What To Plant First In An Alaska Greenhouse

This article explains what to plant first in an Alaska greenhouse, with practical, climate-specific guidance, planting timelines, crop suggestions, and step-by-step actions you can take the first season. The goal is to help you get productive quickly while avoiding common mistakes in cold, low-light environments.

Understand the Alaska greenhouse context

Alaska covers a wide range of climates: coastal maritime zones (Anchorage, Juneau), continental interior (Fairbanks), and the Aleutians. Your greenhouse strategy must match your local realities: winter darkness, late springs, extreme cold, and short natural growing seasons. A greenhouse does not automatically make your growing season like the Lower 48. It gives you more control, earlier starts, and the ability to grow tender crops later into fall and early winter — but you still need to choose crops and systems that fit limited light and potential temperature swings.

Key constraints to plan for

Cold nights and low winter light are the two biggest constraints. In winter months, supplemental lighting is often necessary for vigorous growth. Heat sources or thermal mass are required if you want to maintain germination and growth temperatures through late fall and early spring. Snow load and wind protection are structural concerns unique to Alaska and must be part of the plan before planting.

Which crops to plant first: principles

Start with crops that are:

Cold-tolerant or cold-hardy.
Fast-maturing for early harvests.
High value per square foot (greens, herbs).
Easy to start from seed inside the greenhouse.
Low light tolerant (for early spring/late fall).

Those principles lead to a predictable set of first crops that bring early success and steady harvests while you refine heat and light systems for more demanding crops later.

Best first crops for an Alaska greenhouse

Below is a prioritized list of crops to plant first and why they work in Alaska greenhouse conditions.

Salad greens (leaf lettuce, arugula, mizuna, tatsoi) — Fast germination (5-14 days), mature in 30-45 days, tolerate cool soil (40-50degF for germination for many varieties), harvest continuously by cutting leaves.
Spinach — Cold-hardy and fast, tolerates low light better than many vegetables. Sow early and successively for spring harvests.
Kale and Swiss chard — Very cold-tolerant, highly productive, and nutritious. Kale can thrive near freezing temperatures.
Radishes — Very fast (20-30 days), excellent for early morale and quick turnover; show you how the greenhouse microclimate performs.
Peas (snow peas, shelling peas) — Cool-weather climbers that can be sown as soon as the soil is workable; they add nitrogen to the soil and are one of the first crops to produce in spring.
Scallions and bunching onions — Easy to start from seed or sets; mature quickly and provide a persistent harvest.
Herbs (chives, parsley, cilantro, dill) — Many herbs tolerate cooler temperatures and boost household use; chives are very hardy.
Microgreens and sprouts — Extremely quick turnaround (7-21 days), high yield from small space, and an easy first harvest while building soil fertility.
Root crops with short roots: baby carrots, baby beets, small radishes — Choose short-root varieties for shallow greenhouse beds and faster harvests.
Overwintered garlic (plant in fall) — If you have a fall-planted plan, garlic planted in autumn can overwinter and produce a substantial harvest the following mid-summer.

Varieties and cold-tolerant options

Choosing varieties bred for short seasons or cold tolerance increases success. Look for varieties labeled “cold-hardy,” “short-season,” or specifically known in northern gardens. Examples commonly recommended in cold climates include: cold-tolerant lettuces, “Lacinato” kale, “Winterbor” kale, early maturing peas, and short-root carrot varieties. For tomatoes later in the season, opt for early, determinate, or dwarf types (e.g., “Stupice” or “Sub Arctic Plenty”) and be prepared to provide supplemental heat and light.

