I've grown 'Courtasol' for a number of years. It's remained very dense and compact with good color even in a partly shady location. It would certainly stay under 5' as it tends to spread rather than grow taller, at least for me. After at least 6 years, mine is about 4' tall by 5' wide.

I grow 'Gold Tide' another low-grower. Grows about 3' tall and does spread readily. I don't think it blooms as well as the standard forsythias, but its nice.

The best I've seen is called 'Gold Peep'

Here is a link that might be useful: Forsythia cultivars

Mainegrower/Wendyb: you all alerted me to something I hadn't thought about - the spread of the plant. I was used to my upright Lynnwood Gold so hadn't considered that some of the newer Forsythias spread out wider then they are tall. That won't do in this space. Thanks for the heads up.
....Thank you for the link duncanmsu. It was helpful. Golden Peep's stated size is a little small for this space, but if those are northern measurements it may be taller in a warm zone. It is definitely on my short list along with Goldilocks. Hopefully someone else will chime in with experience on these two or other information....Maryl

Its not that they grow wide per se. I think any forsythia will spread once the shoots arch and touch the ground. Even my Lynwood Gold does re-root if left unpruned. So the shorter ones just touch the ground quicker because there is less distance to travel.

With my gold tide's I just periodically rip out the offshoots and pot up for friends or toss.

Forsythia 'Courtasol' and 'Goldtide' are the same cultivar - the English version presumably tacked on for the committed monolinguists.

In my experience, this forsythia definitely exhibits a horizontal growth habit, very different from the upright, arching habit of the more familiar large kinds. It spreads out by suckers as well with no need for branches to root after they touch the ground. It is, however, an easy plant to keep at just about any desired size through pruning once or twice ayear.

I have Fiesta Forsythia, its more upright than horizontal for me. It gets 3-5'...mine are 4' after 3 years.

The newer stems are red and the slightly variegated foilage is a nice bonus throughout the season.

Its a fairly heavy bloomer (most are)...pic is from two years ago. The flower look more yellow due to the sun.

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