What To Plant in a Colorado Greenhouse for Year-Round Harvest

Growing year-round in Colorado demands planning, plant selection, and greenhouse management that responds to wide temperature swings, high elevation sunlight, and dry air. A properly equipped and managed greenhouse transforms short outdoor seasons into continuous harvests. This article outlines what to plant in a Colorado greenhouse, when to plant it, and how to manage environment, soil, pests, and harvests so you can eat fresh every month of the year.

Understanding Colorado greenhouse constraints and advantages

Colorado conditions vary by elevation and location, but some general features matter for greenhouse planning and crop selection:

• High daytime light intensity and strong UV, especially at elevation.
• Wide diurnal temperature swings: hot days, cold nights.
• Very low absolute humidity in many regions.
• Short outdoor growing season for warm-season crops without protection.

Advantages of a greenhouse in Colorado include extra light during shoulder seasons, the ability to trap daytime heat, and very fast growth rates in spring and fall when temperatures are moderate.
Practical takeaway: choose crops that match your greenhouse thermal capacity (passive vs heated) and be prepared to add heat, light, or humidity for tender crops in the cold months.

Key greenhouse environmental targets by crop type

Cool-season leafy greens and herbs (spring/fall/winter)

• Day temperature: 55 to 75 F (13 to 24 C).
• Night temperature: 40 to 55 F (4 to 13 C) for hardy types; 50 to 60 F (10 to 15 C) prolongs growth and reduces bolting.
• Humidity: 50 to 70 percent keeps leaves turgid in dry Colorado air but avoid stagnant pockets.

Fruiting warm-season crops (tomato, pepper, cucumber)

• Day temperature: 70 to 85 F (21 to 29 C).
• Night temperature: 60 to 70 F (15 to 21 C).
• Light: 12 to 16 hours of strong light; supplemental LEDs often required in winter.
• Pollination: active pollination (buzz pollinators or hand vibration) is necessary when natural insect activity is low.

Root crops and brassicas

• Comfortable at cool temps; carrots and beets tolerate moderate frost if soil is insulated.
• Night temperatures above 40 F generally desirable for consistent growth.

Practical takeaway: prioritize crops that match the environment you can realistically provide. If you have only passive heat, focus on hardy greens, root crops, and herbs.

Best plants to grow year-round in a Colorado greenhouse

Below are categories and specific varieties that perform well in Colorado greenhouses. Where useful, I note thermal and light requirements, container sizes, and sowing cadence.

Leafy greens and salad crops (best year-round choices)

• Lettuce (Looseleaf and romaine): Varieties like Winter Density, Black Seeded Simpson, Buttercrunch. Sow every 2 to 3 weeks for continual harvest. Ideal for cool greenhouse benches or low shelves.
• Spinach: Bloomsdale Long Standing resists bolting. Direct sow or transplant; grows well through winter with mild heating.
• Kale: Winterbor, Red Russian. Very cold tolerant and a top pick for low-heat winter production.
• Swiss chard: Bright Lights is productive and ornamental; tolerates cool temps.
• Arugula and mache: Fast turnover crops for tight sowing windows and winter harvest.

Practical details: sow small blocks every 10 to 21 days, harvest outer leaves or cut-and-come-again methods. Maintain 50 to 70 percent humidity and good air circulation.

Asian greens and brassicas (fast, cold-tolerant)

• Bok choy, tatsoi, mizuna: rapid growth and tolerant of cool nights.
• Broccoli and cauliflower: start earlier in greenhouse and move to cooler sections for head formation; broccoli varieties bred for cool weather perform best.

Planting note: brassicas can be sown late summer into fall for a greenhouse winter harvest; watch for aphids and cabbage loopers.

Root crops (carrots, radishes, beets, turnips)

• Radish: Cherry Belle and French Breakfast mature in 3 to 4 weeks and are great for staggered sowing.
• Carrot: Nantes, Danvers 126 do well in deep raised beds or long containers (12+ inches depth).
• Beet: Detroit Dark Red – sow successively; can overwinter in soil with insulation.

Practical detail: use deep, loose soil mixes and consistent moisture. In winter, insulate beds with straw or use soil-warming cables for consistent germination.

Herbs (high-value, low-space)

• Perennial Mediterranean herbs: rosemary, thyme, oregano – need good drainage and slightly warmer, drier spots in the greenhouse.
• Tender annuals: basil (Genovese), cilantro, parsley. Basil requires higher heat and light; move to warm benches or provide supplemental heat in winter.

Harvest tip: frequent harvesting increases production. Keep humidity moderate to prevent fungal leaf issues.

Fruiting crops: tomatoes, peppers, cucumbers, eggplant (season-extension and year-round with heat and light)

• Tomatoes: Sungold (cherry), Juliet, Trust. Indeterminate, indorsed for greenhouse production. Consider grafted plants for disease resistance and vigor.
• Peppers: California Wonder, Jalapeno. Warm-loving; require night temps above 55 to 60 F.
• Cucumbers: Marketmore and greenhouse hybrids that are parthenocarpic (no pollination needed) are useful in tight insect conditions.

