News from the Edible Demo Garden

December 2023: Caring for the Soil

After the fall harvest was over, it was time to clean up and replenish the soil in the Edible Demo Garden. Healthy soil is fundamental to the success of the next season’s crops. Even in beds that are temporarily fallow, the soil needs to be nurtured and protected. In November, volunteers were busy with three major soil-boosting activities - spreading compost, adding mulch, and planting cover crops.

Why add compost?

The value of compost cannot be overestimated. Most edible crops are heavy feeders and leave the soil depleted of nitrogen and other essential nutrients after they are harvested. Adding a layer of compost to the soil is an earth-friendly way to help restore those nutrients and support good soil structure. Since compost is decomposing organic matter, it needs time to make the nutrients available to plants. In the Edible Demo Garden, compost is applied to all the garden beds prior to planting the next season’s crop.

What is the purpose of mulch?

Mulch is any material placed on the soil to protect it by conserving moisture, moderating temperature, and preventing erosion. Mulch is also used to suppress weeds. Mulch material can be organic or inorganic. Only recycled organic mulch is used in the Edible Demo Garden. Unlike compost, mulch is not intended to amend the soil and the materials used are generally coarser and break down slowly.

In late fall, Edible Demo Garden volunteers take apart the straw bales used to grow warm season vegetables. The used straw becomes recycled mulch. Initially, the straw was considered suitable as compost material, however, subsequent testing found it to be low in nitrogen. Although much nitrogen was added to the bales during the growing season, most of it was either taken up by the plants or washed out by watering and rain.

Why plant cover crops?

Cover crops, sometimes referred to as “green manure”, are another excellent way to protect and improve soil. Cover crops are divided into two main categories: legumes, such as clover and fava beans, and non-legumes, like rye and buckwheat. Legumes have the added benefit of fixing nitrogen by taking it from the air and converting it into a form to be used by plants. Cover crops are turned over when they start to flower and allowed to decompose prior to spring planting.

For several years Edible Demo Garden volunteers have been cultivating a large garden area known as “the back 40”. Planting a cover crop of fava beans in the fall is one of the strategies for improving the poor soil in that area. Before the fava beans could be planted in November, some light tilling of the soil was necessary to improve the penetration and decomposition of the four wheelbarrows full of compost spread by the volunteers. Prior to planting, the bean seeds were soaked in an inoculant containing rhizobacteria to maximize their nitrogen fixation effects.

Paying careful attention to spacing and depth requirements, 150 inoculated fava bean seeds were planted in the back 40 by the volunteers. Some watering will be necessary until the rains begin, but a good crop of green manure should be available to nourish the soil in the spring.

For more information on building healthy soil, click here.