I have a couple of azaleas that have the white looking leaves that I read about in this article, and it said to use fungicide. What kind should I use? At first it was just one plant, but now it appears to be spreading!
Neem oil makes an effective fungicide. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
What causes the browning on the tips of the leaves? Too much water? Too little water? Something else? I planted these from a very good nursery early in the spring.
It sounds like a nutrient issue. Give the plant some fertilizer. Also make sure the plant is getting enough water. It needs at least 1-2 inches of water a week.
Many leaves have a purple discoloration. How to treat?
It may also be caused by a lack of nutrients. Have the soil tested. It may be a phosphorous deficiency. Purple leaves/foliage are a sign for this deficiency. Regardless, adding a little phosphorous will not hurt the plant. Here is more information: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/phosphorus-plant-growth.htm
When should these outdoor-grown plants be trimmed back?
These articles should help with that: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/when-to-prune-a-gardenia.htm
https://www.gardeningknowhow.com/ornamental/shrubs/azalea/pruning-azaleas.htm
New azaleas were planted 4 months ago. Now there appear to be many tiny white spots on tops of leaves, looking as though the insides of the leaves are gone at the spots. Underneath there are tiny black spots, many of which can be scraped off with vigorous rubbing. The azaleas that were replaced had the same affliction. What is the problem and how should I treat it?
Sounds like it may be any one of the following pests: Mealybugs or scales, which commonly affect many types of plants both indoors and out. OR it could be attributed to the azalea bark scale. Neem oil is an effective treatment.
Here are some articles that you may find helpful: https://www.gardeningknowhow.com/plant-problems/pests/mealybugs-white-residue-on-plants-leaves.htm
https://www.gardeningknowhow.com/plant-problems/pests/scale-bug-how-to-control-plant-scale.htm
https://www.gardeningknowhow.com/ornamental/shrubs/azalea/azalea-bark-scale.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
The buds on my azaleas have turned brown and won't open.
It could be either botrytis or thrips. These articles will help:
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
http://plantclinic.cornell.edu/factsheets/botrytisblight.pdf
When can I trim my azaleas?
This article should help: https://www.gardeningknowhow.com/ornamental/shrubs/azalea/pruning-azaleas.htm