Harvest onions grown from sets when they are 6 to 9 inches tall for immediate table use. Harvest before hard frost. Parsnips are not poisonous if harvested in early spring. This usually requires an additional 2 to 3 weeks. For storage, harvest when full sized with firm skins.
Tubers continue to grow until the vine dies.
For new potatoes, harvest at any early stage of development. Harvest pumpkins when they are fully colored and the skins have hardened enough to resist the fingernail test. Harvest before a killing frost. Established plantings can be harvested for approximately 8 weeks. The quality of the stalks decreases toward the end of the harvest period.