I think you are answering your own question! : ) I think maybe it is not so much the dead space as I have seen that done well on TV, but the scale that is bothering you. Mock oranges are about 8x8, right? That would make a real difference to the look in that bed! It would creat an anchor, sort of marrying the deck to the ground and the garden. I say go for that, and adjust the other plants as needed. With the spacing, which I am not sure of there, would it look better to move your prized Diana out as a keynote of the bed, the featured plant?

The three mockorange I purchased say they will grow to 3-4'x3-4', so they would fill at least half of the blank space under the deck. I agree, I need a backdrop, b/c the things in my back border are just lost in that space right now.

If only Diana would grow quicker! She was planted in honor of my Grandpa (Rose of Sharon was his favorite), so I'm not opposed to moving her but want to keep her in this same bed. Would you move Diana into the forefront of the bed knowing that she'll eventually be 10-12 feet tall? I think you're right though.. it is the scale that is bothering me, but this was the biggest Diana I could buy in my area (5 gal pot).

I totally agree with you on the space under the deck being a big factor. I was thinking that you could get 2 panels of lattice, and cut them with a jigsaw so when they are put up, side-by-side, there is a somewhat low arched opening that they create. Even if it's only 4 or 5 feet high, it could look like an entrance into "fairyland" --no one can see it's just empty space beyond. This would create a visual barrier that's there year-round. As your mock orange bushes get bigger, you could take the lattice arch away if you wished. If you kept it up, you could create a stone pathway leading towards it. Instead of the archway, you could also use narrow sections of lattice, maybe 4 of them, along the deck to interrupt the view.

Whatever you decide, I'm sure it's going to create a focal point that wins over the deck, and that is going to make that garden area look great.
{{gwi:716238}}

Can I throw out a totaly wild suggestion? How about planting a garden UNDER the deck? I try to utilize every space in my smallish garden, and it looks like under your deck would be a wonderful place for a shade garden. You could put alot of golden and silver foliage (such as from Sum & Substance hosta and Jack Frost Brunnera) to illuminate under there. You could even add a focal point, like a statue or fountain, in there that you could see from this angle. And maybe put a Clematis on that deck pole to disguise that. I had a strip along the west side of my house I just hated. So I took out the piles of river rocks and now have a drought tolerant bed out there. I love it!
But, if thats not really what you were going after I think repeating what you did with the trellises and Morning Glories would look good. And it wouldnt take up too much space for other things.
CMK

I don't think I'd go with any more trellissing or lattice - you've got an awful lot of vertical and horizontal lines going on there...siding, deck support pillars, deck railings, iron fencing. But you've got the start of something good that just needs a little organization.

Looks like a good bed for some well chosen and placed rock groupings; not a rock garden, but accent pieces for things to be planted against, among, or to clamber over.

It's unlikely the mock orange will stop growing at the 4x4 foot stage, but still may not give you the background height you're looking for any time soon. They're great shrubs, and the fragrance intoxicating but probably put to better advantage as a grouping elsewhere in the bed where you need a backdrop. If they're still in pots, move them around until something clicks.

Would you consider a specimen, focal point tree - like a Japanese Maple (Acer Palmatum) out toward the middle of the bed which would divert attention from the black hole of the underdeck? Many of those have beautifully colored deeply cut foliage, interesting branching habits, different growth rates etc. and can be planted around quite effectively.

Daylilies companion nicely with nepetas, Russian sages, Veronicas, peonies. Delphiniums would give you height with gorgeous blooms - beautuful against the wrought iron fence.