Beating the Autumn Chill: How Humidity Domes Help Seeds Thrive in Cooler Weather

Even though it's autumn in Australia, seed starting dreams don't have to hibernate! Cooler weather can pose a challenge, but a simple tool called a humidity dome can be your secret weapon for successful seed germination during these chillier months.

What is a humidity dome, and how does it work?

Imagine a clear plastic cloche placed over your seed tray. That's a humidity dome in essence. It traps moisture evaporating from the growing medium, creating a mini greenhouse effect. This benefits seeds in two key ways:

Maintaining Moisture: Cooler temperatures often lead to slower evaporation. However, homes can be surprisingly dry, especially with heating systems running. A humidity dome reduces evaporation further, ensuring the delicate seeds stay consistently moist – a crucial factor for germination.
Boosting Temperature: The dome acts as a mini insulator, trapping some of the heat radiating from the soil and the surrounding environment. This slight temperature increase can be just enough to nudge those cool-weather-loving seeds into germination.

The Ideal Germination Environment

While specific requirements vary by seed type, most seeds prefer a humidity level around 70-80% for germination. A humidity dome effectively creates this microclimate.

Temperature is another crucial factor. Many cool-season vegetables commonly grown in Australia, like lettuce, spinach, and broccoli, germinate happily in the 13-18°C (55-65°F) range. Others, like tomatoes and peppers, benefit from slightly warmer temperatures, ideally around 21-24°C (70-75°F). A humidity dome can provide that crucial bump, especially when used in conjunction with a heat mat placed underneath the seed tray.

Microgreen Broccoli Example

If you are growing your microgreens in an uncontrolled environment, then you could really benefit from using a clear humidity dome to boost growth. We keep our microgreen brocolli under dark for 3 days, then on day 4 we swap-out the blackout dome with a 6" clear humidity dome. This gives a great boost to the broccoli growth. We leave the humidity dome on for a day before removing it.

Benefits Beyond Germination

Humidity domes offer more than just a germination boost. They also:

Protect Seedlings: The dome acts as a physical barrier, safeguarding delicate seedlings from drafts, pests, and accidental bumps.
Reduce Watering Needs: Less evaporation translates to less frequent watering, minimizing the risk of overwatering, which can be detrimental to seedlings.

Remember: Don't keep the dome on forever. Once seedlings emerge, gradually introduce them to lower humidity by cracking open the vents on the dome (if it has any) or removing it entirely for short periods. This helps them acclimate to the ambient environment before transplanting.

With a little help from a humidity dome, you can give your seeds the warm, moist haven they need to sprout successfully, even when the weather outside isn't cooperating. So, grab your domes, and get ready to enjoy a thriving crop of seedlings come spring!