June, you are a serious garden season sweet spot. Veteran spring crops are side by side with freshly planted warm weather selections, both eagerly lapping up the ever more present sun. Hopefully you were among the visionary vegetable veterans who were watching their soil temperatures and forecasts, those who waited and planted their tomatoes and peppers after the May 17 snow flurry. Many a gardener is on round two of planting after losing these delicate plants to a late frost!
Remember, if you engage in risky behavior, make sure to use protection; cold frames, low tunnels, and cloches (Wall-o-Waters). They are key to making sure you don’t lose precious plants to dips in springtime temperatures. Monitoring soil temperature is the best way to know the optimum time to plant, as most of our vegetable plants are more sensitive to soil temperature than air temperature, and the soil is slower to heat and cool than air. Like the flywheel on an engine, the slow and steady temperature of the soil is a more accurate indicator of season than whether you are wearing a t-shirt or a coat. The wild weather roller coaster we’ve experienced thus far in 2017 is a clear reminder of the age of climate chaos we have moved into, and a reminder to be designing your own personal food system to be increasingly resilient.
Now that the plants are in, you can relax, intoxicated by visions of impending abundance. If your tender little veggies have their roots embraced by luscious, nutrient rich soil, they’ll blast off in the astounding seasonal growth annual plants perform. In a race against the frost clock to complete their life cycles, nothing can stand in their way—if they have the resources they need to grow. But sometimes we’ll see that sprint interrupted, identified by slow growth, purple tinged leaf tips or chlorosis (yellowing of the leaves). At this point, one must make a quick assessment of the nutrient deficiency at hand, and act to correct it.
But exactly which nutrient is the plant not acquiring? Yellowing leaves are caused by a lack of nitrogen, but also of iron, sulfer, copper, and molybdenum. How to narrow it down?
Nutrient mobility
Then I came upon a unique way of observing the way plants use nutrients. The game changer is the concept of nutrient mobility.
Depending on the way an element behaves chemically, once a nutrient is assimilated into the plant, it can either be shuffled to another location within the plant, or not. Take nitrogen, for example: When the plant experiences a shortage, it will move the nutrient from where it is no longer crucial to an area of more significance. These nutrients are said to be mobile. Deficiencies of mobile nutrients show up in older leaves, as the plant is cannibalizing the elements there and moving them to the more actively growing areas. Some nutrients, once assimilated, are there permanently, and thus are immobile. These deficiencies show up first in new growth, as the plant has an inadequate supply and is unable to relocate the stash it has.
I’ve included two handy lists to aid in identifying nutrient deficiencies when they appear. The first list identifies locations on a plant where deficiencies appear, and what elements are associated with these locations. The second is a list of all the macro and micro nutrients, and a brief description of how the deficiencies appear visually.
Use these two lists together, first identifying which nutrients might be missing based on where you are seeing symptoms, then narrowing it down to a specific nutrient based on visual clues. When in doubt, especially in cases of chlorosis, chances are it is a macro nutrient missing rather than a micro nutrient, as plants use far more of these by volume to attend to their daily chores.
When correcting a nutrient deficiency, remember how plants acquire nutrients in healthy soil in the first place before rushing to buy chemical fertilizers. In healthy soil, microbes are the key to fertility. Plants nurture these microbial communities by feeding them with exudates of starches and sugars produced by photosynthesis, and in turn those communities buffer the pH around the plants’ roots to increase nutrient uptake. In the case of beneficial fungi, they even deliver the needed nutrients to plants from areas outside of the root zone. Earthworm digestion unlocks chemical bonds and makes certain nutrients available to the plant.
The goal of every gardener should be to pamper these microbes, and allow them in turn to pamper the plants. Feed the soil, not the plant.
James Loomis is the Green Team farm manager for Wasatch Community Gardens.
Nutrient deficiencies by plant region
Growing points: calcium, boron
New leaves: sulfur, copper, iron, manganese
Middle leaves: zinc
Older leaves:
nitrogen,
phosphorous, potassium,
magnesium, molybdenum
Nutrient deficiencies by visual indication
Macronutrients
phosphorous: stunted growth, bluish leaves (mobile)
potassium: dead spots (mobile)
Magnesium: interveinal chlorosis (yellow leaves, green veins) (mobile)
calcium: deformed growing tips (immobile)
sulfur: yellowing leaves (immobile)
Micronutrients
Zinc: slow and then no growth, lack of stem elongation, and yellowing (mobile)
Molybdenum: chlorosis, some leaves begin to curl (mobile)
Boron: damage to growing tips, problems with fruit and flower
formation (immobile)
Chlorine: plant tips wilt and turn bronze, often mottled with spots of chlorosis (immobile; excess causes
yellowing of leaf margins)
Copper: chlorosis. curling of leaves, excessive branching (immobile)
Iron: chlorosis, (immobile)
Manganese: interveinal chlorosis (yellow leaves, green veins)
(immobile)
Nickel: leaf tip burns (immobile)