WHERE IT ALL BEGINS: THE SOIL - Growing Chinese Vegetables in Your Own Backyard - page 213

Phosphorus
The second number in a fertilizer formula stands for phosphorus. (Technically, it stands
for the amount of phosphate, the most common form of phosphorus, but many garden-
ers erroneously use the terms interchangeably.)
Phosphorus makes everything else work in a plant's metabolism. In addition, it pro-
motes strong stems and flowers, and aids in setting fruit. It is essential to root crops
since it directly affects development of both feeder and main roots. If you get skinny
roots instead of fat radishes, your soil is probably deficient in phosphorus.
Phosphorus is easy to apply and should always be included when side-dressing root
vegetables. It's readily available in the form of rock phosphate, which is comparatively
inexpensive. Additional sources are fish and shell-fish. You don't have to bury fish
heads in your garden, though; it's much easier to use fish emulsion. Some brands of
fish emulsion are formulated to be higher in phosphorus (with a grade of 2-4-1, for ex-
ample). Another source is bone meal.
Potassium
The last of the big three nutrients is potassium. Again, the number in the fertilizer grade
technically stands for potash, a common form of potassium, but many gardeners use the
terms interchangeably.
Its chief function is to promote healthy, sturdy plants that are more resistant to
whatever stresses come along. It makes plants more winter hardy; it acts like the an-
tifreeze in your car and so is particularly important to vegetables like garlic that over-
winter in the ground.
A sufficient supply of potassium makes plants more resistant to diseases and less
affected by extremes in temperature. It gives roots the strength to push deeply into the
soil and is the most important of the three fertilizers for the production of satisfactory
root crops.
Potassium is readily obtained if you have a source for wood ashes (which also add
lime); they can be incorporated in the soil and used as a mulch. Be warned that in large
quantities, wood ashes (as well as synthetic forms of potassium) can burn plant roots.
Also, wood ashes raise soil pH so they may be helpful for acidic soils but should not be
used on alkaline soils. Greensand and sulfate of potash-magnesia (langbeinite, sold as
SulPo-Mag or K-Mag) are other organic sources that are readily available. Fish emul-
sion and fish-and-seaweed fertilizers also contain potassium.
Micronutrients
Other nutrients are essential but are needed in smaller amounts. These include calcium,
magnesium, sulfur, and iron. A few more are needed in only trace amounts, so they're