Practical constraints: these crops demand steady warmth and light. In low-energy setups they are best concentrated in the warm half of the year; with supplemental heating and lights they can be grown year-round.

Small fruits and specialty plants

• Strawberries: day-neutral varieties (Albion, Seascape) fruit continuously and do well in hanging troughs.
• Figs and citrus: possible in heavily heated greenhouses. Meyer lemon and potted figs will need winter temperatures maintained above 50 F and supplemental light.

Practical note: fruit trees in greenhouse require pruning, space, and attention to humidity and pollination. Reserve these for fully heated structures.

Microgreens and sprouts (fastest yields, greatest ROI)

• Microgreens (arugula, sunflower, pea shoots, brassica mixes) produce in 7 to 21 days and can be grown continuously on shelves with LED lighting.
• Sprouts require no soil and are harvestable in days–excellent in winter for fresh nutrition.

Practical takeaway: microgreens are the fastest way to produce high-value fresh greens year-round with minimal space.

Layout, containers, and space management

• Raised beds and long troughs: preferred for root crops and dense plantings; depth 12 to 18 inches for carrots and tomatoes in containers.
• Containers: tomatoes 5 to 10 gallon, peppers 3 to 5 gallon, herbs 1 to 3 gallon.
• Vertical space: use trellises for cucumbers and indeterminate tomatoes; install sturdy overhead supports.

Succession plan: schedule sowings every 10 to 21 days for quick crops, every 3 to 6 weeks for slower crops. Keep a planting calendar and seed inventory.

Water, soil, and fertilization specifics

• Soil: target pH 6.0 to 6.8 for most soil-grown crops. Use compost-amended mixes with good drainage.
• Hydroponics: pH 5.8 to 6.2 and monitor electrical conductivity (EC) regularly.
• Irrigation: drip irrigation with timers and moisture sensors conserves water and prevents disease. Avoid overhead watering in winter to limit fungal outbreaks.
• Fertilizer: balanced N-P-K for leafy growth early (e.g., 10-10-10), then higher potassium for fruiting. Reduce fertilizer rates in winter when growth slows.

Practical tip: because Colorado air is dry, foliar feeds and humidity can help herbs and tender greens hold moisture–but keep airflow strong to prevent mildew.

Pest, disease, and quarantine protocols

Common greenhouse pests: aphids, whiteflies, spider mites, thrips. Diseases include botrytis and powdery mildew.
Integrated pest management steps:

• Sanitation: disinfect tools, benches, and new plant stock. Use foot baths and limit outside contamination.
• Monitoring: sticky traps and weekly inspections.
• Biologicals: predatory mites, ladybugs, and beneficial nematodes where appropriate.
• Targeted organic controls: insecticidal soap, horticultural oils, and neem for minor outbreaks.

Quarantine new plants for 7 to 14 days before adding to the main crop area.

Heating, shading, ventilation, and light management

• Thermal mass: barrels of water painted dark absorb heat by day and release heat at night; very effective in Colorado.
• Insulation: double poly glazing, insulated curtains for night, and floor insulation help hold heat.
• Heating: small propane or natural gas heaters with venting are common. Electric heaters and heat mats for seedlings are also used.
• Ventilation: roof and side vents plus circulation fans prevent hot pockets and reduce disease.
• Shading: use shade cloth (30 to 50 percent) to prevent bolting and sunscald on hot days in spring and summer.
• Supplemental lighting: full-spectrum LED fixtures placed on racks and benches provide 12 to 16 hours for fruiting crops during short winter days.

Operational rule: ventilate aggressively when greenhouse temperatures exceed 85 F and shade when leaf temperatures or plant stress appears.

Sample month-by-month approach for a mid-elevation Colorado greenhouse

• December to February: focus on kale, spinach, mache, microgreens, herbs on heated benches. Use thermal mass and minimal supplemental lighting for leafy crops.
• March to April: start tomatoes, peppers, and cucumbers indoors under lights; increase ventilation; direct-sow radishes and carrots in beds.
• May to August: full production of fruiting crops; use shade cloth on the hottest afternoons; succession sow fast greens.
• September to November: sow fall brassicas, winter lettuce, and root crops for overwintering. Reduce fertilization and prepare insulation for cold months.

Final practical checklist for success

• Choose crops that match your heating and lighting budget.
• Build thermal mass and insulate; conserve heat before buying a large heater.
• Stagger sowings for continuous harvests and use microgreens to fill gaps.
• Use drip irrigation and monitor soil moisture rather than schedule watering solely by time.
• Scout for pests weekly and quarantine new plants.
• Keep a planting calendar and record of varieties that succeed in your microclimate.

Growing year-round in a Colorado greenhouse is a combination of selecting the right crops, matching them to the environment you can provide, and following disciplined cultural practices. With the right varieties, scheduled sowings, and attention to climate control, you can enjoy fresh greens, herbs, and even fruits throughout the year.