NPK: Feed soil and plants — not the deer
In a hot summer, when the biggest garden project to come to fruition would be the completion of writing and photographing for a new book, 34 years of feeding my soil has rewarded me. As soon as I enter the garden gate I am nourished, long before any of the edibles satisfy my hunger.
With the expected mid-October frost nowhere in sight, I may have a few more weeks of this inspiring fecundity. Cardinal flowers greet me just inside the gate, scarlet trumpets on a vigorous annual vine, tempting the hummingbirds in the early morning. Tomatoes reach well over eight feet, loaded with fruit.
At the south end of the tomato bed, lablab beans are full of fruit, shiny purple pods that glisten in the sun. A few sprays are picked to accompany the large red zinnias I’ll cut on my way back to the house.
Heading for the raspberry patch where the earlier heat spells damaged some fruit, I am now rewarded with large succulent berries. Before I start picking I pause at the blue morning glory tumbling over the arch at the end of the raspberry patch, its huge flowers an echo of the Sierra sky. Small native bees are already at work in the morning glory and raspberry blossoms.
My focus for weeks has been on writing. I do not have time to think about fertilizing plants. Soil preparation is the key to my success, as it is every summer.
There are no bad years for gardening, only challenges to overcome: heat, quail, raccoons, deer (remembering to close the gates!), occasional bears, and this year, harlequin beetles.
Vegetables differ in their requirements. Leafy vegetables need more organic nitrogen (N). Edible crops grown for their root (garlic, onions, carrots, radishes, potatoes, turnips) or their fruit (tomatoes, beans, eggplant, peppers, squash) must have adequate natural phosphorus (P). Phosphorus is essential for roots and flowers, so all plants need it, and it is not naturally occurring in our native foothill soils.
Potassium (K) is plentiful in Sierra soil, but if you are trying to garden in raised beds without soil, it may need to be added in the form of greensand. This is an essential nutrient for cell division and health of any plant. The soil pH refers to acidity and alkalinity. Foothill soils are in the acid range (5.0-6.0) in almost every location. Nutrients are absorbed by plants within a very specific pH range. For phosphorus it is narrow, primarily 6.5 to 7.5. The addition of oyster shell will raise the pH and increase availability of other nutrients.
A good gardener prepares soil to meet individualized requirements. This is where an understanding of NPK and pH is helpful.
Beginning with adding a good compost and rock powders, vegetables (and other plants) utilize the nutrients and minerals available in our foothill clay soil. I have seen successful gardens this year grown only with the addition of “Carolyn’s Mix” from Rare Earth, a blend of mushroom compost and rice hulls, with phosphorus plus oyster shell. “Carolyn’s Mix Plus” adds one part chicken manure to two parts of the basic mix, and will increase the soil microbial activity, especially important where edible crops are grown.
Phosphorus is not water-soluble and must be added into the soil profile in the root zone, 15 to 20 pounds per hundred square feet. Oyster shell should be added at the same time, five pounds per 100 square feet, but may be added on top of the soil. Rains or irrigation will move it through the root zone.
Nitrogen may be added anytime, and is the easiest to overdo. Too much nitrogen and tomatoes have lush leafy growth at the expense of fruit. Carrots fork in soil high in nitrogen, and may have leafy tops with no edible root. The solution? Add the compost in the fall and grow a cover crop. Or at least order your material well in advance of spring planting. Let your soil mellow.
Feeding the deer your flowers and shrubs? Consider reducing the nitrogen you add. Deer browse on plants brought in from a nursery, eating even those considered “deer-resistant” because they have usually been fed with nitrogen.
I have a deer path through a large planting of Lamiastrum, the groundcover untouched. However, a flat of Lamiastrum recently held for a landscape client (and surely under the influence of nitrogen to induce leafy growth) was an immediate target, placed just a few feet from my large planting. Protect all plants when they are purchased or first planted!
Carolyn Singer has gardened organically in the foothills since 1977. She will teach a class on water-efficient and deer-resistant landscaping (including ornamental grasses) at Peaceful Valley Farm & Garden Supply from 9:30-11:30 Nov. 3. Learn more at http://www.carolynsingergardens.com.
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