This enchanted sling allows for seeds flung by it to grow both immensely faster and larger than normal. For already magical seeds, for example a Magic Bean, the seed acts as if carefully planted at the point they land. It is still necessary for the landing point to have _some_ planting medium. It would be possible to ‘plant' magic beans into a earth elemental, for example.

Sometimes the sling can be found with magical seeds - such as these, these or these.