That's an odd proportion- so wide. You're probably looking at a grouping of three shrubs. And they don't just "stop" at 4-6 feet.

That said, the possibilities are endless and unless you narrow it down somehow you're gonna end up with a list of hundreds to choose from. So specify a flower color or if you want broadleaved evergreens or something climbing.

If it was me I'd do three conifers or evergreens for year round presence, then add a clematis or something low to give color.

Or I'd use an antique rose on it's own roots- they always combine well with split rails.

Or if winter interest isn't a consideration Limelight hydrangeas would be outstanding and you can keep them to size with pruning. Oakleafs work. Or any of the paniculatas or Annabelles.

For a huge fall display Lespedeza, for spring azaleas, Zebra miscanthus grass would be near care free, pieris, kerria sprawl beautifully, and so on.

See what I mean? So. Many. Choices.

would like summer bloom if I could specify season blooming perennial would not like to go much higher than 5' width can be just about any preferably flowering more than evergreen in an mostly sunny area. Although would not rule out a different colored Ornamental grass. Looking to put something at each post (three posts altogether).

this is the split rail project.. right ...

many shrubs have a very great potential .... make sure you take any suggestions to google IMAGEs ... and see what the future potential is ...

also.. many shrubs are spring bloomers ... it might be hard to find mid or late summer bloomers ...

and due to size.. keep in mind traffic sight line issues ....

ken

a summer bloomer would be nice

was thinking of a Quick Fire Hydrangeas just not sure when you can plant them

Hypericum flower in summer, mine are flowering right now...they might be a bit short for you though. Without knowing more, I can recommend a specific one.

recommend away!! I would like a perennial 3-4 maybe even 5' high summer bloom easy care zone 6b Roses are beautiful against a spilt rail fence however if I did have my choice I would rather stay away from them

Hypericum 'Hidcote', the commonest seen over here, will grow to 5 feet and is evergreen in our climate. I believe they drop their leaves in colder climates.

St. John's wort

Yes, that's the common name for the genus. But there are countless species and many hybrids which range from tiny alpines to large shrubs. If you do decide to buy one you need to get an appropriate plant. And to do that you need to use the specific name. The common name won't ensure you get a suitable specimen.

that is why I was also considering Dwarf Quick Fire or Lace cap Hydrangea

Hypericum is a large genus as Floral pointed out. There's pretty much one for every purpose (except possibly pure shade..and I'm not sure of that).

The flowers can be quite unique, as in the hypericum frondosum above. It is semi-evergreen here with shiny green leaves, has attractive peeling bark, and a naturally tight habit. Should reach 4-6 at maturity (4 years or so).

are there any in this variety than bloom longer than June-July timeframe??

Some of the less ornamental (imo) hypericums bloom for longer periods. I can't say that I personally have grown those. I prefer habit that's attractive year round.

Very very very few woody shrubs flower more than six weeks of the year. I can't think of any that are hardy (and I mean long lasting and vigorous, vs zone) that would fit the need. Those that do, are either barely hardy (dwarf crepe myrtles) or relatively weak and require lots of maintenance (aka roses or buddleja). Other possibilities are weed menaces like ROS, which I fight every year from my neighbors.

probably why I am in on the dwarf Hydrangea Quick fire long blooming time it says

Well not to blow holes in your theory, but the hydrangeas (pretty much all of them), have a short bloom time. The key is the bracts don't fall off, they just fade and dry there. To me (and this is just me), it's as if I have a plastic plant fading in the sun.

And, those hydrangea seem to prefer shade from the brutal midsummer sun. and lots of water. So, they're certainly not carefree. They're also rangy and will tend to have flowers only in the top parts of the plants. They're unattractive other than the flowers.

But in the end, it's what floats your boat...not mine :)

What about hibiscus moscheutos paired with a spirea?

Imo, that would work well (a mixture of pseudoshrub and shrub). It would still not be carefree, the swamp rosemallow needs ample water to keep looking pretty good. We don't really know where the OP is...this wouldn't do in Texas or Arizona for instance.

Of course if you're doing that, you could include some late flowering asters or rudbeckias to give a fall interest as well. Oh, and bulbs for an early spring presence...voila a perennial border.

Here my regular Quickfire hydrangea starts blooming right around July 1 and blooms until frost, a full 4 months. They start white and move through shades of pink to a deep rose. I don't know how they do in zone 7 as far as full sun, but all my Hydrangea paniculata varieties grow in at least 10 hours of summer sun. Perhaps Barron is thinking of types of H. macrophylla or perhaps H. paniculatas like Little Quickfire suffer more in his zone 7. It also could vary according to where you are. Zone 7 on Cape Cod or NJ is less harsh than areas that have drier air, clay soil, and more extreme temperatures.

You might want to ask on the hydrangea forum about growing H. paniculata in your state in zone 7.

Yes, that's a good thought. Most things look awful and tired if exposed to full summer sun here (obviously there are exceptions). The summer sun is brutal here. Cultivated cacti usually prefer some shade here. I have a few Malvacea that look good and fresh, and a few other natives. That's one thing I noticed when I vacationed up North, how fresh everything looks when not beat down by the sun.

I do have Hydrangeas at my home (not quickfire) and they seem to do well. I am in RI

Yep, your climate is so drastically different than mine, my advise may not apply at all. You might as well be in a different country :)

Hydrangea do well here, but do appreciate afternoon shade.