Coffee grounds (UCG), clay and fertility
I have some experiences with coffee grounds and clay that should be shared.
For over a year, I stopped at the local Starbucks and picked up about 3 gallons of used coffee grounds (UCG). Having read the Sunset Magazine analysis of the nutritional values and the recommendations there and on this board, I assumed that it would be good to dump lots of coffee grounds in my vegetable garden beds.
I estimate that I had applied about 5-8 cubic yards (yes, really) to various garden beds, including berry beds and vegetable beds, as well as to the lawn. Two of the vegetable beds got covered with at least two inches.
I subsequently found research that showed that caffeine inhibits root growth in a dose dependent rate.
Here are my observations so far. My soil is alkaline clay, pH of 7.8. I use lots of homemade compost, some agricultural sulfur pellets, and bone meal as soil supplements.
Legumes don't germinate well in soil with lots of raw coffee grounds in them, despite being pre-soaked with vitamin C and inoculated. Peas and beans did not do well despite. Pumpkin, watermelon, and muskmelon likewise did not grow at all.
Corn, tomatoes, peppers, radish and carrot, potatoes all seemed to tolerate the coffee grounds better than the more tender plants. Some sunflower plants were allowed to grow and they reached a height of 12' or so, so they liked the coffee grounds.
This spring, while turning some compost into the vegetable beds, I found that the clay soil had been stained nearly black to a depth of about 6-8". In some places I found many young worms living in the stained soil. The clay soil in my yard gets hard as rock when it is dry, but the stained soil was friable and porous.
I have not added raw UCG to my beds this year. Again, the peas are not germinating well. Corn and potatoes are sprouting well, and the tomatoes and peppers are growing well so far.
I'll have to remember to update this later in the year.