GROWING COVER CROPS IN RAISED BEDS WITH A SHORT SEASON
After several years of gardening and hearing about how great cover crops are to improve the soil, I finally tried it the past two years. I will NOT be repeating the process this season. Living at 9000′ in the Rockies with cool our springs & autumns and shorter, cooler summers than most gardeners doesn’t make my garden conducive to cover crops. If I wanted to leave a bed two vacant for a good part (or all) of the summer to replenish the soil by cover cropping, I might do it again. But to attempt a cover crop starting early in the fall to grow early in the spring prior to planting summer crops just doesn’t work for me. I have better ways to improve my soil.
WHAT ARE COVER CROPS?
Cover crops are grasses, legumes, and other forbs that are planted for erosion control, improving soil structure, moisture, and nutrient content, increasing beneficial soil biota, suppressing weeds, providing habitat for beneficial predatory insects, facilitating crop pollinators, providing wildlife habitat, and as forage for farm animals. Furthermore, cover crops can provide energy savings both by adding nitrogen to the soil and making more soil nutrients available, thereby reducing the need to apply fertilizer.
Sounds really great, eh? Cover crops are traditionally used in farming applications but can also be used for smaller home gardens. Typically, seed is sown in the fall, from September 1 to October 15. In higher elevations, August 1 to September 15 is said to be optimal. Preferably the seeds should be able to germinate in warmer soil prior to frosts and freezing temperatures. This gives the seed a good chance to be growing and well established, so that when the soil begins to warm in the spring these crops may resume growing. After these crops are allowed to grow, and prior to going to seed, they are tilled into the soil where they compost naturally in the soil, thus providing the improvements listed above.
In my high altitude garden, I have to resort to choice “B”, which for me means to sow the seed sometime in September-October, after beds have been harvested. Seed does not have the opportunity to germinate until spring, but enough growth should theoretically occur to provide some benefit to the soil. Using this method, I have planted cover crops the past two garden seasons (fall of 2017 & 2018). The cover crops did not begin to grow until mid-April to May. Since some of my beds were planted early to mid-May, not much growth occurred prior to the time the covers needed to be tilled in.
Some of my cover crops sown in the fall had barely grown before I needed to till them in to plant my earliest crops. Some beds, saved for later planting, received more cover growth, but in both cases many seeds had not even sprouted prior to tilling. This increased the “weed” population, because for me anything growing in my garden beds that is unwanted is a weed. After tilling in the covers and planting my beds, those dang unsprouted cover seeds kept sprouting up–all summer long, it seemed. They were just weeds to me.
I’d read about Pfeiffer™ Biodynamic Field and Garden Spray, which is to be used “when turning in cover crops to increase soil microorganisms that aid in decomposition and transformation to stable humus.” I used this both of the years I tried cover crops, to aid in faster decomposition because I had such a short amount of time available to till in the crops and get beds planted early enough to mature before the fall frosts. I do not know whether this helped or not as I did not keep any of the beds unsprayed.
I think that in my high altitude, short season climate the cover crops might be helpful for a bed or two that are left unplanted for all or most of the summer, but in general I will not be doing this again. Not many things can be planted after June 15, because the season is so short. This means I’d pretty much have to leave those beds vacant and plan not to plant that year. Also, not many things are harvested prior to August 1, which means I’d have to leave a bed vacant in order to plant that early for optimal cover growth. I can’t afford the space in my 40′ x 40′ garden area of 28″ tall raised beds to leave beds unplanted. As it is, I improve the soil enough and rotate crops around enough I have not experienced problems with my soil. In fact, in my years gardening without the benefit of cover crops, I have had quite good success. I now consider cover crops to be more trouble than they are worth.
To prepare my beds and improve soil annually I have done the following, which works well for our garden. After plants are removed from the beds after harvest they are topped with 3-4″ of compost if I have it, and horse manure if I don’t have the compost. On top of that I mulch well with hay or straw or pine needles (for beds that need a little more acid in the next year’s soil). They sit this way all winter. In the spring the mulch is removed, more compost is added and all is tilled in together. Various organic fertilizers & nutrients are added when planting. I know there is some concern among gardeners about too much tilling, but we like the result after one tilling per year to keep the chunks out of the soil. Beds are then re-mulched for the growing season after seedlings have been planted.
What I may try next year is to place some raw, uncomposted compost materials on the beds that are vacated the earliest, cover them with black plastic and allow the compost materials to cook in the beds while there are still warm days of fall and allow them to remain that way throughout the winter. Hmmmm….good idea!