We have chosen to focus on growing our food in the soil almost exclusively these days because we have the space for field production and field production is the most effective use of our time and money when done well. However, this summer I took some time to experiment with a scenario that could be a good application for container growing...extra early potatoes.
I have avoided containers for years because of their higher cost and clutter, so why use containers now? The inspiration to grow potatoes in containers started with the desire to make better use of our early season high tunnel space. We used to fill this space with fast growing salad greens in April before planting our heat loving crops here in May, but now that we are growing mostly just for our family instead of for market, we don't have the need for that many greens and we looked to other crops to fill this hole.
There are plenty of other crops that could be started earlier in the high tunnel but almost all of these need long growing periods that interfere with the May plantings of our heat loving crops like tomatoes, melons, and peppers. These are the crops that really benefit from our high tunnel growing environment so their schedule takes priority in this territory. Therefore, we don't just need a crop that can start earlier in the tunnel. We need a crop that can start early AND be removed when it's time to plant the heat loving crops. Nothing in our family's crop repertoire really fit that bill...unless we could somehow move the crop while it was growing.
That's when containers entered the scene as a possible solution. If we start a crop in containers in the tunnel, we could move them out to a field bed when we need the tunnel space for another crop.
I started to imagine using containers to solve this problem and potatoes rose to the top of a short list of crops pretty quickly as a suitable match for this scenario. Potatoes were a great fit because we would love to have an earlier crop of fresh potatoes in the summer, they can be planted in the cool conditions that the tunnel offers in April, and the isolated growing containers could help us break free from the pressure of soil borne potato problems like scab. I had seen others share their experience with growing potatoes in containers, and while their results were quite vague, they were at least promising enough for me to invest a bit of time and money in doing a trial of our own to get some answers. I was sold on the idea.
The added warmth of the tunnel makes potato planting feasible about a month earlier than our earliest field plantings, which typically happen the first week of May. Therefore, I hatched a plan to plant two trial beds of potatoes in containers in April and would grow them as long as possible in our high tunnel before moving them out to the field to finish their season. What follows is a detailed account of this container growing trial.
Materials
Containers
We used two container types, both 10 gallons in volume, and matched their physical dimensions the best we could. Most fabric containers that claimed to be 10 gallons in size were much shorter than our 10 gallon plastic pots, but I did a little jump for joy when I finally found a source for 10 gallon fabric pots that matched the dimensions of our plastic pots. Both types of containers had a diameter of 15 inches and a height of 15 inches. We bought our plastic containers from Early's Garden Centre in Saskatoon and ordered our fabric pots from this source.
Potting Mix
Our growing medium was essentially a scaled up version of our soil block mix. The recipe we used to make our mix was as follows:
10 gallons of Compost screened through 1/2 inch hardware cloth
10 gallons of Sunshine #4 Mix which is 2/3 peat moss and 1/3 perlite
2 cups of Gaia 4-4-4 Fertlizer blend
Irrigation Equipment
Each row of containers was served by one 1/2 inch line of poly pipe. This poly pipe could be installed into the regular drip line valves that I have at the end of each of our standard beds the drip tape we usually use. Out of this poly pipe came several independent lines of 1/4 inch tubing to bring water to each container. The water was dripped onto the top of each container through a loop of 1/4 inch drip line with 4 emitters per container.
Growing
Planting
Planting took place on April 9 for the plastic containers and April 21 for the fabric containers due to a delay in sourcing the containers. We wanted to compare our data to the records we have from many years of growing field potatoes so we made an effort to match a couple of the variables with that of our field grown potatoes. With 12 inch spacing between our field grown potatoes, we end up with 20 seed potatoes in each of our standard beds, so we also planted 20 seed potatoes in each of our two beds of our container grown potatoes. We planted 2 seed potatoes in each container so we needed 10 containers to match the number of seed we would use for a standard field bed. Then we spaced out those 10 containers along the length of one of our standard 20 foot long beds.
Containers were filled 1/3 of the way with potting mix before depositing two seed potatoes on opposite sides of the containers and adding more potting mix up until the containers were 2/3 full.
Growing
Irrigation was done by hand initially because freezing weather outside of the high tunnel prevented the use of our irrigation lines. Very little moisture was needed in the first few weeks though. As soon as temperatures warmed enough, the drip lines were installed so that the containers could be watered automatically along with all of our other garden beds.
Once the potato stems passed the tops of the containers the final 1/3 of potting mix was added. This ensured that none of the forming tubers were exposed to the sunlight.
