Greenhouse Planting Calendar: Build a Schedule for Your Climate

A greenhouse changes growing conditions, but it does not create one national planting calendar. Outdoor temperature, day length, cloud cover, greenhouse design, heating, ventilation, crop, and cultivar all affect timing.

Sierra Greenhouse has not tracked hundreds of greenhouses or measured the yield increase previously claimed on this page. The old zone-by-zone promises and invented return-on-investment examples have been removed. This guide shows how to build a calendar from local observations and crop information.

Hardiness zone is only one input

The USDA Plant Hardiness Zone Map is based on average annual extreme minimum winter temperature. It is useful for perennial cold hardiness, but it does not tell you a greenhouse's spring frost date, daily light, summer heat, or inside temperature.

For greenhouse scheduling, collect:

• local first and last frost-date ranges;
• day length and seasonal cloud patterns;
• measured greenhouse daytime and overnight temperatures;
• the lowest temperature the crop can tolerate;
• germination, transplant, and maturity information for the cultivar;
• heating, lighting, and cooling capacity; and
• the date when an outdoor bed or market needs the plant.

Use several years of local climate information where available, then keep your own greenhouse record. A calendar should be adjusted after each season.

Start with a backward-planning worksheet

For each crop, record the target harvest or transplant window and work backward:

| Field | What to enter | | --- | --- | | Crop and cultivar | Use the exact seed or plant label | | Destination | Greenhouse harvest, outdoor transplant, or container | | Target window | A range, not one guaranteed date | | Days to maturity | Note whether the source counts from sowing or transplant | | Propagation time | Germination plus time to transplant size | | Temperature needs | Germination, growing, and cold-injury guidance | | Light needs | Natural-light season and any measured supplemental-light plan | | Space period | Bench or bed area occupied over time | | Succession interval | Trial interval between small plantings | | Actual result | Sowing, emergence, transplant, harvest, and loss dates |

Add contingency time for slow germination, cloudy periods, transplant recovery, and weather delays. Avoid filling every bench on paper; working access and crop separation still matter.

A month-by-month planning framework

The prompts below assume a Northern Hemisphere calendar. They are operational checks, not zone-specific planting guarantees.

January

• Review the prior year's temperature, energy, pest, and harvest records.
• Check germination equipment and propagation-space limits.
• Start only crops whose light and temperature needs the system can support.
• Inspect heaters, alarms, vents, and water lines before severe weather.

February

• Confirm local outdoor transplant windows before starting long-lead crops.
• Compare actual bench space with the number of planned seedlings.
• Begin small successions of suitable cool-season crops if measured conditions support them.

March

• Expect larger daytime swings and verify automatic vent operation.
• Harden plants gradually for outdoor conditions when appropriate.
• Record which areas warm first and whether irrigation demand is changing.

April

• Recheck frost risk rather than relying on a single average date.
• Separate incoming plants for inspection before mixing them with established crops.
• Prepare shade and cooling equipment before it is urgently needed.

May

• Transition outdoor transplants according to local weather and crop tolerance.
• Review spacing as fruiting crops expand.
• Adjust irrigation from root-zone observations rather than calendar alone.

June

• Monitor canopy-level highs, not only the doorway thermometer.
• Use measured light and crop response to decide whether shade is needed.
• Maintain harvest and succession records so gaps and crowding are visible.

July

• Prioritize ventilation, irrigation uniformity, pest scouting, and worker heat safety.
• Start fall crops only after checking propagation temperature and future space.
• Note cultivars that tolerate the site's summer conditions.

August

• Work backward from local fall light and temperature conditions.
• Clean empty areas before the next crop enters.
• Inspect glazing, seals, controls, and heaters while repairs are easier.

September

• Move cold-sensitive crops according to measured conditions and forecast risk.
• Reduce irrigation as demand falls; do not carry a midsummer schedule into autumn automatically.
• Decide which winter area, if any, is economical and safe to heat.

October

• Test heating, alarms, backup plans, and safe fuel or electrical operation.
• Manage evening moisture and inspect for condensation around dawn.
• Focus winter space on crops suited to available light and temperature.

November

• Compare growth with the shortening natural-light period.
• Keep paths and vents clear and inspect for persistent wet areas.
• Record energy separately for any heated crop trial.

December

• Keep winter plantings conservative unless the environment is measured and controlled for the crop.
• Review seed inventory, cultivar notes, and failures before planning the next year.
• Schedule structural, electrical, and climate-system maintenance.

Group crops by environmental fit

Instead of ranking crops by a universal profit figure, group them by the conditions your greenhouse can provide.

Cool-tolerant candidates

Many leafy greens, brassica greens, and some herbs can suit cooler production, but cultivar limits and available light still matter. Use extension and seed supplier guidance and test a small planting first.

Warm-season fruiting crops

Tomatoes, peppers, cucumbers, and similar crops generally need more warmth, light, space, training, and often pollination management. Count the full period that a mature crop occupies the greenhouse, not only days to first harvest.

Propagation crops

Seedlings may need warm media while the surrounding greenhouse is cooler. Size heat mats, lights, trays, and electrical circuits for the planned propagation area and follow equipment instructions.

Use succession planting as a local trial

Sow small batches at a recorded interval. Track emergence, losses, harvest start, harvest end, and usable quantity. If batches overlap too much, lengthen the interval; if harvest gaps appear, shorten it cautiously or adjust batch size.

Seasonal changes mean an interval that works in spring may not work in autumn. Treat the record as a local planning tool, not a permanent formula.

Evaluate winter production without a promised ROI

List crop revenue or household value separately from heat, light, supplies, labor, and losses. Model more than one utility-price and weather scenario. A profitable commercial crop in a specialized structure does not prove that the same crop will pay back a hobby greenhouse.

The University of Minnesota's deep winter greenhouse program publishes design, production, and enterprise-budget resources for that specific passive-solar system. Those findings should not be generalized to every greenhouse.

Official planning references

• USDA Plant Hardiness Zone Map
• University of Minnesota Extension: Extending the growing season
• University of Minnesota Extension: Deep winter greenhouses

Start with a small, dated plan and write down what actually happened. After one season, your own temperature, planting, harvest, and cost records will be more useful than a nationwide calendar that ignores the greenhouse in front of you.