5 feet spacing for a hedge 7 or 8 feet otherwise.

I won't give you any exact numbers, but I'll keep re-posting this picture of this single plant and you can do with it what you will:

The other thing to consider is the amount of shade from tree, part sun is fine but not full shade.

also planting around a tree can be tricky as often times you are dealing with lots of roots. I've done it but can make planting hard.

Thank you all for your kind recommendations!

I'm thinking of keeping it around 4' tall and wide. How much should I trim in the fall to keep it blooming at 4'? How much does it grow in one season?

Once it reaches the size you want in late fall after the blooms go brown I would prune the stems to half.

Another option would be to get little lime which is a dwarf limelight which has a mature size you are looking for.

Hi kimivu,I cut mine back to about 3' each year and they still get to 9'...you might consider Little Lime topping off at 5/6'

I too found its really hard to contain it to a certain width and height.

That's why, I too, feel little lime, may be a better option.

Definitely Little Lime. I got 3-gallon potted Limelights this season and they're passing 4'

And remember that the oak tree is going to suck up nearly every drop of water you put down- any hydrangea is going to have to fight the tree for moisture. In a warm climate you will be watering way more than you think.

Ego45 used to be on GW and he was an excellent gardener. He had hydrangeas around a large tree. He started with very, very small hydrangeas.

As I recall, He used a cardboard box to retain the soil while they got their start. The box decomposed over a year or so. Very clever and effective.

Try a search for his name. I also reposted his post a few years ago. God knows where that is.

I used to mulch with cardboard every winter- finally a use for all my Amazon boxes, lol.

I loved it- it held moisture, suppressed weeds, and was simple to pick up and toss into the compost pile each spring when spreading the fresh pretty mulch- it is a tad unsightly.

The only reason I have had to stop is because a new dog will eat the cardboard, lunacy, I know. She's an idiot, but an idiot I'd rather not have an intestinal obstruction so I had to ditch the winter cardboard :(

Probably because it is bored or the cardboard absorbed food smells. But there are worse things that the dog could try to eat! Ha!!!

So I got some little lime. Is it safe to plant now? Our temperature is 98-100 F over here.

No. I keep anything purchased since late May (when temps hit mid 90s here) potted in bright shade and away from windy areas until lower temperatures arrive (Sept for me).

Technically, you can plant at anytime but practically, nah.

Summer is worst time for planting and with 100 heat good chance won't make it. If possible try waiting till September