How long should it take to root red tips using the water method?
Generally, these plants take about 6 weeks to root in soil, give or take. I imagine this would apply for water as well, though it could be earlier. You'll have to be patient since cuttings may not show any root development at all and then pop up all at once when you least expect.
How to treat powdery mildew on red tips.
These articles will help:
https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm
https://www.gardeningknowhow.com/problems/get-the-cure-for-powdery-mildew.htm
I planted 125 red tips last year and all but two made it. This spring they looked nice and green with new red on top, but they are starting to look weak. I live in Texas, and we have had a lot of rain lately, so I cut out my watering. I have not pruned them to help growth, don't know if I should and how to. So what can I do to get the green back and get them to grow taller faster? They are passed the first year now and have not grown very much. What am I doing wrong?
If you cut your plant back, you may actually see an increase in growth. Prune your Photinia anytime between spring and early fall, with late spring/early summer more acceptable. Red Tips are excellent candidates for rejuvenation pruning. To rejuvenate the plant, cut it all the way back to the ground...to about 6 inches from the ground. It should grow back nicely and you can expect to see 3 to 4 feet of new growth the very first year.
We have an established photinia (Red Robin) tree, which we have in a pot and it has become quite dense. We are intending to prune this but wondered if there is a good time to do this. Also, it is a tree rather than a bush and has developed a few leaves growing from about mid way up the trunk. We want to take a cutting from this to hopefully have some more of this variety and wanted to know how/when to do this and whether we should remove the leaves from the trunk or not?
This article will help you:
https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-root-cuttings-from-various-shrubs-bushes-and-trees.htm
How big does a photinia red tip get?
On average, these shrubs grow to about 8-10 feet tall with a similar spread if kept unpruned.
Will red-tip photinia survive the cold winters of southern Maine? How often does it need pruning?
It will need protection in severe cold. They are generally hardy only to 0 degrees F. Growing zones for your state range anywhere from 3-5 (eastern parts include some Zone 6). This being the case, I would suggest growing the shrub in a container, which can be overwintered indoors, or the garage.
You can prune it back anytime between spring and fall, with late spring/early summer being the most ideal. This article will also help:
https://www.gardeningknowhow.com/ornamental/shrubs/photinia/growing-red-tip-photinia.htm
Am trying to make a hedge with this plant. I was reading online and it says these plants bloom. Mine have not. I live in Oregon on the coast. The soil is sandy. When I planted, I mixed in compost and topsoil in the ground. They have been in the ground for three years and have not grown very much at all, probably about seven inches. They look healthy but are not really growing. Can you help?
It may be an issue where they are not getting quite enough light. This would suppress blooming and would also slow the growth. They may also be lacking nutrients.
This article has some other suggestions on why it may not be blooming:
https://www.gardeningknowhow.com/plant-problems/environmental/plant-not-blooming.htm