Harvesting
The harvest was completed on August 19. It was tempting to harvest the containers early because we could have enjoyed the earliest homegrown potatoes ever, but doing so would have sacrificed a lot of the yield, so we waited. The harvest was only completed after the vines had completely died back.
I share video clips of the harvest and talk through the results in the first part of our our homestead garden tour selections this month. Click the video below to watch or read on for the written results.
Results
Data
The harvest from each individual container was measured and recorded. The tables below show the number of tubers and total mass of every container in the trial.
Analysis
I have shared a graph below of the total harvested mass from each of the container and potato types for a quick visual comparison. I was glad that I tested 2 different varieties because now we can see that the plastic containers resulted in a 25% better yield for both varieties on average. The Bellanita potatoes yielded 33% higher in the plastic containers as compared to the fabric containers, while the Norland potatoes yielded 17% higher in the plastic containers as compared to those planted in fabric containers. We obviously can't conclude that all varieties would perform better in plastic pots, but this does seem like the start of a definite trend.
You may also be wondering how the performance of these containers stacks up against field beds, so the next few graphs also include data from our no dig potato trial last season where we compared the performance of double dig, no dig, and no till beds with two varieties of potatoes. You can see that full study here.
Sources of Error
I will be the first to admit that this trial was far from perfect. The goal was to create good enough growing conditions to test the viability of container grown potatoes while also getting a rough idea of performance differences between container types and potato varieties. Here are a few sources of error worth noting.
The size of a potato seed influences the final yield, and I didn't measure and control the mass of our potato seed for this trial like I did for the no dig potato trial of 2021.
Our sample size was far too small with only 10 containers of each type and only 5 containers to devote to each variety of potato for each container type.
Sun exposure was very close but not perfectly consistent across all of the containers.
Conclusion
The container method proved to be a reasonable alternative to growing potatoes in the soil. While the yields were far from our record harvests in soil over a growing area with the same square footage, changes could be made to the container spacing to further intensify the production. With less space allowed between containers, more containers could be fit into the same space as one of our standard 50 square foot beds, and with just a few more containers in that same space, we might see yields start to surpass that of our field beds.
The quality of harvested tubers was as high as possible. Skin was smooth and blemish free. Only 3 of the 878 potatoes harvested in the whole trial were not marketable. We've had some frustration with potato scab on a few of our plots over the years. Potato varieties differ a little in their susceptibility to scab, but scab is always more prevalent in soil with a low pH because it is caused by a bacteria in the soil that thrives in dry conditions with a low pH. The potting mix we purchased for the containers has a neutral pH so this could have made the difference in getting us a totally scab free crop of Norland and Bellanita potatoes. If you've been troubled by scab as well, containers could be worth considering for this factor alone.
Before we wrap up though, I also have to remind you that production quantity and quality are not the only factors that we need to think about. I have often heard growers say that the appeal of container grown potatoes is that they require less work because they don't need to be dug from the soil. It's true that you don't need to dig them from the soil, but you do need to buy the extra supplies, mix the potting soil, fill the containers, setup an unique irrigation system or hand water the containers, and after all that, you still need to dump out the containers and search for the potatoes at harvest time. There is no question that field grown potatoes require less time from the grower.
The container method also comes with many added expenses. I tallied up all of the purchases for this trial and it gave us a total around $500.
10 x 10 gallon fabric pots - $146
10 x 10 gallon plastic pots - $132
3 x 3.8 cubic foot bales of Sunshine #4 potting mix - $115
40 cups of Gaia 4-4-4 fertilizer - Bag of 10 kg - $55
Drip components ~$50
Homemade compost - Free
I realize these expenses were not all for consumable materials. The fabric pots are expected to last for 5 years, while the plastic pots might last a lifetime. We might also be able to get multiple seasons of use from the potting mix we purchased, but that has yet to be determined. Regardless, when one of our standard 50 square foot field beds only costs me $15 a year in purchased compost, the expense of containers just won't ever compare.
After all this, I can't tell you whether you should or shouldn't use containers in your own situation. All I can say is that container grown potatoes can give you comparable yields to field grown potatoes and that you can probably count on a higher quality of harvest and higher costs. If you have a similar use case to ours, you might be able to justify some of these added costs to take advantage of the early start or portability that container growing can offer.
If you have done controlled trials with container grown potatoes as well, you are welcome to send me a message and share some of your numbers. I would love to compare notes.
