Last fall I decided to experiment with three different cover crops for my raised vegetable beds.  A cover crop serves multiple purposes, including by serving as a “green manure” that replenishes soil as well as provides weed suppression.  I thought it would be a fun experimental project to plant a cover crop even though my raised beds are small and it is relatively easy to add compost and to weed them.  In late fall, I selected common buckwheat (Fagopyrum esculentum), a “soil builder” mix of peas and oats (Pisum sativum and Avena sativa), and fava beans (Vicia faba ‘Windsor') and planted each crop separately in each of the three raised beds.

A cover crop planted in the fall, allowed to grow over the winter, and then turned into the soil can replenish nutrients and improve the soil structure.  For example, legumes add nitrogen, which is a macronutrient primarily responsible for plant growth, to the soil.  In addition, a cover crop can suppress weeds.  Other uses for a cover crop include preventing soil erosion and soil compaction, providing habitat for beneficial insects, and forage for animals.  I was mostly interested in adding nutrients, suppressing weeds, and improving the aesthetics of the raised beds that are typically barren in the winter by filling them with useful green growth.   

In the interest of full disclosure, I made the mistake of planting vegetables in portions of the raised beds that ultimately got in the way of the cover crops.  I had some leftover seeds that I threw into the beds thinking that nothing would come of them.  To my surprise, the vegetables thrived, which made cutting down and incorporating the cover crops nearly impossible.  This meant that I wasn't able to complete the portion of the experiment that involved turning the crops into the soil or using them as mulch.  (Well, I could have, but I preferred to keep the vegetable crop!)

The peas and oats were my least favorite.  The peas are supposed to add nitrogen to the soil while the flowers attract beneficial insects.  The oats are supposed to provide green manure while suppressing weeds.  The peas, however, didn't grow well, which is unusual in my yard since I typically have good success with other types of peas.  The oats looked so much like tall, grassy weeds that we see in vacant lots that I pulled them out early for fear they would spread to the rest of the yard.  It turns out the oats are very good at erosion control too and I pulled up big clumps of soil that was entangled in their roots.  This was a little annoying since I had added soil and compost to the bed and then ended up pulling some out with the plants. 

I thought the buckwheat was interesting, but it didn't grow as well as the other cover crops.  I think it was somewhat shaded out by the vegetables I planted.  The buckwheat is intended to provide green manure and weed suppression.  The plant had pretty heart-shaped green leaves and quickly set small white flowers that are supposed to attract beneficial insects.  Buckwheat is supposed to be turned into the soil before the seeds form, but I couldn't reach over the vegetables to cut them down and instead just pulled the plants out.  I would definitely try this cover crop again.

While all plants did well, the fava beans were my favorite.  The plants filled the raised bed, growing to about 3-4 feet tall, and were sturdy even in the wind.  They had beautiful white and black flowers when little else was blooming in the yard.  Although I should have cut the plants down and turned them into the soil before they set seed, I decided to save them for their bean crop.  In the future, I may split the difference and save some plants for and some for the soil.

Although I didn't complete the experiment by turning the cover crops into the soil, it was still fun to experiment with different types of plants and learn what to try next year!