I am hanging a water hose holder for a 50 foot all-rubber hose. This holder can be mounted with 6 screws (2 rows X 3 columns). Would it be necessary to try to at least get that middle column attached to a stud or should standard wall anchors be sufficient?
I would recommend just getting a stand. Once you get through stucco it's not sealed and moisture and air gets in and causes rotting behind the stucco. Most carpenters and cladders may tell you to just spray foam or some sort of sealant will do the trick. But I am a restocking specialist, I have the carpenter and fire flood and mold restoration experience. I tell you to think of it deeply, the stucco acts like cement it stretches and shrinks there for once the sealant is cracked it's not going to expand or shrink with the stucco. Some will tell you to fill it with stucco. But again unless you are the one who installed it to know the exact brand that was originally used there is different ingredients in different brands meaning again expansion and shrinkage are all off set. I know alot of people won't think it really matters one little hole. But moisture once behind the stucco becomes drops that can infiltrate the tightest spots and go far. Rotting everything behind it. But that's just my 2 cents based on almost 2 decades of experience dealing with this stuff.
Yes, you want to find a good solid stud to anchor into, because if the teenage animals that you live with are anything like the teenage animals that I live with they will not be kind to it.
The stucco is not strong enough to support anything...
(BTW, you can probably find a good stud under each side of your windows.)
This hose is not that heavy but yes you should try and hit 1 stud. 1 stud would easily support the weight. But what type of siding / sub siding? In some homes pre 50's with a sub siding of angled 1" I would not worry about hitting a stud. If a more modern home with ? Sub siding I would want to hit a stud on 1 point wether right left or center. I have seen some homes that had no sub siding because the wrap and exterior siding met code in the 70's I would absoulty want a stud in this case because there were thousands of siding failures in my area mostly the vinyl clad chip board and that stuff has no strength 25 years later and many houses had to be resided with some $ from class action lawsuits , but it will be best to hit at least 1 stud if possible. Since you have stucco what is the base, some are just chicken wire, prior to the 50's many were built with expanded steel lath , if that kind of exterior 3 rows by 2 would be fine, chicken wire stucco hit a stud or the first time you pull on the hose you may be shocked at the damage.