Are they long stem or short? Assuming the former, this article from Suite 1010 suggests this along with its other nifty ideas: “For large bundles of flowers like wheat stalks, avena or bromus I cover the bunch of flower heads with a small plastic bag from the grocery and use a twist tie to secure the bag. I don’t worry about covering the stalk/stem part. You can place multiple bundles of stalk type flowers lengthwise in a large box with a lid. Store in a cool, dry place when not using.”