Concrete tips and planting details make this actionable whether you are a hobby grower or producing for a small market.

Understanding South Carolina greenhouse conditions

South Carolina spans USDA zones roughly 6a to 9a. Coastal areas are milder in winter and hotter and more humid in summer; upstate has cooler winters and sometimes late spring frosts. In a greenhouse you need to manage:

• temperature swings: high summer heat and potential winter lows;
• high humidity that encourages fungal disease;
• light intensity that can be too strong in summer and too weak in winter.

Control is achieved with ventilation, shade, heating, fans, and supplemental light. For herbs and salad greens, aim for daytime temperatures of 60 to 75 F (15 to 24 C) most of the year, and nighttime temps no lower than 45 to 50 F (7 to 10 C) for tender herbs.

Which herbs to prioritize in a South Carolina greenhouse

Herbs that handle warmth, humidity, and container culture will be your best performers. Prioritize these for reliable production and flavor.

• Basil (Genovese, Sweet, Thai)
• Parsley (Italian/flat-leaf and curly)
• Cilantro (Coriander)
• Chives and garlic chives
• Thyme
• Oregano
• Rosemary
• Sage
• Dill
• Lemon balm
• Tarragon (French)

Each herb has specific needs; below are practical planting details.

Basil

Basil thrives in warmth and light. It is one of the quickest and most profitable greenhouse herbs.

• Seed depth: 1/8 to 1/4 inch.
• Ideal temps: 70 to 80 F day, not below 55 F night.
• Spacing: 8 to 12 inches for cut-and-come-again; 16 inches for full heads.
• Days to harvest: first cut at 3 to 4 weeks; mature heads in 6 to 8 weeks.
• Notes: pinch flowers to prolong leaf production. In high humidity, ensure good airflow to avoid fungal leaf spots.

Parsley

Parsley prefers slightly cooler conditions than basil and tolerates partial shade.

• Seed depth: 1/4 inch.
• Ideal temps: 60 to 70 F day.
• Spacing: 6 to 8 inches.
• Days to harvest: 6 to 8 weeks for baby leaves, 10 to 12 weeks for full clumps.
• Notes: seed germination is slow; soak seeds overnight and use vermiculite cover to speed up.

Cilantro

Cilantro prefers cool weather and bolts rapidly in heat, so greenhouse cooling and succession sowing are essential.

• Seed depth: 1/4 inch.
• Ideal temps: 50 to 70 F.
• Spacing: 4 to 6 inches for leaf harvest; 12 inches if letting go to seed.
• Days to leaf harvest: 3 to 4 weeks for baby leaves; full flavor in 6 to 8 weeks.
• Notes: grow in cooler season or in shaded, ventilated summer benches.

Rosemary, Thyme, Oregano, Sage

These Mediterranean herbs prefer drier soil and good light. Grow them in coarser, well-draining mixes and avoid overwatering.

• Soil: gritty, pH 6.0 to 7.0.
• Water: allow surface to dry between waterings.
• Harvest: trim continuously to encourage bushy growth.

Salad greens that do well in a South Carolina greenhouse

Salad greens are the backbone of a greenhouse kitchen garden. Choose fast-growing, heat-tolerant varieties for summer and cool-season varieties for winter.

• Lettuce (looseleaf, butterhead, romaine)
• Arugula
• Spinach (including baby spinach)
• Mache (corn salad) for cool months
• Mizuna, tatsoi, and other Asian greens
• Mustard greens
• Baby kale and chard
• Bok choy and pak choi
• Endive and escarole
• Microgreens (broccoli, radish, sunflowers, mustard)

Lettuce

Lettuce is easy to grow, but heat tolerance varies by type.

• Best types for summer: looseleaf varieties and heat-tolerant mixes; avoid delicate butterheads in extreme heat.
• Seed depth: 1/8 inch.
• Spacing: 4 to 8 inches for baby leaf; 8 to 12 inches for full heads.
• Days to harvest: 25 to 45 days depending on type and whether harvesting baby or mature heads.
• Notes: use shade cloth (30 to 50 percent) during peak summer to prevent bolting and bitterness.

Arugula and Mustard

Fast-growing and flavorful, arugula and mustard tolerate cooler and mild heat.

• Seed depth: 1/8 to 1/4 inch.
• Spacing: 2 to 6 inches for baby leaf; 8 to 12 inches for mature plants.
• Days to harvest: 20 to 30 days for baby leaves.
• Notes: succession sow every 7 to 10 days for continuous harvest.

Spinach and Mache

Spinach prefers cool conditions. In winter a greenhouse will easily provide suitable temps if you insulate or heat slightly at night.

• Seed depth: 1/4 inch.
• Ideal temps: 45 to 65 F.
• Days to harvest: 30 to 45 days.
• Notes: consider New Zealand or Malabar spinach for hot months; they are heat-tolerant climbing greens.

Planting schedules and succession planning

Greenhouses allow year-round production if you match varieties to seasons and use succession sowing.

