Those of us lucky enough to have a greenhouse know the importance of storing all the critical gardening materials on hand: potting soil, hand trowels and pruners, and a large stack of empty pots just waiting for the next prized orchid. You can find a surprising amount of space for hanging tools and sliding things under benches. If your greenhouse isn’t already overflowing with plants, you can almost treat it like a storage shed for all your outdoor projects.

Except that greenhouses are hot, humid, and full of pests. Most greenhouses are not climate-controlled, with conditions that fluctuate throughout the seasons. For all these reasons, here are the things you should never store in your greenhouse.

Sick Plants

A greenhouse may seem like the perfect place for a plant to recuperate, but it’s also an ideal environment for spreading pests and diseases to the rest of your plants. No matter how much you are tempted, sickly plants should be kept out of the greenhouse. All outdoor plants should be inspected and treated for pests before moving into a greenhouse.

Pesticides

Pesticides need to be stored in an environment that never gets colder than 40 degrees Fahrenheit or hotter than 90. Why? Some pesticides can combust—that is, catch fire—if they get too hot. Store your pesticides in a cool, dry, well-ventilated place to keep yourself safe.

Bird Seed And Garden Seeds

Greenhouses should not be used for long-term seed storage. Moisture can ruin seeds, especially if you have a leak in the greenhouse or accidentally spill a watering can. Many garden seeds need to be stored at a cool temperature for the best germination. And finally, your seeds may completely vanish if rodents find their way in. Any seeds you keep on hand for short periods should be stored in an airtight container.

Paint Cans

If you’re looking for a spot to store your leftover porch paint, look elsewhere. The temperature fluctuations in a greenhouse—especially if it gets below freezing in winter—can ruin your paint.

Paper And Cardboard

This isn’t the spot to stack all your leftover cardboard plant trays, boxes, or other papers. The humidity will cause the paper to mold and break down.

Tools That Aren’t Rust-Resistant

Keep a few stainless steel or plastic hand tools in the greenhouse for potting up your plants, but don’t want to store your favorite antique tools here. Humidity will rust metal, and the fluctuating conditions can split wood.