Soil and Bed Preparation for Growing Dahlias

Page 14

In the event that a professional soil test has not been done, three other approaches to determining fertilizer needs are available.

Purchase a soil test kit from a garden catalog sales company or a local garden center and do a soil test and interpretation using the instructions enclosed. Such tests are rough estimates, but better than nothing. The tests are easy to do and do not take much time. They are usually limited to testing for pH, Nitrogen, Phosphate, and Potassium.

Based on observations of plants from the previous year, determine the nutrient deficiency from plant nutrient deficiency symptoms observed. See Reading Plant Health for Deficiency Symptoms for a comprehensive listing of nutrient deficiency symptoms. A major shortcoming of this approach is that the type of deficiency may be known, but how deficient it is will not be known.
Plant nutrient deficiency symptoms for "nitrogen", "phosphate", and "potassium" are:

Symptoms are mostly generalized over whole plant; plant light green; lower leaves are yellow; growth is thin and slender; symptoms appear first on lower leaves and work upward.

Deficiency

Ammonium Nitrate 34 N

Plant is dull green, often developing red and purple colors; lower leaves sometimes yellow, drying to greenish brown or black colors; growth is stunted.

Deficiency

Super Phosphate - 45 P

Symptoms are mostly localized; mottled or chlorotic leaves with small spots of dead tissue, usually at tips and between veins; leaf edges may roll up; squatty and stunted growth.

Deficiency

Soluble Potash 60%

Guessing typically gives unsatisfactory results. Plants may grow, but frequently are not vigorous and produce small blossoms.

Continued on next page.

Reading Plant Health, Improving Your Garden Soil, Ortho Books 1992, Page 13.