Hard pruning photinia
It's March 7 today. I whacked some very leggy (15 ft) photinia down to about 6 ft last fall, and they are coming back from that nicely but still scraggly at the bottom. If I take them back to around 2 ft in the next week or so, will they be able to take it? (They had leaf drop/fungus issues from not being pruned or sprayed for several years.)
Photinia responds well to hard pruning ("rejuvenation pruning"), but give it some time to recuperate between hard prunings. Discolored leaves are usually not fungal disease.
Like many shrubs, over-tall or leggy Photinias respond well to being cut down all within 8 or 12 inches of the ground, which is called "rejuvenation pruning" because it gives you a chance to completely start over with shaping the plant ("respond well" in this context means they usually survive and push up a lot of new growth). However, hard pruning does require the plant to use up a lot of stored energy to put out replacement growth, so since you recently cut the plants down from 15' to 6', we would suggest giving them a year to recover and store up energy before you do more hard pruning. Meanwhile, DO keep an eye on leggy new growth: cut out congested growth at the base (lots of space for air movement will substantially reduce fungal disease problems), and you can reduce long new shoots by half their length which will help appearance.
Apart from the severe pruning we're discussing, many people shear back their plants about 6" after the spring growth matures in order to prompt a second flush of that new-leaf red color.
As always, consider replacing oversized plants with smaller varieties or cultivars that won't require (as much) pruning: "Red Robin" is about half the height of the older "Birmingham", has good red color and good resistance to leaf spot--but still gets easily 12' or taller in the Northwest; "Indian Princess" has orange-red new leaves and is shorter. "Cracklin Red" is about 6'; "Little Red Robin" gets about 3'.
Regarding fungal disesases: There is a Photinia leaf spot fungus (Entomosporium mespili) which causes reddish-purple blotches with white/tan round dots in the center of the blotches, and can cause severe defoliation in the spring. It is best controlled on mature plants by pruning for air flow and keeping the fallen leaves raked up. But much more common is something called "physiological leaf spot," which is not a disease, but is apparently a natural response of Photinias to environmental stresses. Fungal sprays will not help; improved general plant care may help, but this is a very common condition and not susceptible to chemicals.
So do you think we could rejuvenation prune this fall since major prune was done last fall?
Rejuvenation pruning on a Photinia hedge will probably be fine if you have given it at least one good year to recover from earlier hard pruning; but do give it good care this spring/summer/and fall.