Step-by-step plan to plant your first greenhouse crops

Assess your greenhouse environment: measure daytime and nighttime temperatures, soil temperature at 2-3 inches, and light levels on an overcast day.
Prepare beds and soil: use raised beds or deep containers filled with a well-draining mix amended with compost. Aim for a soil pH between 6.0 and 7.0.
Choose your first crop palette: start with a mix of salad greens, spinach, radishes, scallions, and peas.
Sow seeds at recommended depths and spacing: most lettuces 1/8-1/4 inch deep, radishes 1/2 inch, peas 1-2 inches. Follow packet instructions and thin to final spacing when seedlings establish.
Manage temperatures: maintain seed germination temps (typically 40-75degF depending on crop). Use row covers, heat mats for trays, or passive solar thermal mass barrels if nights dip too low.
Provide light as needed: in early spring or late fall, add LED supplemental lighting for 8-12 hours to prevent leggy growth; greens need less intense light than fruiting crops.
Water carefully: use consistent, moderate watering; greenhouse soils can dry quickly during sunny days. Avoid overly wet conditions that encourage fungal diseases.
Ventilate during warm days: open vents or doors to prevent overheating and damp, stale air that leads to mildew.
Practice succession planting: sow small amounts every 10-14 days for continual harvests.
Monitor for pests and diseases: check underside of leaves for aphids and whiteflies, and use row covers or biological controls when possible.

Timing: when to sow in Alaska

Timing depends on location and greenhouse capabilities. With an unheated greenhouse, you can generally start cold-tolerant greens and peas as soon as the soil is above freezing and workable — often early April in southern coastal zones, and late May in interior regions. Heated greenhouses allow sowing weeks to months earlier. Use soil temperature rather than calendar date:

Greens: sow when soil is 35-45degF for hardy varieties; germination works but will be slow at the low end.
Peas: sow at 35-40degF soil temperatures.
Radishes: sow when soil is 40-50degF.
Potatoes (in containers): plant seed potatoes when soil consistently reaches 45-50degF.

If you use grow lights and heated benches, you can start transplants up to 6-8 weeks earlier than standard greenhouse sowing times.

Practical greenhouse systems for Alaska

Passive solar greenhouses with thermal mass (barrels of water, stone beds), insulated north walls, and double poly or polycarbonate glazing perform very well. Consider the following practical systems:

Thermal mass barrels painted black to absorb heat by day and radiate by night.
Compost-heated benches: use active hot compost trenches under beds to add warmth.
Double-inflated poly with blower for insulation in winter.
Small wood stove or efficient propane heater for emergency frost protection — ensure proper venting and safety.
LED supplemental lighting for low-energy, targeted light boosts.

Common mistakes and how to avoid them

Mistake: Planting high-heat crops (indeterminate tomatoes, peppers) first expecting greenhouse warmth. Fix: start with cold-tolerant crops; bring in tomatoes after the greenhouse proves it can deliver night temps consistently above 50degF and light is adequate.
Mistake: Overwatering in low-light winter months. Fix: check soil moisture with finger or probe and reduce frequency; use deft drainage.
Mistake: Neglecting ventilation leading to fungal outbreaks. Fix: install automatic vent openers or schedule daily ventilation during warm sunny days.
Mistake: Not insulating north wall or glazing well, causing heat loss. Fix: add insulation or thermal curtains for night-time retention.

Practical harvest and rotation tips

Harvest young leaves frequently to encourage regrowth, especially for salad mixes. Rotate bed positions seasonally to avoid nutrient depletion and disease build-up. Interplant peas with low-growing salads to use vertical space efficiently. Keep a simple log of planting dates, germination rates, and harvests — Alaska weather varies year to year and data will help refine your schedule.

Final takeaways

Start simple: prioritize fast, cold-hardy, high-value crops like salad greens, spinach, kale, radishes, peas, scallions, and microgreens. Measure actual soil and air temperatures before sowing, prepare soil with ample compost, and manage heat and light incrementally rather than relying on one big system. Use succession sowing and small beds to build confidence and early yields. With thoughtful variety choices, modest supplemental heat and light, and good ventilation, an Alaska greenhouse can produce steady, early-season vegetables and supply fresh greens through much of the year.