Increasing Spinach Yields with the Paperpot System

By Christin Mihon, Co-Owner/Farmer of Tasty Acres Farm in Colorado

Getting your crops from seed to sale is a complex process filled with unknowns, uncertainties, and, let’s face it– often uncontrollable variables. But every farmer in the world is bound by a simple truth: you can’t sell what doesn’t sprout. So whether you’re a small market gardener or a large-scale grower, maximizing germination is key to ensuring your farm’s profitability..

On our “almost an acre” urban farm west of downtown Denver, we specialize in lettuces, leafy greens, and baby root vegetables: high-value, high-rotation crops explicitly chosen to maximize profit on our small footprint.

Contending With Mother Nature

Farming here is fraught with challenges. Our field sits at an elevation of 5,564 feet, and our high desert climate is nothing short of extreme. We’ve seen 100+ MPH winds in our first three years, had our crops blanketed with wildfire ash, and experienced 90-degree temperature swings in less than 24 hours. We’re also staring down the ever-increasing threats of climate change every day… so it’s safe to say we spend a lot of our time and energy managing risk. 

Two of the most powerful tools we rely on to do that are a temperature-controlled nursery and the Paperpot system. In the warm and stable environment of the nursery, seeds germinate faster. Grow lights help give seedlings a jump-start. And when it’s time to transplant, my husband Sean and I can complete the job on a 50-foot bed in about half an hour. 

Direct Seeding Spinach

When we first launched our business back in 2019, we imagined we’d be using the nursery and the Paperpot system primarily for Salanova lettuce production. Since then, we’ve learned it’s also ideal for spinach. We’ve decided to share our experience of transitioning to the Paperpot system in the hopes it can help other farmers increase their yields on this crop as well.

Spinach has always been one of our highest-demand crops, one we could sell every week of the year if we had it. In our first couple of years of farming, we didn’t know how much or how long we could expect our spinach beds to produce, so we started experimenting.

We selected the “Space” variety for its advertised year-round growing season and used a Jang seeder equipped with F24 rollers to sow six rows with 1-inch spacing (Front Gear 14, Rear Gear 9). We used the same spacing on all of our 30-inch wide beds year-round.

Comparing Spinach Yields

Our winter harvest spinach, grown inside a high tunnel, proved to be our best-yielding plantings in those first two years, producing about 0.1 lbs/row ft (77-85 lbs from 90-foot beds). 

Our spring field plantings, sown in late April, performed almost as well (about .08 lbs/row ft), but subsequent plantings in May experienced erratic germination and came up well short of expectations (.02-.05 lbs/row foot). Beds planted in June barely germinated at all, and what did sprout ended up bolting before we could harvest a single leaf. Our autumn plantings were slightly better at about 0.06 lbs/row ft., but they still couldn’t compare to our winter harvest rates.

We knew spinach was a cool-season crop, but in USDA Agricultural Zone 6b we were expecting a longer season. Additionally, our lettuce beds, often located right next to our spinach beds, produced well all through the summer. How could a cool-loving crop like lettuce do well while our spinach struggled?

The Unique Requirements for Growing Spinach

After a couple of years of head-scratching, frustration, and research, we gained valuable insight.

First, the UV exposure at our more-than-a-mile-high elevation is 25-30% higher than at sea level and warms the ground much faster in the springtime. Second, we experience more than 300 annual days of sunshine here, increasing soil temperatures even quicker.  

Spinach seeds germinate best at 60-70 degrees. I wish we had the insight to take a soil temperature reading back then. Still, looking back across those first two years of yield data, we’ve determined that our soil temperatures exceeded that ideal germination range much earlier than we realized. Once daylight reaches about 14 hours on our farm, the soil is too warm to germinate the seeds effectively. Since early May through early August is the prime-time growing season, we knew we needed to find a workaround to extend our growing season.

First-Time Growing Spinach in the Paperpot System

In the spring of 2021, we decided to try the Paperpot System for our first spring spinach planting. We seeded 4” chains with 2-3 seeds per cell. After five days in the germination chamber, we started to see sprouts and put them under lights on a 13-hour cycle. We were immediately impressed by the germination rate compared to what we’d seen in the field.  

When we transplanted those seedlings into four rows inside our high tunnel, we were stunned at the consistency and thickness of the stands. It was, without a doubt, the highest-density spinach planting we’d ever had. The rows were so vigorous and thick that it was immediately apparent that this was the right choice. The harvest data confirmed a 15-20% increase in yield over our direct seeded beds. 

The success continued on subsequent spring plantings and opened the door to an additional bonus in the fall. When the soil in the field was still too warm to direct seed the fall spinach, we could start the seeds in the cooler temperature of the nursery and then transplant them out to the field. This strategy allowed us to sneak in a couple of extra plantings that we could never have done with direct seeding.

Key Spinach Production Takeaways

Here are the takeaways that are important for other farmers to keep in mind when it comes to their crops–and not just spinach.

  1. Soil temp matters! Know the ideal germination temperature for your crops, and use a soil thermometer to ensure yours is within range. If not, use the nursery.
  2. Expedite transplants in the nursery- seeds will germinate better in the controlled nursery environment, and longer light cycles can get the seedlings big enough for transplant sooner. 
  3. “Reverse” season extension- when the summer soil is still too warm to germinate cool weather crops like spinach outside, start transplants in the cooler temps of the nursery and then transplant out. Transplants won’t mind the warm soil, and you might be able to squeeze in another planting (or two) before winter sets in.
  4. Seed spinach heavy- whether you’re using nursery trays or direct-seeding, seed spinach at a higher density than we originally did (1-inch seed spacing on 6-rows). Having multiple seeds per cell– or seed drop– will increase density and yield. Johnny’s Selected Seeds sells a “Spinach Seed Roller Pack” that includes Jang rollers that will drop 2-3 seeds simultaneously (instead of a single seed).

Conclusion: Work With Nature

After completing our third year of farming in 2021, we’ve concluded that no matter how hard we try, we’re just not going to be able to grow spinach successfully in the heat of the summer here. It’s now just a winter and shoulder season crop for us. And that’s OK because there’s an exciting new possibility on the horizon this year.

After trialing a few new leafy greens last year, we see real potential in using tatsoi as a spinach substitute in the summertime. It’s more heat tolerant and has been readily accepted by several restaurant clients who use it interchangeably with spinach.  We’ll keep you posted.

In the meantime, we hope you found this article helpful and can benefit from our experience to realize increased yields– and profitability– on your farm. Good luck!


New to the Paperpot System? Check out our free resources all about the paperpot transplanter!

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