The soil mixture RU recommends per planting hole is as follows:
1. 1 (one) cup of 46% superphosphate
2. 1 (one) cup of dolomitic lime
3. 1 (one) cup of Mills' Magic Rose Mix
4. 1 (one) cup of gypsum
5. 1/4 part compost (approximately 2 gallons)
6. 1/4 part peat moss (approximately 2 gallons)
7. 1/4 part good top soil (approximately 2 gallons)
8. 1/4 part red clay if available...substitute with good grade of commercial potting soil
I'd be intrigued to understand why RU recommends potting soil as a substitute for red clay, since I think of red clay as dense and sticky (when moist) and potting soil is light and airy. Maybe it's because the perlite in potting soil retains moisture and clay also retains moisture? We'll have to ask Pat.
I presume the lime is added to counter the acidity of the superphosphate. Also, as noted on dolomiticlime.com, soil acidity in the U.S. generally tends to increase as one travels from the northwest to the southeast. As rainfall increases, bases like calcium, magnesium, potassium and sodium are leached out of the soil and replaced by hydrogen, so lime applications provide the following benefits:
- Provides an inexpensive source of calcium (Ca) and magnesium (Mg)
- Improves microbial activity (which produces organics)
- Improves nitrogen availability of phosphorous (P) and Mg
- Lime aids in the use of P which promotes root growth
- Liming increases soil structure and increases rates of air and water infiltration
Bringing this back to Nicolas, I was intrigued to read in A Rose Odyssey that some of the nurseries and growing fields he visited around the globe produced extraordinarily well developed roses despite the heavy, greasy clay and higher alkalinity found in the local soil.
