How to Seal Agar Plates for Long-Term Use
- Harold Evans
- Aug 22, 2025
- 2 min read
Updated: Mar 6
Agar plates are one of the most important tools in mushroom cultivation, but only if they’re sealed and stored properly. Parafilm is the standard choice for sealing agar plates. It stretches to conform to the seam, creates an airtight barrier, and won't contaminate your culture. Sealing your plates keeps them clean, prevents contamination, and makes sure they stay viable until you’re ready to use them.
Why Sealing Matters
Prevents contamination by sealing the vulnerable seam where the lid meets the base.
Keeps moisture in, so the agar doesn’t dry out.
Extends shelf life when storing plates for future projects.
What You’ll Need
Parafilm (preferred)
Plastic wrap or grafting tape (acceptable alternatives)
Scissors to cut strips
Step-by-Step: Sealing an Agar Plate
Cut Your Strips
Cut your Parafilm into strips about ½" to 1" wide. The width should be enough to comfortably cover the seam where the lid and base meet.
Grip the Plate
Hold the plate between your index and middle finger, with one finger resting on the flat top of the lid and the other on the bottom. This creates a stable grip while keeping the plate relatively flat so the culture inside doesn’t slide or shift. Your thumb rests against the side of the seam, ready to press the Parafilm into place.
Anchor the Parafilm
Place one end of the strip along the seam where the lid meets the base. Use your thumb to press and hold it firmly against the edge of the plate.
Stretch and Wrap
With your free hand, gently stretch the Parafilm while guiding it around the plate. Rotate the plate smoothly using the hand holding it, keeping it flat to avoid jostling the culture. Maintain steady tension so the strip seals evenly without gaps.
Overlap and Finish
When you reach the starting point, overlap the strip slightly and press it down to complete the seal. The wrap should feel snug and secure, but not so tight that it bends the plastic lid or base.
Storage Tips
Short-term: Store sealed plates at room temperature while your culture grows.
Long-term: Place sealed plates in a clean container in the fridge (never the freezer) to extend viability. Properly sealed plates can stay viable for months, letting you maintain a library of clean cultures for future projects.
Conclusion
Sealing agar plates is a simple but essential skill in mushroom cultivation. With the right grip and a little practice, you’ll be able to seal plates quickly and securely, keeping your cultures clean, hydrated, and ready for future transfers.
Master Storage, Multiply Your Cultures
Once you've learned proper sealing technique, you can maintain a culture library for months. Each plate becomes a launching point for multiple transfers and projects.
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