iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
In an unheated or lightly managed greenhouse, start with cool-season crops: spinach, lettuce, kale, arugula and other leafy greens. Carrots and some other root crops can also work when there is enough time for them to mature. The right planting date depends on your local frost pattern, daylight, variety and the temperatures inside your greenhouse—not just the season on the calendar.
Which crops are most dependable?
Cold-tolerant leafy crops are the safest starting point for shoulder-season growing. University Extension guidance includes them in protected-culture, fall or early-spring production plans, though the specific windows vary by region and structure.
| Crop | Why consider it | Timing and harvest considerations |
|---|---|---|
| Spinach | Included in fall high-tunnel guidance and in protected winter-growing advice. | Plan sowing around local conditions and the days to maturity for your variety. Some low-tunnel guidance describes carrying spinach through winter with protection; that is not a guarantee for every greenhouse. Iowa State Extension and Cornell High Tunnels. |
| Lettuce | A common protected-culture green, with spring and fall planting windows in Virginia Tech’s regional guide. | Choose a cold-tolerant variety and use the local planting window; consider baby-leaf harvest if conditions are likely to shorten the growing period. Virginia Cooperative Extension and Cornell High Tunnels. |
| Kale and related greens | Kale appears in protected-culture and overwintering guidance. | Establish plants while they still have enough light and time to grow; protection can help them persist, but does not ensure active growth through cold, short days. Cornell High Tunnels and University of Maryland Extension. |
| Arugula and other leafy crops | Arugula is among Maryland’s fall crops described for overwintering with protection; Cornell also covers cold-hardy tunnel greens. | Use local guidance to judge whether to sow or transplant and when to expect harvest. University of Maryland Extension and Cornell High Tunnels. |
| Carrots and other root crops | Listed in high-tunnel or fall-production guidance, but less forgiving of a too-short growing window. | Check the variety’s maturity period and leave enough time before cold and short days slow growth; a late planting may yield small roots. Purdue Extension and University of Maryland Extension. |
For a first planting, prioritize spinach, lettuce or kale, then add arugula or carrots according to your space and local season. Sow successions when the calendar allows so harvests are spread out rather than arriving all at once.
Recommended Free Tools
How should you time early-spring and late-fall planting?
For early spring
Use a planting guide for your region and work from expected local frost conditions, the variety’s maturity time and the temperatures your structure actually maintains. Virginia Tech’s home-garden guide gives windows by hardiness zone and cautions that killing-frost dates vary with local conditions and from year to year; it is Virginia guidance, not a universal calendar. See Virginia’s Home Garden Vegetable Planting Guide.
#1 Best Overall
- Upgraded with Adjustable Ventilation - Gardzen seed starter tray has been newly upgraded with two air vents added to the top, allowing you to easily adjust the ventilation for optimal seed growth. Say goodbye to stagnant air and hello to thriving plants!
- High Quality and Durable - These seedling starter trays are made from premium plastic material, ensuring long-lasting use for all your seed starting needs. Comes with thoughtfully attached stickers, you can achieve a tighter fit of dome and base for maximum efficiency.
- 40-Cell Capacity - Each seed starter kit in our set comes with a generous 40-cell capacity, providing ample space for all your seeds to sprout and thrive. Whether you're a beginner or experienced gardener, this plant starter kit is perfect for starting your own garden paradise.
- Easy to Manage Kits - The 40-cell insert tray provides a simple, straightforward way to start seeds and grow plants from cuttings. The drain hole at the bottom of the seed tray prevents over watering. The clear dome allows you to clearly see the growth status.
- Versatile and User-friendly - This seed germination kit is not only suitable for starting seeds but also perfect for propagating cuttings and nurturing young plants.
For late fall and winter carryover
Give crops time to establish before daylight declines sharply. The University of Nevada, Reno Extension says growth slows dramatically when day length drops below 10 hours; that is a daylight threshold, not a fixed date that applies everywhere. Maryland Extension likewise advises planting early enough for establishment as days shorten. Use a locally relevant schedule rather than transferring a Nevada or Maryland timing example to another latitude. University of Nevada, Reno Extension and University of Maryland Extension.
What protection can—and cannot—do
A greenhouse or high tunnel can extend the growing season, but an unheated structure is not a source of supplemental heat or light. It may warm quickly in sunshine while offering limited protection overnight, so check actual daytime and nighttime temperatures inside the structure. Nevada Extension discusses these high-tunnel temperature swings in its winter guidance. Read the high-tunnel winter guidance.
Rank #2
- EASIER SEED STARTING: Our Burpee SuperSeed tray with 36 flexible pop-out cells is designed to simplify indoor seed starting for all your favorite vegetables, flowers and herbs. Just add seed starting mix, seeds, water and light to get growing! Rows are labeled alphanumerically for seedling identification with included Plant-o-Gram diagram. Tray dimensions: 11.5" x 10-3/8" x 2-1/4"
- SMARTER WATERING SYSTEM: Molded corner slots in each cell improve drainage and soil aeration to set your seeds up for germination success. Deep channels in the watering tray draw excess away from the cells, while the raised perimeter edge keeps water contained in the tray - no spills! Seed tray side handles make it easy to lift and pour off excess water or check seedlings daily.
- SIMPLER TRANSPLANTING: Soft food-grade silicone cells cradle seedlings and gently flex to pop out when it’s time to transplant into your outdoor garden! This system is specially designed to reduce stress on your seedlings, so you don't damage their roots. After transplanting, trays are easy to clean and reuse or simply store for next growing season. Top shelf dishwasher safe.
- SEED STARTER TIP: Many favorite vegetables, including peppers and tomatoes, must be started indoors before warmer weather arrives. Start pepper seeds 8-10 weeks before your area’s average last frost date, and tomato seeds 6-8 weeks before last frost. Check your Burpee seed packets for instructions on when and how to plant any of your herb, flower and vegetable seeds.
