Composting on a Grand Scale

See the pile of compost in the image at left? That pile represents all of the food waste from St. Olaf College from a year. Amazing.

I was one of a dozen or so University of Minnesota-Extension Master Gardeners from Rice County who had a chance to tour St. Olaf’s composting facility, its student farm, and its food-service operations last week. We were led by St. Olaf Facilities Director Pete Sandberg and Peter Abrahamson, general manager of the food service and former executive chef at the college.

With about 2,650 students plus faculty, staff and visitors (St. Olaf has a well-deserved reputation as one of the best places in Northfield to eat), the school serves about 32,000 meals a week and generates 700 pounds a day of food waste, including meat, dairy, napkins and other compostibles.  The system that St. Olaf uses to take leftover pizza, hamburger buns and banana peels and turn them into garden gold is efficient, high tech and helps the college in its efforts to reduce its impact on the environment.

OK, not the prettiest picture ever put on this blog, but this is what the food waste looks like as it goes to the composter.

When students return their trays to the college dishwashing area, all the compostibles are collected and ground to a pulp. The liquid is taken out of the waste and every day St. Olaf facilities workers take the pulp out to the compost facility, which is located on St. Olaf land near the Northfield Hospital.

As Pete Sandberg unlocks the door, Peter Abrahamson explains the food to compost cycle. That pile of wood chips provides dry, brown matter to compost with the food waste.

At the facility, the food waste (a green for composting purposes) is mixed with wood chips (a brown), and over the course of 14 to 21 days, it moves slowly through a large composting machine. The interior of the composting facility has what Sandberg called “a barn smell,” but other than that the process is relatively odor-free.

Not quite done. Pete Sandberg shows the Master Gardeners the inside of the composting machine.

After its time in the composter, the mostly finished compost is moved outside to piles. It’s still very hot inside and the composting process continues in these piles, where the compost will sit for several months to a year as it finishes cooking. The facilities workers turn the compost regularly using backhoes to keep the piles going.

Once it is finished cooking, the compost is used all over St. Olaf’s campus — in the flower beds and containers, as well as on the St. Olaf student farm, STOGROW. Bon Apetit, the food services provider at the college, buys all of the vegetables produced at the student farm and uses them in meals during the growing season.

Tomato seedlings at the STGROW farm.

St. Olaf has received national attention for its efforts to reduce its impact on the environment. The school’s composting, farming, and food service programs allow it to “close the circle,” as Abrahamson said, using waste from food to grow more food. While these kinds of systems are not available to home gardeners, increasingly institutions are taking composting seriously and finding better ways to make compost on a grand scale.

For more information on St. Olaf’s composting efforts, check out this video that the college’s PR department put together.


Compost Tips from a Pro

While the compost piles here in Minnesota are frozen solid and buried under a couple of feet of snow now, it’s fun to imagine the time when they will begin churning and decomposing and creating delightful humus for the garden. And, after the Master Gardener class on soils and composting, held a week or so ago, I have a better idea of how compost works and how to get compost quicker. University of Minnesota professor Carl Rosen led the class, which covered everything from what soil tests measure to how to improve your soil’s fertility: basically, add compost.

Here are six tips from Rosen on making compost.

  1. The optimum size for a compost pile is 4 feet by 4 feet by 4 feet. At those dimensions, the compost will heat up quicker and decompose faster. That said, compost happens, almost no matter what you do. If your pile is smaller, it will take longer for the leaves, grass clippings, and vegetable waste in the pile to decompose (think years, not months), but it will decompose eventually.
  2. Compost starter is not necessary. Most compost starters provide microbes and nitrogen to get the material you are composting going. While microorganisms and nitrogen are needed for compost to get started, you can add a couple of shovels of garden soil and maybe a handful of fertilizer to get the same benefits at a much lower cost.
  3. Compost piles like shade. While you can make compost anywhere, Rosen likes shady locations because they protect the pile from drying winds and sunlight, which also dries the compost out and slows the process. Another factor to consider in placing compost bins are the bins’ impact on neighbors—compost that stinks (it shouldn’t) or obstructs a neighbor’s view probably isn’t going to make you the most popular person on the block. Consideration is always a virtue.
  4. Add air. Most gardeners know that to make compost you need brown materials (dried leaves, etc.), green materials (plant debris, grass, vegetable peelings), and moisture. But you also need air. You can add air by turning your pile or by adding bulkier items. If you want to add air with bulky materials, Rosen recommends wood chips, which keep air in the pile because of the spaces around the chips. The only disadvantage of wood chips is that you will need to sift your compost through a screen to get them out.
  5. Is it done yet? When your compost pile is finished, it should be about half the original volume of the pile and have an earthy smell. A well-managed compost pile will be ready in 4 to 9 months. A poorly managed pile will take 1 to 3 years, according to Rosen.
  6. Gardens need compost! While not exactly news, it’s important to recognize how many ways compost benefits gardens. To improve fertility and tilth, add 1 to 2 inches to the top of the soil and work it in 6 to 8 inches, if possible. Compost also makes a great mulch — you need 2 to 4 inches to suppress weeds — and it’s a wonderful amendment to potting soil for containers. Make compost 30 percent of the volume of soil in your containers for healthy plantings.

One other note from Rosen: Compost piles in frigid climates (like Minnesota’s) are dormant in winter. Another reason to hope for spring.