DIAGNOSIS Wet or stringy grass building up under the deck is common, especially in damp conditions. That buildup reduces cutting quality, strains the blades, and can lead to rust.
FIX The safest and most effective method is to use a deck cleaning port or a lift. 1) Park on a hard, level surface and turn off the mower. Remove the key AND remove the battery packs. 2) If your Z6 has the deck wash port (a hose connector on the deck), hook a garden hose to it, raise the deck to its highest setting, and run the blades for about two minutes. The water will help soften and flush out the buildup. 3) If you don't have the port, or for a deeper clean, you'll need to safely lift the front of the mower (using a proper jack, not just car ramps) to access underneath. Use a plastic scraper or putty knife to knock off the big chunks, then hose it down.
IF THAT DIDN'T WORK For stubborn, dried-on clay-like grass, you may need to remove the deck. It's a bigger job but allows for a thorough scrape, wire brush cleaning, and inspection of the blade spindles. Make sure to support the deck securely when unbolting it.
HEADS UP Never, ever stick your hand or a tool under the deck to clean it unless you have physically removed the battery packs. The blades can spin from residual energy or accidental contact, even with the key off.