Blossom-end rot: a tomato grower’s worst nightmare. The fact that it’s a common nightmare doesn’t make it any easier to bear. You wait with anticipation as your tomatoes grow from the size of marbles to golf balls to baseballs, and turn from pale green to pink to red. You go to pick them for that night’s dinner, only to find: big, black soggy bruises on the bottom of each fruit.

Yuck.

Sadly, we’ve got a bad case of blossom-end rot in our high tunnel tomatoes right now. The good news is we know the likely culprit: calcium deficiency. The bad news is there isn’t a quick off-the-shelf fix, no easy way to inject our tomatoes with the calcium they need.

Our soil has always tested quite high in calcium. The problem, I discovered after doing some research, is that there are many, many factors that play into whether or not calcium present in the soil is actually available to the plant. It could be not enough moisture. Too high a pH. Too cold a soil (clearly not our problem at this point!). And also this: an excess of certain other nutrients, including magnesium and potassium.

Calcium, magnesium, and potassium all occur in the soil as positively charged ions (cations) that cling to negatively charged sites in the soil. These negatively charged sites are found in high numbers on clay particles (of which we have very few in our native sandy loam soils)—and also on humic acid, that is, on broken-down organic matter. The different cations bully each other to get to these negatively charged sites. In the final count, it’s not the amount of each of these minerals in the soil that matters, but their amounts relative to each other. Judging from our soil tests, an excess of potassium ions are hogging too many of the key sites where calcium needs to be.

A little more research, a few more calculations, and I came up with a recipe for amending the soil. A few bags of the inexpensive rock powders gypsum and dolomitic limestone would add enough calcium and magnesium to rebalance the potassium, while not raising the pH excessively high as regular lime would. I’m not sure whether these additions to the soil will help any this year, but at least I feel like we’re on the right track. We’ll test the soil again and amend the whole field as necessary before next year’s growing season.

If there is any silver lining to this blossom-end rot drama, it would be that it made me rethink the fundamentals of organic farming. I was reminded of this when I called a soil consultant I know, Carl Rosito, to check the proportions in my proposed “recipe.” Carl approved the recipe, but emphatically reminded me that I had to figure out how to address, in a holistic way, the organic life of the soil.

Like food, soil is more than just a conglomeration of nutrients. When we count only the major, easily-seen components of soil, we miss the complex system of interactions within the soil, and between the soil and the plant. Healthy soil is not inert matter, but a complex web of life. The life in the soil web is comprised not only of decomposed organic matter (providing the humic acid which holds onto nutrients such as calcium and makes them available to the plant), but also of living beings, from earthworms and nematodes to fungi and bacteria. Some of these are pathogenic but many more of them are absolutely essential to the cycling of nutrients. Only with their help are inert nutrients such as calcium converted into a soluble form that plants can use. It isn’t that there is a deficiency of some one nutrient or another in the soil in our high tunnel, it’s that there is a fundamental dysfunction in the soil processes.

We can’t pretend to fully understand how nutrition works, either in human bodies or in plants. There is complexity there—mystery and miracle if you will. What can we do in the face of such mystery?

When it comes to human nutrition, the advice is to eat a wide variety of whole, unprocessed foods, mostly from plant sources; to hearken back to traditional diets to find wisdom. In the case of soil nutrition, the “traditional diet” is lots and lots of organic matter. In other words, compost. Compost may be low in nutrients by the standards of chemical fertilizers, but what it lacks in nutrients it makes up for in living energy. All that living energy is what wakes up the soil, freeing up the nutrients that are already there. Carl urged me to track down whatever sources of vegetative material I cold find—wood chips, grass clippings, leaves—and start getting more serious about making compost, even if all we did was leave big piles to sit until they broke down over the course of two or three years.

It’s certainly easier to open a bag of fertilizer, organic or chemical. But my blossom-end rot take-home lesson is that if we are going to sustain abundant vegetable crops year after year, we have to recommit ourselves to sustaining the life of the soil. This means firing up the dump truck and the front-end loader and getting serious about making piles.

So that’s our work ahead: lots of compost. Piles of great decomposition, all cooking down in the name of better beefsteaks. Stop by the high-tunnel next year to inspect the results! | Rachel Evans has grown vegetables at the Sunshine Farm since 2006.We trucked 30 tons of hot and steamy mint compost onto the farm this year. It can take 8 to 10 tons of compost per acre per year to maintain organic matter in garden soils. Because of the shortage of animal farms nearby, sourcing high quality compost, or raw materials for compost, is a challenge for us. In the past, we’ve trucked composted chicken manure over from the west side and have most recently been using compost made in Royal City from mint wastes. Unfortunately, this mint compost is extremely high in potassium—just what we don’t need! The compost question is one we’ll continue to sort out in future years.

We trucked 30 tons of hot and steamy mint compost onto the farm this year. It can take 8 to 10 tons of compost per acre per year to maintain organic matter in garden soils. Because of the shortage of animal farms nearby, sourcing high quality compost, or raw materials for compost, is a challenge for us. In the past, we’ve trucked composted chicken manure over from the west side and have most recently been using compost made in Royal City from mint wastes. Unfortunately, this mint compost is extremely high in potassium—just what we don’t need! The compost question is one we’ll continue to sort out in future years.

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