In the spring, I wrote about the Seattle Community Garden’s experiment with growing sweet potatoes. Although I’m not there to find out how it turned out, John sent an email out to the garden group (I’m still on the email list) with the results. I thought I’d share what he sent with you so that you can learn from our experience if you’re trying to grow sweet potatoes in a similar climate.
Although in spring we were planning to plant the sweet potatoes in the in-ground long beds, they decided to plant them in raised beds in the end. I forget the rationale for that decision, but it may have had something to do with soil temperature. I believe these sweet potatoes were planted at the end of June or beginning of July, and the garden group harvested them a little over a week ago, just before Seattle’s first frost.
Of the 15 sweet potato plants planted in those two beds, here are the harvests results:
There are a few giant sweet potatoes in the bed 13 harvest, but overall, this isn’t all that impressive.
John says: “the soil in these two raised beds was ‘not optimal’ to put it mildly… too much nitrogen to grow sweet potatoes (excessive vine growth) and poor soil consistency – ‘gooey wet’ when we planted them….then hard caked, and very difficult to dig in when we harvested.” Sweet potatoes, according to John, prefer sandier soil and need more potassium for root development. Bed 13 did slightly better than bed 14, he postulates, because bed 13 gets a bit more sun. John and Sue had planted some sweet potatoes in their own garden in a sandy, sunny bed and found that their harvest was more consistent and easier to dig up.
John also put a lot of work into curing these sweet potatoes. Apparently, they need to sit for 4 to 14 days in a warm, humid place (85F and 90% humidity) in order to sweeten up, and then they can be stored in a dry cool place (55-60F).
John built an insulated box and used an open crockpot filled with water to create heat and humidity for the space.
Here’s what they looked like after 6 days in the curing box:
Despite the mediocre results this year, it sounds like they are not discouraged and are excited to try again next year. John suggested replacing the soil in two raised beds that get the most sunlight with sandier soil.
There you have it. If you have experience growing sweet potatoes in a northern climate, I’d love to hear about it!