• Winter: focus on hardy greens (lettuce, spinach, mache, tatsoi, kale) and hardy herbs (parsley, thyme, rosemary). Heat if overnight temps fall below 40 F.
• Spring: sow basil after last significant cold and begin continuous sowing of salad greens.
• Summer: shade and ventilate. Grow heat-tolerant greens and focus on basil, oregano, rosemary; consider hydroponic systems and evaporative cooling.
• Fall: replant cool-season greens for high-quality flavor; harvest herbs for preservation.

Practical schedule: sow salad green trays every 7 to 14 days for continuous baby-leaf harvest. For herbs like basil, sow every 3 to 4 weeks for staggered production.

Soil, containers, and substrate recommendations

Good substrate is essential for consistent yields.

• Use a sterile, well-draining mix for containers and raised beds: equal parts peat or coconut coir, composted pine bark, and perlite or vermiculite.
• pH: target 6.0 to 6.8 for greens and most herbs. Adjust with lime or sulfur as needed.
• Fertility: a balanced organic fertilizer or controlled-release formula (e.g., 14-14-14) is fine. For salad greens, keep nitrogen available for leafy growth.
• Container sizes: 6-inch pots for individual herbs; 8 to 12-inch pots for larger basil and parsley; 4 by 20 inch troughs or 10 by 20 inch flats for salad greens.
• Hydroponics: NFT, deep water culture, or ebb-and-flow are excellent for greens and herbs and reduce disease from soil pathogens.

Watering, irrigation, and humidity control

Consistent moisture without waterlogging is the goal.

• Irrigation: drip lines, micro-sprayers, or ebb-and-flow systems work well. Hand-watering with a gentle wand is fine for small setups.
• Watering frequency: daily during hot weather, every 2 to 4 days in mild conditions. Always check substrate moisture.
• Humidity: maintain 50 to 70 percent relative humidity for greens; lower humidity in warm months reduces fungal risk. Use ventilation and dehumidification if necessary.
• Airflow: place oscillating fans to promote leaf drying and reduce pest and disease pressure.

Light and temperature management

Light and temperature drive flavor and growth.

• Light: most herbs and greens need 10 to 16 hours of light. In winter, add full-spectrum LED fixtures to supplement short days.
• Shade cloth: use 30 to 50 percent shade in high summer, depending on greenhouse orientation and thermal buildup.
• Heating: small propane or electric heaters may be needed for winter nights if temps drop below recommended range. Use thermostats and safety devices.
• Ventilation: automatic vents and exhaust fans are essential for summer cooling and humidity control.

Pest and disease management

Greenhouses are not pest-free. Integrated pest management (IPM) is the most sustainable approach.

• Common pests: aphids, whiteflies, thrips, fungus gnats, slugs, and spider mites.
• Diseases: damping off, botrytis (gray mold), downy mildew, and various leaf spots.
• IPM steps:
• Monitor daily and inspect undersides of leaves.
• Use sticky traps for flying pests.
• Encourage beneficials: predatory mites, lacewings, and parasitoid wasps.
• Use biological controls (Bacillus thuringiensis for caterpillars, Beauveria for certain pests).
• Remove infected plants promptly and sanitize tools.
• Avoid overhead watering to cut down on fungal disease.
• Sanitation: sterilize seed trays, rotate crops, and steam-sterilize soil mixes if reusing.

Harvesting, postharvest handling, and preservation

Timing and technique affect flavor and shelf life.

• Cut-and-come-again: harvest outer leaves of lettuce, kale, and herbs to promote regrowth. For lettuce, never cut below the crown.
• Whole-head harvest: for romaine and butterhead when heads are firm.
• Harvest time: pick in the morning after dew has dried but before heat spikes to preserve flavor and turgor.
• Postharvest cooling: place harvested greens in cool water briefly, then spin or gently blot dry and store at 32 to 36 F with high humidity (90 to 95 percent).
• Preservation: dry or freeze excess herbs. Basil preserves poorly when frozen unblanched; make pesto and freeze in small portions.

Practical supplies checklist

• Thermostat-controlled heater and ventilation fans.
• Shade cloth (30 to 50 percent).
• Oscillating fans for airflow.
• Sterile potting mix and perlite.
• Drip irrigation or ebb-and-flow set-up.
• Seeds of recommended varieties and sticky traps.
• pH meter and basic soil test kit.
• LED grow lights for winter production.

Quick troubleshooting and takeaways

• If plants are bolting early: reduce temperature, increase shade, and choose heat-tolerant varieties.
• If leaves are yellow with normal moisture: check pH and nutrient levels; consider a balanced feed.
• If you see fungal spots: improve airflow, reduce humidity, and remove affected tissue.
• Succession sowing every 7 to 14 days keeps a steady supply of baby greens.
• Match herb choice to microclimate: Mediterranean herbs in drier pots, cilantro and parsley in cooler benches.

A South Carolina greenhouse can deliver exceptional herbs and salad greens year round when you match crop selection to seasons, control temperature and humidity, use good substrates and irrigation, and adopt IPM practices. Start with the recommended varieties, plan your sowing schedule, and optimize light, ventilation, and water. With these details in place you will have consistent harvests, better flavor, and reduced disease pressure.