Respectfully, I have to disagree with the above prescription for water. How much water the soil can hold depends on the soil type, and how much to add depends also on how moist it is. But typically, in your midwestern location, one inch per week is adequate with high temperatures running in the 80s or low 90s. Plants could use maybe 1.3 inches with higher temps, or low humidity and wind. One inch is 4-5 gallons per square yard. With sandy soil, water less than an inch at a time, but more often (at least twice a week), as it can't retain much water. 3" at a single application is way excessive. With temps in the 80s, I water less than one inch per week and my roses never stop growing vigorously. In Florida with sandy soil and temps in the mid-90s, we watered 3/4 of an inch every three days if it didn't rain. Every gardener should have a rain gauge.

Right, don't fertilize until they have recovered and have put out plenty of leaves. Bloom Buster is the wrong kind of fertilizer--regular Miracle Gro or Miracle Gro for Roses is fine, or any reasonably balanced fertilizer such as 10-10-10 or 18-6-12. Watering correctly is the most important thing. Keep a 2" mulch of leaves or bark around the roses. When the soil under the mulch feels dry-ish, water thoroughly with 2-3 gallons for small plants or 5 gallons for larger, plus or minus for extremely hot or very mild, cloudy weather. Usually once a week is fine. For new plants, I divide the ration in half and water twice a week.

SW -- a photo would be very helpful, but considering it's Knockout, and considering that you're in Houston, I'll almost bet money that the problem is chili thrips. Do they have black veins and blackish stripes or spots on the stems? (see http://www.houstonrose.org/ctko1.jpg) While the Knockout series tends to be highly resistant to fungus diseases, they are extraordinarily susceptible to chili thrips. If that's the problem, you really have only three choices: 1. Replace them with a different variety. 2. Live with it and realize you're going to have a lot of dieback, regularly. Or 3. Spray for them.

Hey! Don't despair! It's quite likely it's got nothing to do with you or anything you're doing; it may well just be an issue there in that location that needs a bit of detective work to identify. A few questions that may help us get to the bottom of it: Can you have close look at the leaves, please, and tell us: - whether (what I think I see) the yellowing is starting in the leaf veins while surrounding leaf tissue remains green for a while, before turning yellow and dropping? - Is it the newer leaves mainly that are yellow, getting better/greener as they get older, or vice versa - the young leaves normal/green, but yellowing as they get older? - Also, how compacted clay-ey is that soil of yours? When it's dry, does it become almost rock hard? - If your home is new, is there a possibility there could be builders' rubble under your garden bed, eg lumps of concrete, bricks and so on, which could be leaching lime, making the soil in that area extra alkaline, esp after rain? - (Maybe others can answer this one; I'm def not an expert) - that yellow mottling of leaves wouldn't be Rose Mosaic Virus, would it? I have to confess that although Adelaide isn't really that far from Melbourne, I've never spent any real time there (in Melbourne). Everyone complains about the cold weather there, but I think that might just be Australians' idea of cold, which may not be quite the same as in places with actual cold climates! :-)