Adding Eggshell and Coffee Ground Supplements to Raised Bed Soil. 1.6.22

Now that the last raised bed has its full amount of topsoil, I want to enrich it with available amendments. I generally use compost (garden and kitchen source), coffee grounds, eggshells, wood ash, and leaves. The other raised beds have had all of those added already, either through the year last year or in the fall and winter. This last one, just completed, has only some wood ash at a somewhat deeper level (1 foot deep), and the new supplement of biochar mixed in to the top few inches. 

 My attitude is that not a lot is better than too much. For example, everything is growing well already, so the soil it pretty much OK and we want it to stay that way. Too much of alkaline supplements could result in soil too alkaline for good growth. On the other hand, gardening removes some minerals and the action of time, tilling, bacteria and fungi, degrade soil structure and impede drainage and root growth as the soil is used over the years. Rain also leaches calcium and some other minerals. 

 The most deficient mineral is Calcium. My soil tests always confirm Ca deficiency. Steve Solomon in his books about growing vegetables west of the Cascades, also discussed adding a lime agent, especially dolomite lime that also contains magnesium. Either wood ashes or lime will correct soil acidity in the right amounts, and add lime. Wood ashes also add other minerals, especially potassium (Mostly Ca,then K, then Mg, P, S, Fe and Na). Source. Source. UC Davis recommends not more than 5# per 100 sq feet. I use under 1 pound per 4 x 8 foot bed (32 sq feet). 

 The internet is an excellent source for myth and unsupported non-info, and the idea of adding eggshell to garden is a good example. lots of sites claim eggshells will deter slugs (in my experience, they don't), keep deer away (nope), increase soil calcium or dont (they do). They usually miss that along with eggshell there is the membrane, a source of some nitrogen and some sulfur. A lot depends on preparation and how much and other factors. The best research that I've found so far comes from Iowa, which is a farming state and has massive egg production, resulting in massive amounts of eggshells? There, farmers do plow eggshells into their soil, and corrected for calcium carbinate content, they work as well as agricultural lime. source.   There is also some research on eggshell as a detoxifier of heavy metals in soils.  Apparently, the metals bind to the eggshell and become unavailable for plants to take up and leave traces of in food.  I'm not really concerned about that, but the eggshell is porous, and may be a site for ion exchange for other minerals, and a place for soil microbes to proliferate and do their thing, which I think is probably good.

All that considered, I save eggshells and let them dry out. I usually crush the dried eggshells by hand, but lately I use the food processor to grind them more finely. I let coffee grounds dry out too, for easier handling. I'll look for more about them later, but basically I add them as a nitrogen source, secondarily as a potassium source, and a matrix for soil bacteria, fungi, and food for earthworms. 

 I added about a pound of ground eggshells, and 2 pounds of semi-wet coffee grounds. That's all until time for planting in two months. I'll rake them in when it's not raining. There is no hurry, this bed wont be planted with anything for two more months.