Your greenhouse helped carry tender seedlings through cool spring nights. Now May brings longer days, warmer afternoons, and stronger sunlight. Without a seasonal maintenance plan, that protected growing space can heat up quickly, stressing your plants.

The good news is that a few smart adjustments can make a big difference. By checking ventilation, adding shade, improving irrigation, and rotating crops at the right time, you can keep your greenhouse productive as summer approaches. This May maintenance masterclass will help you prepare with confidence.

1. Check Ventilation Before Heat Builds Up

The weather can change fast. A cool morning can turn into a warm afternoon, and greenhouse temperatures may rise much higher than outdoor temperatures. Once outdoor temperatures reach the 70s, passive airflow may not be enough to protect tender plants from heat stress.

Start by testing roof vents, side vents, louvers, circulation fans, exhaust fans, and thermostats. Clean away dust and pollen, tighten loose hardware, and make sure moving parts open smoothly. If your greenhouse uses automatic vent openers, confirm they respond properly as temperatures rise.

Pro tip: Inspect louvers and exhaust fans early in the month. Clean the fan blades, test the thermostat settings, and lubricate the hinges or arms as needed. If you are building a greenhouse, review Gothic Arch’s greenhouse-building instructions for helpful placement guidance.

 2. Add Shade to Prevent Leaf Scorch and Bolting

As daylight strengthens, some crops struggle with the extra heat and light. Lettuce, spinach, arugula, cilantro, and other cool-season plants may bolt quickly. Even warm-season crops, such as tomatoes and peppers, can suffer from transplant shock if light levels climb too fast.

Shade cloth helps soften intense sunlight, reduce heat buildup, and extend harvest windows. Many growers use 30% to 50% shade depending on crop type, region, and greenhouse exposure. A lower shade percentage may work well for tomatoes and peppers, while tender greens often benefit from stronger protection.

 3. Adjust Watering for Faster Growth and Warmer Days

Plants grow quickly in May, but water also evaporates faster. A watering routine that worked in April may no longer be enough. Check container moisture more often, especially for seedlings, hanging baskets, grow bags, and crops near greenhouse edges, where heat can build up.

Morning watering is usually best because it gives foliage time to dry before night. For better efficiency, consider drip irrigation, timers, capillary mats, or misting systems. These tools deliver water more evenly, help reduce waste, and keep roots consistently moist.

Quick tip: Add mulch to larger containers or raised beds inside the greenhouse to slow surface evaporation. For smaller growing spaces, explore greenhouse options

4. Rotate Spring Crops and Make Room for Summer Favorites

May is a bridge month in the greenhouse. Cool-season crops are finishing, while heat-loving plants are ready to take center stage. Harvest remaining lettuce, kale, radishes, peas, spinach, and cilantro before they bolt. Then refresh beds or containers for tomatoes, peppers, cucumbers, basil, okra, eggplant, beans, and squash.

Before moving summer crops into permanent spots, make sure nighttime temperatures are stable. Many warm-season plants prefer nights above 50°F. If your region still has cool evenings, keep transplants protected and avoid rushing the final move.

• Harvest now: arugula, spinach, cilantro, snap peas, spring onions, lettuce, and radishes.
• Transplant when nights are warm: tomatoes, peppers, eggplant, basil, cucumbers, and okra.
• Direct sow where space allows: beans, squash, melons, and corn.

Need help improving your layout? Gothic Arch’s custom greenhouse design services can help you plan benches, shelving, irrigation zones, and seasonal crop flow.

 5. Test Climate Controls Before Peak Summer

May is the right time to test automation before the hottest weather arrives. Thermostats, humidity sensors, timers, fans, vents, shade systems, and irrigation controls should all be checked while the season is still manageable.

Advanced greenhouse control systems make it easier to monitor temperature, humidity, airflow, and watering schedules. For growers managing larger spaces or high-value crops, automation can reduce guesswork and support consistent production.

Grow With Confidence: Trusted Since 1946

At Gothic Arch Greenhouses, we do more than provide greenhouse structures. We help gardeners and growers build productive spaces that support every season. Whether you are maintaining a hobby greenhouse, planning a commercial growing operation, or improving climate control, our team is here to help.

For more seasonal tips, product guidance, and growing ideas, visit the Gothic Arch Greenhouses blog. With the right May maintenance plan, your greenhouse can move smoothly from spring protection to summer production.

Further reading: Explore Gothic Arch greenhouse kits, ventilation systems, irrigation supplies, shade accessories, portable greenhouses, and custom greenhouse design options at GothicArchGreenhouses.com. Happy May, growing!