Luis gave a fantastic comparison, but forgot to mention that the mophead (blue/pink) hydrangeas love water. That is why they have hydra in their name.

On the other hand if the soil is too moist, azaleas will get root rot. Drainage is much more critical with azaleas. Some azaleas tolerate moisture. They are the swamp azaleas like R. viscosum and R. vaysei. I grow R. viscosum with my hydrangeas in a moist area with underground springs. Even my oakleaf hydrangea is tolerating this.

Yes, they are compatible.
This is the great combo if you properly space and site both type of plants.
I have a fairly large bed (about 450-500 sf) made almost completely out of deciduous or semi-deciduous azaleas and all kind of hydrangeas (oakleafs, paniculatas, macros and serratas) with astilbes and hostas in between.
They are interplanted in a such way that shorter azaleas (up to 2') serves as a filler between medium height (4-5') hydrangeas and the taller azaleas and hydrangeas forming a backdrop.
As Luis and Rhodyman correctly pointed out, the major trick is to create proper drainage for azaleas, but it's doable if you determined (in my case it was relatively easy since bed has a natural sloping toward the center, so I have a heavy concentration of hydrangeas in a center).
BTW, word 'hydrangea' was formed by combining two words from a different languages, Latin 'hydr' (water) + Greek 'angeion'(vessel) which has nothing to do with hydrangeas water requirements, but rather a reference for the shape of its seeds that closely resemble water vessels used by ancient Greeks and Romans.

Combining them will work out better if you plant drifts of several specimens of each kind instead of one of each in alternation. It will look better and the hydrangeas will not overpower the azaleas as easily.

ego is correct. I stand corrected, hydrangea does come from water vessel which describes the seeds, but most people never see the seeds since most of the over 600 named cultivars are varieties of Hydrangea macrophylla selected to only have large sterile flowers in their flowerheads. The association of hydrangea with hydra is used as a reminder that most hydrangeas like water.

Bigleaf hydrangea [H. macrophylla] is a water-demanding plant for the moderate water-use zones of the landscape. Water whenever the plant begins to wilt in the absence of rainfall. The leaves will begin to droop if the soil is too dry. Too much water and the leaves begin to get black marks on the edges. The avoidance of plant stress is particularly important during the spring months when the flower heads are forming.

I have a bed with hydrangeas and azaleas (along with hostas) and everyone appears to be happy so far. I think placement is the most important consideration. My bed starts out flat on top (where the hydrangeas are planted) and slopes down to the bottom (where the hostas are located)--in the middle we have planted a line of azaleas. So far so good. :)

Thanks for letting me bring this old discussion back to life. I would like to plant a fairly long strip above a retaining wall with azaleas or rhodos, hydrangeas and hostas. After reading here that placement is crucial to them being able to live together, I need some advice. I read that one person put the hydrangeas in the back, hostas in the front and azaleas in the middle, so all would have the best drainage. Our space has a downward slop on one end but levels out toward the other, with a Japanese Maple on the level end. The garden needs to look balanced from both the top and the bottom sides, since we have paths in both areas. How can I put these plants together so that they will also look good from the "back" side? Thanks in advance for your help!!

On 2nd thought, I measured the width of that area, and it's only 4 feet wide. Should I stick with either azaleas/rhodos, or hydrangeas, with hostas bordering? I think it might be too full with full grown plants! I have a hydrangea garden, and had one rhodo when we bought the house, but it died by the next spring. I'd really like to start a collection of either azaleas or rhodos.

I grow blue hydrangeas, and after confining them to my so called "blue" garden for several years, decided to include them in my woodland, along with rhododendrons, azaleas, kalmias, and camellias.
If you are starting from scratch, you may want to consider the kinds of azaleas and rhododendrons to grow with your hydrangeas. In 36 years of gardening, I have never killed a Kurume azalea by overwatering. And I am guilty of overwatering, as my first love as a gardener is a lush, green lawn. If my plants get in the way of the sprinkler, so be it.
If I were planning a border, or island garden, with hydrangeas and azaleas, I would plant some Kurumes, which in my zone provide flowers peaking around Mother's Day, and would plant some of the later flowering deciduous azaleas that contain viscosum in their genes. Viscosum does grow well in wet areas. You could also try Weston's Lemon Drop, viscosum 'Betty Cummins.' These should provide blooms at the same time as the hydrangeas, making for some nice color effects.

>In 36 years of gardening, I have never killed a Kurume azalea by overwatering.

I wish I could say that. We killed two of them, not so much by overwatering, but simply by getting a reasonable amount of rain. We were totally new to growing azaleas at the time, though I'd read a book on growing them. We figured that the fact that this area of the yard (next to the house) was well elevated and also on a bit of a slope, so that it would fit the azaleas' needs. Not so.

The planting area was total clay that we'd dragged there from excavated clay in building the house. Clay, total clay. Of course, we made some nice dirt in the holes for the azaleas, according to what I'd read...

Those holes functioned as good-sized pots; the surrounding clay didn't absorb the water that stood in those pots either. Water would stand there even if the last time it rained was days ago. The varieties were Hinodigiris. We learned a lot through this experience! I dug out that whole area, mixed in organics and sand, installed a drainage pipe to take the excess water into other areas of the yard, and dumped lots more dirt to elevate even more the spot where the azaleas were planted. Worked great, and all plants since then haven't gotten too wet... though some have had to be replaced do to insufficient watering during a drought.

You can't overwater any azaleas, camellias, or rhododendrons PROVIDED they are situated where the water its roots have access to has good drainage!

Best wishes,
Mary

Hi carolinamary,

I agree, I wouldn't plant a Kurume azalea in my fishpond.

What I am trying to do here is, given the considerable variation in moisture tolerance within the genus, point out some that may be more tolerant of the moisture that the hydrangeas will receive; for example R. viscosum.

If the hybrids of viscosum, many of which bloom in my garden at the same time as my hydrangeas, exhibit a similar degree of moisture tolerance, they would make for some nice color companions.

I have a wet area with underground springs. It is planted in hydrangeas and R. viscosum and its hybrids such as Weston's Lemon Drop. They are all doing well. Previously I had the deciduous azaleas Klondike and Gibraltar growing in the same area and they thrived.

This topic becomes more intriguing with each post. I’ve always thought that a grove of deciduous azaleas, designed with the goal of peak bloom around July 4, would be different and attractive.
I think I’ll put this plan into action next Spring, with the addition of hydrangeas, lilies, and daylilies.

Deciduous plants planted as foundation plants don't work very well visually in the winter unless they have a very good branching pattern. Hydrangeas fail in that respect.
Mike

Do coffee grounds provide acid for hydrangeas and azaleas?

Nope! Used coffee grounds are relatively neutral in pH. Any acidity is expressed with the coffee itself.

Many, many, many years ago, Starbuck's had some packages for the coffee grounds that included a notice which mentioned that most of the acidity was removed during the brewing process and that they provided minimal amounts of acidity. But feel free to sprinkle some around if you want. Be aware that some pooches love it and go berserk when you do that! Hee, hee. hee!