do you want the plant for décor purposes? if yes, use second spring to keep it looking young forever without having to tend it (I do this on my decorated houses). you can always harvest it at anytime either way. It won't leave until you tell it to
Does anyone know how long you have to harvest an Elder plant? Or if it just stays Elder until you do eventually harvest it.
It will remain at Elder until you decide to harvest it. Most players who garden for Mega Snacks or specific Reagents let the sit until Double Garden Rewards. Double Rewards will give you Double Garden XP and snacks and reagents as well and double seeds from plants that seed themselves. Some plants don't reseed.
Double Garden Rewards should be sometime in May but not guaranteed.
Does anyone know how long you have to harvest an Elder plant? Or if it just stays Elder until you do eventually harvest it.
When a plant is at it's Elder stage, it doesn't develop any needs or attract any pests, and will never die. You can leave an Elder plant there for as long as you like until you decide to harvest it! When you do decide to harvest it, you will receive much greater rewards than the rewards harvested from a Mature plant. Unfortunately, once you harvest it, the Elder plant will disappear forever and can't be revived.