I finally got around to digging a bed of sweet potatoes last week. I had told myself that I would dig them before the middle of September but the hot weather of the last couple of weeks had convinced me to wait in the hope I would get a better crop. The last couple of years I have waited until this time of year as well and it is a bit of a risky strategy. I store my sweet potatoes over the winter and use the tubers to propagate the new crop in the spring. Even though the vines were still lush and green when I harvested the tubers, their ability to sprout slips this spring was severely compromised. These heat-loving vegetables are not happy when overnight temperatures drop down below ten centigrade to the extent that it may affect their ability to propagate new plants the following year.
The eight slips that I planted in a raised box in the last week of May spread quickly to cover the whole bed. I used a shovel (having misplaced my spading fork) to dig carefully under the centre of the plant where the tubers grow. As the photos show there was very lush growth this summer resulting in a nice mixture of large and medium sized tubers.
The total harvest from a bed that used about 50 square feet of garden space was about 25 pounds – a harvest that I was very pleased with! The yield depends on many factors – for sweet potatoes the amount of sun and heat we receive is probably the most important. This years harvest compares very favourably with the yield from last summer – a much hotter summer. I figure that plants this year appreciated all the moisture and certainly the raised box helped. By way of comparison the yields of sweet potatoes in 2014 and 2015, which were much cooler, were abysmal.
It has been recommended to me that sweet potatoes should not be eaten right after harvesting them; it is suggested that waiting at least a couple of weeks will allow some of the starches to turn to sugars and the sweet potatoes will be much more tasty. I can certainly attest that the taste of freshly dug sweet potatoes is pretty bland.
Once the tubers are dug they should be cured right away. Curing requires a space that can be maintained at about 30 to 32 C with high humidity for a week. This allows the skin to toughen and slows down the rate at which the tubers will dry out. Tubers can then be stored at temperatures between 13 and 18 C (much warmer than the storage requirements for regular potatoes). A properly cured tuber can be stored for a year or more and can be used to start next year’s crop.
The variety of sweet potato that I grow is called Georgia Jet. The key to successful growing of sweet potatoes locally is choosing a variety that will produce a good crop during our short summer. DO NOT try to grow slips from a tuber purchased from a supermarket. The varieties found there generally require 120 days to produce a crop compared to the 90 or so days of hot weather available to us. Georgia Jet is by far the best variety that I have found for the local climate, having excellent taste and producing many medium and large sized tubers.
Unlike regular potatoes where the tuber is planted in the garden, sweet potatoes are started by planting either shoots (called slips) or vine cuttings in the garden. I have ordered slips from the very helpful folks at the Five-Span Feed Store in Pakenham. Place your order in March for Georgia Jet slips grown by a local market gardener. I have also grown my own slips placing my carefully-stored tubers in water or moist peat moss 4 to 6 weeks before slips are required for the garden. I plant sweet potatoes at the end of May about two feet apart on a raised bed and cover the bed with straw which prevents the vines from rooting at every node (where the leaves join the stem). The objective is a central group of large tubers rather than pencil-thin tubers at every node.
End of Summer?
Remember to keep an eye on the forecast low temperatures and prepare to cover your tomatoes, peppers and eggplant. The cool-weather plants such as kale, Swiss chard, parsley and salad greens will continue happily for a few more weeks.