When Joel Karsten was growing up on a farm in Minnesota, he noticed how lushly weeds grew from rotting bales of straw. That made him wonder: If straw worked so well for growing weeds, wouldn't it work just as well for vegetables?
Karsten's question led him to devise a method for growing plants directly in straw bales. His idea is gaining momentum among gardeners with the recent release of his book, Straw Bale Gardens (Cool Springs Press, $19.99).
In Karsten's method, the bale is used as both a container and growing medium. The straw decomposes during the growing season, producing compost that feeds the plants. The twine around the bale holds the straw together and contains what essentially is a small compost pile.
The method reduces disease problems, practically eliminates weeding and gives plants a jump start on those grown with traditional methods, he said. It also puts plants within easy reach of people who have trouble bending or kneeling, and it does so more cheaply than creating raised beds.
Karsten said straw bale gardening is also a good option for gardeners with poor soil — or no soil, for that matter. Straw bales even may be used to grow gardens on hard surfaces such as parking lots, he notes in his book.
And at the end of the season, the bales can go into the compost pile.
Karsten developed his method when he bought his first house and discovered the soil was mostly fill dirt poorly suited for gardening. He remembered those discarded straw bales on the farm, left behind when they would fall off the bale rack on the way to the barn. They were useless once they got wet, so they were ignored. Airborne thistle seeds would take hold in those decomposing bales and grow into tall, healthy plants. He figured vegetable plants would thrive, too.
A horticultural science graduate, Karsten ran his idea past some of his former professors at the University of Minnesota, with little encouragement. It was his father who suggested he give it a try.
"I discovered very quickly that it worked," Karsten said. "It worked very well."
Condition the bale
Part of the success of straw bale gardening lies in a process Karsten calls conditioning the bales. His soil science classes had taught him that bacteria need nitrogen and water to start the composting process, so he developed a method of preparing the bales so the straw would start to break down before planting time.
He starts with common bales of straw, about 2 feet by 1½ feet by 3½ feet, an agricultural leftover that's used mainly for animal bedding and mulch.
Some people confuse straw with hay, but they're different. Straw is the dead stems of cereal grains, left behind after threshing. Hay is a crop grown for animal feed.
Karsten places the bales so the cut end of the straw faces up and the twine is around the sides, not on the top and bottom surfaces. Then, starting a couple of weeks before planting time, he follows a regimen of watering the bales daily and sprinkling them with fertilizer on specific days and in prescribed amounts.
The conditioning system starts the composting process enough that nutrients can be made available to the plants. Heat is produced as the straw decomposes, so transplants and seeds planted in the bales have a warm environment for root development.
That warmth helps the plants take off faster than plants in the ground, he said. And faster growth early in the season can bring earlier harvests.
How to plant in bales
Planting in bales isn't too different from planting in the ground. For transplants, Karsten opens up a hole in the straw, adds the plant and fills in the extra space with a little sterile potting mix. For seeds, he covers the top of the bale with a layer of potting mix and plants the seeds according to the packet directions.
As the plants grow, the straw continues to break down and supply the plants with nutrients.
"In a straw bale garden, we're creating our own 'soil,' quote-unquote, in the bale," he said. Unlike soil in the ground, though, the growing medium contains no weed seeds or disease-causing agents.
That doesn't mean straw bale gardens are immune to weeds, insects and diseases, but Karsten contends his method significantly reduces those problems and makes them easier to deal with.
The bales do need regular watering, but Karsten recommends using a soaker hose and a timer to make watering automatic.
He said the decaying straw provides almost all the nutrients the plants need, although some plants might need more calcium from a source such as crushed eggshells. He also recommends applying a liquid fertilizer every few weeks, either a chemical fertilizer or an organic one such as fish emulsion or kelp emulsion.
Most garden plants can be grown in straw bales, Karsten said, but some are better suited than others. Corn, for example, requires too much space and produces too few ears per stalk to make it worthwhile. He also recommends avoiding perennial vegetables such as asparagus, artichokes and rhubarb because the straw bales are typically used for only one season.
It's good for seniors
Alexandria Straight, an extension agency with West Virginia University who wrote a fact sheet on straw bale gardening, said the method has few drawbacks, other than the bales' tendency to dry out quickly if they're not watered regularly.
It's also important to condition the bales properly and to time planting correctly, she said. An initial spike of heat is produced by the conditioning process, and it needs to subside a bit so the plants can survive, she said.
Straight especially likes the method for people with limited mobility. One of the master gardeners she works with has bad knees, she said, and the gardener was able to take a chair to the garden and work from while seated.
Karsten tells of a woman in her 80s who wrote to him, saying she had given up on gardening because she couldn't handle the physical labor. But then she tried straw bale gardening and told him she grew the best tomatoes of her life.
"You've made one old lady really happy," she told him.
One old lady made him really happy, too.
Read more about Karsten's method of straw bale gardening at Strawbalegardens.com or Karsten's Facebook page, Facebook.com/learntogrowastrawbalegarden.