I have 20 7-ft high photinias with a disease planted close to my house, which may be the cause of my foundation problems. Do I need to dig up the roots? The bark is very hard.
From what I understand, these shrubs have a fairly heavy, or extensive, root system so it is possible that they could be interfering with your foundation but only if they were planted within 5 ft. or less of your home. If they are diseased, it is likely from a fungus, which is common in these shrubs. While treatment is possible, I would recommend transplanting them elsewhere if your foundation is being affected by the roots.
I would first try treating the fungus issue so they are somewhat healthy prior to moving. You might also need to prune them back by about a third. These articles will help: https://www.gardeningknowhow.com/ornamental/shrubs/photinia/photinia-leaf-spot.htm
I live in southeastern Pa.
For red tip photinias, feed them a balanced fertilizer and one that is aimed at acid-loving plants. An even fertilizer like 8-8-8 would be good. Fertilize once in spring and once in early fall.
How much a distance should they be from one another?
Fall planting is usually better in warmer climates, while spring planting is a good idea in colder regions. The shrubs should be spaced 3-4 feet apart.
I have 12 red-tips in my yard and would like to place more in other locations, but I have never gotten any new plants by reproduction. So how does the red-tip multiply?
Rooting the cuttings is much easier. As long as the stem you are cutting is healthy, you should not have any problems propagating it. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/shrubs/photinia/growing-red-tip-photinia.htm
Sow seed in a cold frame in fall, or root semi-ripe cuttings in early summer using bottom heat. Most gardeners find it easier to root cuttings than to propagate by seed
We planted photinias 6 weeks ago to create a hedge. They have grown only a little and I'm wondering when we should give them the first prune. Can you help?
Newly planted trees and shrubs usually don't start rapid growth immediately, they need time to acclimate and become established. I would wait until next spring before trimming them for the first time.
I found an old house place (civil war era) that had what looked like red tips everywhere. Identical in every way except in the leaf structure and grows slower. Any ideas what it may be? The leaf has the same colorations and length but sort of pointed like a holly. My father who owned a nursery said he thought it was a forerunner to the red tip.
While this doesn't answer your question, I found this article on different photinia's interesting: http://www.clemson.edu/extension/hgic/plants/landscape/shrubs/hgic1081.html
What fungicide would you use on photinia if they have the purple spots on them?
I personally like neem oil as a fungicide. Here is more information: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm