Gordon Johnson, Extension Vegetable & Fruit Specialist; firstname.lastname@example.org
Sweet potatoes for processing are being grown on Delmarva in larger acreages. These are dug using a modified potato digger, conveyed to trucks, and then are transported to the processing plant.
In contrast, there are a considerable number of small acreage commercial growers of sweet potatoes on Delmarva because it is a profitable crop for fall sales, especially before the holidays. The following are some guidelines for harvesting, curing, and storage of sweet potatoes for local fresh markets:
Sweet potatoes may be dug any time they have developed market size. Normally, vines will have started to yellow at this time.
Caution must be taken when digging sweet potatoes. The sweet potato has a thin, delicate skin that is easily broken. Any cuts, bruises, or skin abrasions will reduce quality and storability significantly.
A common method for digging is using a one bottom plow or middlebuster to expose the row. Sweet potatoes are picked up by hand and then placed into baskets, slatted crates, or small bins, being careful not to cause cuts, abrasions, or bruises. Small acreage growers can also lift potatoes using a garden fork. Expect to miss about 20% of marketable roots with these methods.
Modified potato diggers can also be used for harvesting. The key with these mechanical diggers is to carry enough soil up the separation chain to limit root contact with the rods and to have a limited drop to the ground to reduce cuts and bruises. Vines normally are mowed before digging. Again, sweet potatoes are picked up by hand into baskets or bins. Larger machines that convey the sweet potatoes to a grading line or bins are used on some farms in major sweet potato producing areas such as North Carolina.
Sweet potatoes are best dug while soil temperatures are relatively high and soil is on the dry side. Roots are injured below 55°F. If sweet potato vines are exposed to a light frost, usually no injury will occur if roots are dug quickly because soil temperatures have not dropped too low (it should still be around 60°F near most roots). Heavy frosts or freezes will drop soil temperatures below critical levels, causing significant losses.
Washed and graded sweet potatoes can be sold immediately without curing; however, for Thanksgiving and Christmas markets, curing will be necessary.
Bins or baskets containing harvested sweet potato roots should be taken to an area to cure. Do not wash before curing. In the curing process, cuts and abrasions are healed over, allowing for longer term storage. The ideal conditions for curing are a temperature of 85°F and 90% humidity for 5-7 days. This is an issue because most growers in Delaware do not have dedicated curing houses. As an alternative, place covered baskets or bins containing sweet potatoes in an empty greenhouse. Water the floor heavily or put pans of water out to keep the humidity up and turn the heat on so night temperatures do not drop below 70°F. Set fans for 85°F for the daytime. Using this method, curing will take 14 days usually.
Once cured, store as close to 60°F as possible, but no lower, in an area where you can maintain a high humidity. Most local commercially grown sweet potatoes are stored no longer than Christmas.
Before marketing, cured sweet potatoes should be washed and graded, allowed to dry, and then boxed.