I know this is lazy but.... While I am not an experienced in game gardener (I normally only grow orange petals) how about an option that if you place a beehive in the general area of the garden beds the bees will self pollinate the plants. This option could just be something that its turned on/off via the beehive. You could also maybe add an option the bees would randomly pollinate the plants with pollen from the surrounding area but that sounds like a coding nightmare. Just the self pollinate would make sense