Preparing for Spring with Cover Crops and Soil Building 2015

Our summer season has officially come to a close. The leaves are continuously transitioning into their winter apparel, issuing forth a profusion of reds, oranges and yellows in the maple understory on the hills surrounding our farm. And although it may seem like a season of rest is upon us, there are still a number of jobs yet to accomplish before retiring the garden until the spring. Maybe you are a fair weather gardener; your season encompasses the warmest months of the year that span from May until September. This abbreviated version of the growing season leaves out some of the most critical times of the year for both building soil and preparing your garden for the next summer. The time that exists between early September and early November is what I typically think of as one of the two shoulder seasons. The fall shoulder season can be a very productive time. It is the season for planting greens, cilantro and spinach. It is the time for preparing beds for over-wintering leeks, carrots or parsnips. It is the time for planting garlic, for mulching unused beds, for pulling the weeds that are going to seed and for putting away irrigation. And although the summer squash and cucumbers may be tiring under the strain of the cooling nights, the summer planted kale, collards, chard and choy are all thriving.   The spring sown Brussels sprouts and celeriac are nearly ready for harvest. And it is when you may be tilling under your summer sown cover crops and sowing your cover crops to overwinter.

So how does one go about using these very limited last days of the growing year to the best of their abilities? How does one prioritize the jobs that are left to be done? Perhaps it is best to begin by mentally jumping forward to the spring. What are your goals for the next season? Improving soil texture? Reducing moisture loss? Hastening your first harvest date? Fewer irrigation repairs? All of these questions can help to pinpoint the goals for fall that will increase your enjoyment of your garden during the coming spring.

For me, soil building has been a long standing priority. After working in many sandy gardens, it became obvious that an increase in soil organic matter should be a goal for every growing season. The most effective way of doing this has been to incorporate a cover crop into the garden at least once a year. Many gardeners working with small spaces find the easiest way to add a cover crop rotation without giving up growing space is to plant the cover at the end of the season (September) and allow it to overwinter. During the winter, the fall planted cover crop protects the soil from nitrogen loss to the atmosphere and soil erosion from wind and rain. In the spring, the crop is allowed to grow until it is at the 50% flowering stage and is then turned under and allowed to decompose. This added organic matter has several functions. The small pieces of decomposed plant material act like sponges, trapping some additional moisture in the soil. This is incredibly important in arid regions where maintaining good soil moisture is critical to healthy plant growth. The added organic matter also loosens clay-rich soils. It opens up pore space which allows air to move through the soil and allows plant roots to grow. If legumes are used as the cover crop (ex. peas, vetches and beans) it can act as a readily available source of nitrogen when incorporated in the spring.

 If cover cropping is not an option, an alternative form of soil building involves fall mulching. Although most people consider baled alfalfa as animal feed, it also makes a rich and effective mulch. We have been using alfalfa as a mulch for our garlic for the last two seasons. There is a noticeable increase in plant vigor in the beds that received the alfalfa mulch vs. straw mulch. After some consideration, the reason for this became blindingly obvious. Straw is strictly a straight carbon source and sequesters nitrogen from the soil as it breaks down. Alfalfa (a legume) when incorporated in the spring, increases rather than decreases the amount of nitrogen available in the soil thereby boosting the production of following crops rather than stealing from it. Weed-free alfalfa can be used to cover dormant beds to protect from wind erosion during the winter months. When spring arrives, it is shoveled into the beds and allowed to decompose just like a cover crop.

The list of fall-related gardening projects is long and involved. It is hard to do it all. However, taking the time to care for your soil is probably the job that will offer the most immediate and satisfying rewards. Have a great winter, and Happy Gardening!