This avocado planter can float an avocado seed submerged in water by 70%. Planter consists of 2 parts.
Bed is for avocado itself, without scaling can fit an avocado up to 37mm in dia at the bottom. If your seed is bigger, just scale up the model. Try to print without infill.
Floater is a ballast cap that helps with floating and not flipping. Without scaling it holds 42gramm seed 3/4 submerged in water. If your seed is heavier, scale floater in Z axis.