Why own-root roses are healthier than grafted?
Potash didn't work for disease-prone own-root, such as Gruss an Teplitz (the parent of Dr. Huey). Gruss an Teplitz is known for blackspots and mildew, that's where Dr. Huey get his genes from. My 16 bands are clean, no aphids, except for Gruss ... he's covered with aphids, skinny weak stems, thin leaves. I gave Gruss calcium via gypsum, didn't help. I gave Gruss Sulfate of potash... didn't help. Gruss can't pick up potassium nor calcium ... I wonder about his offspring, Dr. Huey rootstock.
My 52+ own-roots are healthier than the 15 hybrid teas GRAFTED on Dr. Huey in my last acidic clay garden. Grafted roses don't have maximum access to water and nutrients, since it has to pass UP a restricted bud union. That bud union could be damaged by dryness in storage, winter, or soil acidity.
Someone asked if own-root is healthier. My answer is yes, since it's easier to find an own-root suitable for one's soil and climate.
1) Folks with acidic clay reported GRAFTED on Dr. Huey's decline ...multiflora rootstock is best for acidic soil.
2) I put a Knock-out grafted on Dr. Huey in a wet alkaline clay & poor drainage. That went downhill. I moved it, and put an own-root Romantica, very healthy, gave me 70+ blooms in 1st year.
3) I planted an grafted hybrid tea in a pot. It's clean in that dry pot, until I moved into wet clay, topped with acidic leaves ... broke out in BS instantly. I dug that up, and Dr. Huey's root shrank.
4) I killed a Knock-out grafted on Dr. Huey in a wet bed ... Dr. Huey was gone, it grew its own-root. Compare that to my killing a Knock-out in a DRY SPOT: it has both Dr. Huey and own-root together.
5) The bigger the root is compared to the top growth, the healthier it is. Own-roots are smaller, thus less demand on water and nutrients. Dr. Huey is a cross between Gruss an Teplitz (disease-fest) and Hybrid Wichurana (large climber), so its rootstock produce massive top growth, more susceptible to diseases.
My William Shakespeare own-root is small like a mini-rose, and blooms constantly. Compare that to much bigger WS grafted, which means more demand on water and nutrients ... and if these NOT met, diseases will occur. Dr. Huey is listed as susceptible to mildew.
I moved plenty of roses in my zone 5a: the difference between own-root and grafted-on-Dr.Huey: Own-root spread out, some horizontally from the main trunk, and can survive wet clay better. It's more efficient to transport water from a spreading root. Branches bloom better if trained sideway, rather than upward. Sap and nutrients flow better if it doesn't have to fight gravity.
Grafted roots have to go UP through a bud union, it's not an efficient water-transport system of HAVING TO PASS through that knob, esp. when that bud union is damaged. Grafted-on-Dr. Huey is great for a dry climate like California, but it's a big decline in Dr. Huey if buried deep in a cold zone, or wet clay. In my last house of acidic clay, I dug up a dozen BS-fest grafted hybrid teas, all roots shrank.
Below is own-roots Mary Magdalene (great myrrh scent), and Marie Pavie (musk scent that perfume my garden). Marie is in front, Mary is the bush behind - both are always clean even in humid and rainy weather:
Below is William Shakespeare 2000 own-root, it's small like a mini-rose, but blooms constantly in partial shade. I watered it less than 5 times per year, not much demand on fertilizer either.