If you have a soil test done on your unimproved foothill soil, in the area where you fantasize about having a lush and abundant garden, it will very likely indicate both phosphorus and nitrogen shortages.
No surprise. These are predictable deficiencies in Sierra foothill soils.
Phosphorus is the middle number in the analysis of any fertilizer, organic or non-organic. Known as NPK, a ratio that guides you in selecting what your soil and plants really need, focus on P for starters. Nitrogen (N) is easy to add later.
Phosphorus is a key nutrient for success in your edible or ornamental gardens. All plants have root systems, so they cannot do without this essential nutrient.
As we consider how much irrigation a plant really needs, whether it is a tomato or a maple tree, for each the stronger the root system the more efficient the water and nutrient uptake. Thus, the healthier plant depends on the root system.
Vegetables grown primarily for their roots – carrots, beets, turnips, garlic, potatoes, radish – may not even form a mature root in depleted soil. If nitrogen is high, leafy growth may be large and lush. But where is the root?
A tomato plant that grows to great heights may be something to talk about, but usually this indicates a soil high in nitrogen. While phosphorus may be available, for tomatoes the soil is out of balance. They respond to the nitrogen. Fruiting depends on more phosphorus, less nitrogen.
Flowering plants depend on phosphorus. In the world of perennials, some preferring strong summer sun may have prolonged bloom through undesirable heat spells if the soil has what they need. Similarly, perennials in shade may tolerate deeper shade than expected if the soil has plenty of phosphorus.
More flowering takes place, which should result, with pollination, in more fruits (or seeds) when the soil is balanced and the plants are healthy.
How much is enough? And what is the best way to add phosphorus? I have always used natural forms. Raw rock phosphate has been used with my fruit trees and ornamental trees and shrubs when they are planted. Its larger particles take longer to weather, making it a “slow release” fertilizer.
Commonly available, colloidal phosphate and soft rock phosphate are natural forms I use for flowers and vegetables. Finer particles supply nutrients sooner.
Four cups per plant, mixed with soil and compost plus a cup of oyster shell, works for either raw rock phosphate or soft rock or colloidal phosphate with the larger plants. If soil is being prepared for vegetables, herbs, perennials, or even annuals, 15-20 pounds per 100 square feet is an effective application rate. Plus 5 pounds oyster shell for the same area.
Natural phosphorus in the forms mentioned is not water soluble, so it’s important to add when soil is being prepared. Get it into the root zone!
When I was formulating “Carolyn’s Mix” for local gardeners, available at Rare Earth, phosphorus and oyster shell were added to a combination of mushroom compost and rice hulls. You may still add more colloidal phosphate at planting time in unimproved or depleted soils. Hard to overdo natural phosphorus! “Carolyn’s Mix Plus” I concocted for vegetable gardens, adding chicken manure to the original mix.
Remember that any compost can be “hot” when air is added. Front end loaders, dump trucks, and even your shovel add air when material is moved, even if it has been aged. Wet new piles or recently moved compost, and test for heat in a few days. Do not be in a hurry. Plants may be killed in newly activated compost.
Better yet, order your compost months ahead of when you will be using it. Good gardening takes planning and time. Slow down and enjoy the process.
Carolyn has gardened organically in Nevada County since 1977. A schedule of her gardening classes at Peaceful Valley Farm & Garden Supply in Grass Valley is available at www.carolynsingergardens.com. She is the author of the award-winning “The Seasoned Gardener, 5 decades of sustainable and practical garden wisdom”, and two volumes of “Deer in My Garden” (deer-resistant plants), available locally.