If my soil test shows above optimum organic matter, why is my garden not doing well?

Question:

I received my soil test back recently. I’ve had problems growing lettuce, carrots, kale, cabbage, etc. They start nicely, turn woody, and do not grow. The soil test indicates that there is above optimum organic matter. Why do you think my garden is not growing well? 

Answer:

Jonathan Foster, Home Horticulture Outreach Professional

The good news is that your soil report looks pretty good, both for nutrition and pH. The organic matter is high, but that isn’t necessarily a bad thing as long as it’s breaking down normally into the soil. You probably don’t need to add compost or manure this year, if that’s an annual amendment in your garden. The nitrogen and potassium amendment suggestions are standard for vegetable gardens (nitrogen, in particular, cycles freely through soil, so it isn’t a standard test parameter and it’s addition is kind of a default suggestion unless you are getting out of control leafiness from the plants, a sign that the N is high). It doesn’t sound like that is a problem, so I would apply the full recommended rate for N and potassium, and the alfalfa meal is a good way to get both in one shot.

I suspect the problems with the crops aren’t related to soil nutrient composition, but rather to an environmental factor like insufficient sunlight or inconsistent soil moisture–light and water are the most common limiting factors in plant growth. Your question mentions lettuce, carrots, kale, and cabbage, all of which are fairly tolerant of lower light conditions (meaning at least 4 hours per day of direct sunlight). If they are getting less light than that, that would be my first suspicion for a culprit and would recommend planting them elsewhere or trimming nearby trees/shrubs that might be shading the garden. That said, these crops will all produce something at 4 hours a day, but it won’t be as good as a bed in more direct sunlight.

If you water by hand, I would recommend looking into drip irrigation on a timer, which is way more reliable for keeping the soil moist, but not sodden. You can also try simply watering very consistently and monitoring the moisture, but that’s quite a bit more labor intensive. I also heavily encourage the use of mulch for many reasons, but chief among them is insulating the soil against evaporative water loss, which is a fancy way of saying it also helps keep the soil consistently moist, but not sodden.

The last thing to mention is making sure these plants are being planted when they should–lettuce in particular bolts (i.e., begins to flower and produce seeds) when it grows hot, making it first unpalatably and then inedibly bitter and unpleasant to chew. It’s a cool season crop, so if you’ve been growing it in the hotter months, that could be a contributing factor. Normally, I might also worry about your soil texture being a problem, especially with carrots (who like fluffy, loose soil), but I suspect your texture is good with that much organic matter in it.

Happy gardening.