What are we doing in the garden right now? A whole lot of stuff, but let's consider the humble potato. We only grow fingerling types for Manresa. They are tastier and more useful for the chef. We can start harvesting them earlier than standard-type potatoes as well.
I buy my seed potatoes from Ronniger's in Colorado. They are certified disease free, and that's important. Potatoes, being in the nightshade family like their cousins tomatoes, peppers and eggplants, are disease-prone. That's one of two reasons why it's not a good idea to take a sprouting spud out of your pantry and plant it in your garden. The other reason is that potatoes purchased for consumption have often times been treated with an anti-sprouting agent. Since you WANT your young potato tubers to sprout, this is not a good quality. I like the price and the selection available from Ronniger's.
When the potatoes arrive, I cut up the larger ones (I know they tell you not to, but hear me out here). When you look at a potato tuber, there are more eyes on one end. Never noticed that before, did ya? Well look at one next time, and you'll see I'm right. So I always cut the tuber such that it's not exactly in half; the end with more eyes doesn't have to be as big as the end with less eyes, get it? I will sometimes cut extra long fingerlings in thirds. Small tubers don't get cut at all.
All the tubers get put in a single layer in seedling trays (open at the bottom for air flow). I then put them in a warm, bright room. The combo of the two gets the potatoes to pop their eyes out (or sprout slightly). This process is called "chitting." No giggles, now. That takes a couple of weeks. Since I put them in an open tray, and give them plenty of air space, the cut ends seal themselves. If I had cut them and planted them immediately, I would run into some rotting issues. That's the reason Ronniger's gives you instructions on not cutting the tubers before planting. I guess they don't trust you to chit them properly.
I like to grow potatoes in 15 gallon pots. That way, I don't have to mess up my planting beds when I harvest them. I can also easily "earth them up" as they grow. Earthing up is essential. As the potato plant sprouts out of the ground and gets bigger, you need to add soil to promote tuber growth under the surface. If you don't do this, then you get less tubers and risk the possibility of the tubers you do have being too close to the surface and photosynthesizing. Green potatoes: bad!
First, we disinfect our stash of used pots with a mixture of one part bleach to 10 parts water. This kills any over-wintering bacteria or viruses on the containers, and is a key step to keep them as disease-free as possible. We also use brand new potting soil. I like Sunland's Premium Grower's Mix. This is sterile and doesn't risk imparting soil-borne bugga-boos into the potato pots. Here's a pot being dunked and twirled in a disinfecting bath:
We then place only 4 inches of potting soil into the bottom of each pot. Lisette, our farm intern from UCSC, is on the job:
Once the soil is in the pots, we simply push five tubers into each one, about two inches under. That means there are two inches of soil below the tubers, and two inches above. The pots are then placed in our large unheated hoophouse and watered well. Although the ambient nighttime low temperatures inside the hoophouse aren't much greater than outside, the potatoes will be happier in there. Since it's late winter, we'll place a heavy frost blanket over the tops of the pots on nights that are forecasted to be frosty, and remove the blanket in the mornings. We'll water them perhaps once a week until they start to break the surface. When the plants reach about 8 inches tall, we'll add 6 or so inches of soil, water again, and let them grow. Another 8 inches or so of growth will trigger another 6 inches of soil added. This will be repeated until the potato plants are quite tall over the top of the container and the soil has reached the rim. They'll continue to need watering every week. When they flower, we can start harvesting. We overturn a few pots every couple of days for the restaurant, dig through the pile of soil, and pull potatoes from the earth that are truly delicious.
These gorgeous Purple Peruvians were photographed freshly pulled last spring here at the farm. Courtesy Chezpim.