Gardening in straw or hay bales has become popular. Growing a garden in bales allows gardening when conditions do not allow working the ground, when there are poor soil conditions or when the gardener may have limited ability to move in or around the garden.
Other benefits include extending the growing season by planting a little earlier in the spring and later into the fall as the bale provides insulation to plant roots. Plus, as it decomposes, it provides heat to keep plants warm.
Another advantage is plants are growing above the ground, so they remain cleaner and there is a reduced chance of ground-dwelling insect and disease attacks. Straw or hay bales from alfalfa, wheat, oats, rye or other cereals are suitable for making such a bed. Straw bales are preferable over hay since straw contains less seed than hay.
The straw or hay bale should be tight and held together with two to three strands of twine, preferably made from a biodegradable material such as sisal, but synthetic materials can also be used. Biodegradable twines should be positioned parallel to the ground to avoid their hastened decomposition.
Fresh straw bales must be watered and allowed to decompose for at least one to two weeks before planting. This is important because the microbes in the bale will use any nutrients present to breakdown (or decompose) the straw, depriving the plants of nutrients such as nitrogen, phosphorus and other essential elements.
Decomposition is an exothermic process; this means substantial heat is released as the fresh straw is broken down. This can further damage seed or seedlings placed directly into a fresh bale. Thus, old or pre-seasoned bales are desirable for bale gardening.
There is a method of speeding up this seasoning of new bales in situations where a gardener may need to hasten planting. Applying a nitrogen-rich fertilizer to the bales, then watering it in thoroughly, will accelerate this decomposition process. This can be repeated at regular intervals until a substantial temperature change (or spike) is no longer detected several inches into the bale.
There are two ways to plant the “bed.” One way is to make pockets or holes about 3 to 4 inches deep by gently loosening and carefully removing a small amount of the straw. The number of pockets can vary, depending on what the grower plans to grow. The other method is adding or spreading soil materials on the top of each bale, also called a flat straw/hay bale bed. For both methods, the growing medium can be a compost or manure. Once the growing medium is in place, the bales need to be moistened. It is important to induce a good rooting environment for successful production on bale beds.
• Watering: Proper watering is crucial because the water infiltration rate is high in straw bales, and they can dry out quicker. The best way to approach watering is through a drip or soaker hose system set up on a timer.
• Fertilization: The nutrient supply for plants established in straw bales is also critical. Growers must ensure that an adequate supply of the major nutrients is available. Nitrogen deficiency is common. If crops show yellowing of old leaves, it may be an indication of nitrogen deficiency. Purpling is a symptom of phosphorus deficiency. Leaf margin necrosis is a symptom of potassium deficiency. Straw bale beds can be enriched with the application of soil, manure, compost or a mixture of these.
• Weed control: The greatest benefit of the straw bale garden is there are, in general, fewer weed problems. Weeds that do show up can easily be removed mechanically or manually.
For more information on straw bale gardening, see the OSU Extension fact sheet PSS-2264 “Straw Bale Bed: A Way to Garden While Building Soil.”