- 100% GUARANTEED: Burpee is committed to the success of all gardeners. We treat each order with care to ensure healthy seeds, plants, soil mixes and gardening supplies are packaged and sent in excellent condition. If you are unsatisfied with your purchase, we aim to make it right!
Structures and covers are not interchangeable: a greenhouse, high tunnel, low tunnel and cold frame differ in how they protect crops. Iowa State’s season-extension advice specifically concerns low tunnels. Virginia Tech says row covers or cold frames may extend the expected planting and harvest window by two to four weeks in the context of its Virginia guide; treat that as a regional estimate, not a promise for every crop or greenhouse. Iowa State Extension on low tunnels and Virginia Tech’s planting guide.
Quick Recap
Best Value
- 【Keep an eye on your plant】: The only design in the market- High quality clear plastic trays of this seed grow kit make it easier to observe your plants without interrupting the process.
- 【Total control】: Adjustable vents of this seed trays allow you to regulate the temperature and humidity of your seedling environment, so you have total control over the germination process.
- 【Perfect for the heat mat】: With its excellent resistance to high and low temperature, these seedling trays are strong enough to be used on a heat mat and no-worry melting.
- 【Perfect size for large seed】: 1.5 inch square for each cell makes these seed trays are suitable for large seeds, such as potatoes,tomates,perpers, eggplants and so on. 6 trays equivalent to a 1020 flat.
- 【Package include】5 x Seed Tray, 5 x Watertight Base Tray, 5 x Humidity Dome, 10 x Plant Labels (A must have for seedling).
Rank #4
- Pro Grow Lights with Advanced Chips: Equipped with 56 high-efficiency beads per tray, these LED strips simulate natural sunlight for optimal seedling growth. Adjustable brightness and timer functions let you customize lighting for every plant stage, promoting faster, healthier growth—perfect for herbs, flowers, and more
- Simple Self-Watering System: Ensures consistent moisture with an efficient design that prevents overwatering or drying out. One watering supports seeds from germination to transplanting, making gardening stress-free and beginner-friendly
- Built for Practicality and Durability: Made from high-density, BPA-free PET material, the 1.5mm thick dome and base tray lock in temperature and humidity while providing ample space for seedlings. Designed for long-lasting performance, this kit is a reliable choice for years of use
- Adjustable Humidity & Optimal Ventilation: Features two adjustable vents for precise humidity and airflow control, ideal for every growth stage. The 60-cell tray’s enlarged drainage holes remove excess water, maintaining optimal moisture and air circulation for healthy roots
- Double the Value, Double the Growth: Includes 2* humidity domes, 4* humidity vents, 2* 60-cell seed trays, 2* base trays, 2* capillary mats, 2* plant stands, a grow light system (4 LED strips, controller, detachable adapter), 20 plant labels, and 2 gardening tools. Packaged beautifully with a user manual, this kit is perfect for larger projects or sharing with a fellow plant lover
Rank #3
- 【360°Spectrum Seed Starter Tray with Grow Light】 The Larger 360°full-spectrum plant grow light in our seed start tray promotes healthier roots, faster germination, stronger seedlings. Seed starter kit with 4 full spectrum strip, mounted on the dome of garden plant starter kit. White & blue grow light helps seedlings grow faster and healthier. 3 lighting modes, 3 timer settings (3H/6H/12H), 5 brightness modes fully adjustable to your plants' needs. Your journey from seed to harvest starts here!
- 【Higher Dome & Deeper Cell Trays】80 powerful lamp beads (40 per tray) provide full & even plant light for every seed. More grow lights, more growth, this is our secret to healthier seedlings. Give every plant starter room to grow. 9cm tall humidity dome lets seedlings grow taller indoors. 1.96in deeper seed cell trays help build stronger roots for healthier plants. 0.31in drainage holes prevent overwatering and root rot. Every cell of seed starting kit is engineered for a perfect start.
- 【Adjustable Humidity & Grow Light】Upgraded seed starting trays with adjustable grow light timer & ventilation vents, for superior seed starting & precise humidity control. Remote indicator: red for 3-hour timer, blue for 6-hour, red & blue for 12-hour. With this greenhouse germination kit, you can add grow light strips to cultivate seeds. Easily adjust vent covers to change the humidity of plant starter trays, adjust moisture for different growth stages.
- 【Durable ABS & Clear Dome】 Our seeding starter trays are made of high-quality, thickened, unbreakable ABS plastic. It is a great seed starter kit, anti-UV, corrosion-resistant, water-saving, and dry-resistant. Clear seed trays let you monitor soil condition, while clear dome allows tracking seedling growth without lifting it. Super lightweight, easy to carry & clean, our reusable seed starter tray is ready for the next season. Plant germination trays — from seeding tray to harvest.
- 【Versatile for All Plants】Seed starter trays powered by USB or plug-in adapter, 2 ways to use seedling trays (adapter included). Our seed starter tray create ideal growing conditions for a wide range of plants—flowers, vegetables, fruits, tomatoes, herbs, and more. Whether you're beginner or seasoned gardener, this planting trays let you learn and get fun of planting at home with your family.
A practical crop-selection checklist
- Choose cold-tolerant varieties and check the expected days to maturity on the seed packet.
- Look up local spring and fall planting windows; adjust for your likely frost dates and the daylight available.
- Decide whether you want baby leaves or full-size crops, since the intended harvest stage changes how much growing time you need.
- Monitor temperatures inside the greenhouse, especially overnight, and add suitable protection if needed.
- Use succession sowing where the local calendar leaves enough time for another planting.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
