I gather that suckerers can travel out to infinity. If you can keep them contained, about 5' between plants ought to do it for most varieties. Don't forget to stick bulbs in under their feet (early and late-blooming kinds).
Melissa

It depends on the look you are going for. Five to six feet is enough if the idea is to have a rose hedge with no more companion plants than groundcover and bulbs. The roses are somewhat contained by mowing, pavement or each other. Something like that is best in an out of the way corner since it won't look like anything after the roses bloom.

A more interesting, but logistically more difficult idea is to put the roses in a mixed perennial bed. This takes a lot more room between the roses, and requires roses that don't want to take over the world. However, the perennials can put on a show after the roses bloom, and the garden can have summer long interest.

It also depends on whether the gallicas are own-root or budded. On rootstock, they are much better contained (although they may escape) and much easier to mix in a border, as one sees in famous English gardens. Your soil makes a difference about how aggressively own-root gallicas will spread. In the Sacramento cemetery's sandy loam, my guess is that roses like Superb Tuscany would indeed spread to infinity! They are contained by the burial plot surrounds. In my silt-clay soil at home, they colonize more meekly and are contained only by digging out suckers that have spread too far (and potting them up and sharing them).

The idea of interplanting bulbs is intriguing. I've been struggling with several very visible plots with incredibly straggly Gallicas. Our climate does not encourage them to be beautiful, but they are ugly-as-sin from June through September. Some yield nice fall foliage colors, and the bare canes look ok in winter, as does fresh foliage in spring. I've planted a couple of ground covers for them to poke through, with mixed success. Any suggestions would be appreciated.

BTW, Superb Tuscany is drop-dead-gorgeous and has quite good foliage throughout the year. It probably helps that it is in part-shade, so the blooms don't fry as quickly and the foliage doesn't burn as much either. It blooms after all of our other Teas and Chinas and even the HPs are pooped, a lovely late-spring gift.
Anita

I struggle here with bulbs (not Gallicas) so don't have the underplantings I'd like. In western Washington state this worked wonderfully. In one bed I had snowdrops followed by hyacinths under the roses and so flowering season began in early spring, not in June. Clematis scrambling through the roses would probably be good, too, if you didn't want to grow them on an obelisk for height.
Anita, your roses must be on a flowering similar to mine: earliest roses starting at the end of April, warm-climate roses in May, once-blooming cold hardy old roses starting around mid-May and going on for about a month. Though no, you must get a lot of fall and early spring bloom that we don't have. My once-blooming roses like part shade, as do the Hybrid Musks.
I grow my roses in heavy clay and even suckering roses that are off their rootstocks are rarely so aggressive as to become pests (give me a few more years...). Summer drought with no watering may slow them down too.
My sunny garden is ugly as sin in the summer as well, and is likely to remain so until I get some flourishing trees and large shrubs going. These will cool the air and give me some shade and summer green. There's just not that much happening once it gets really hot and dry. There's lavender, of course, and it blooms in the summer, and all the aromatic plants for texture and fragrance and foliage color: rosemary, thyme, lavender cotton, teucrium. Possibilities might be late lilies, fall-blooming bulbs (crocuses, colchicums, sternbergia), Japanese anemones. And foliage plants like heucheras that look good even when not in bloom. Oh yes, cyclamen for fall and winter interest. Agapanthus. Clematis. These are plants that I know grow in mild temperate-Mediterranean gardens, as most I have here and some I had in western Washington. Hellebores. I don't know how they'd do in your climate, of course. If you're worried about plants being able to compete with the suckering roses, how about sweet violets, which are very tough as well as beautiful and fragrant? Put all the thugs together in one bed.
Melissa

Melissa,

I keep wondering whether you can grow Anemone de Caen. It is almost hardy here, lasting a winter or two with scant bloom. I think that you are a little warmer than we are. Also can you grow florist's ranunculus and freesias? Once I saw a photo of freesias growing wild under olive trees. It was beautiful. Ranunculus and freesias seem to be a little more tender, no hope of growing them outside here.

Cath

Hmmm, freesias, ranunculous and De Caen anemones - no use growing them here either....unless you are fairly dedicated - I find many of these tender bulbs do far better in pots under (cold) glass....although I have seen drifts of anemones in other people's gardens, just not mine. They all seem to drift into strange and wayward growing cycles, often producing leafage during the coldest times and failing to follow through with blooms.....or suddenly springing into growth in October.......or leafing out voluminously, then simply dying back.....or growing for one short season, never to be seen again (freesias, in particular).....or just failing completely.
Nonetheless, we must persevere and once again, there are the usual hopeful pots of ranunculous (Aviv forms), De Fokker anemones, bessera, babiana, ixia, supposedly treated freesias and various zephyranthes, lurking in the greenhouse for yet another trip on the disappointment merry-go-round.

Gallicas - well, depends which. However, they are amenable to certain bullying perennials elbowing a space between them - astrantias, herbaceous clems do especially well, penstemons, and the ever reliable alchemilla will always shelter beneath the arching canes. Don't fret too much about space - they will simply intermingle, tending to reach upright rather than flopping around and since all the colours mix in harmony, a delicious tangle will be the result.

I plant my gallicas 4-5' apart and mix in with perennials and bulbs as my other roses. Mine started as grafted roses but I planted the bud unions below soil not knowing any better at the time (some are more than 12 years old now) and they have gone own-root and sucker, but I diligently dig up suckers each year in late fall or early spring and try to keep each one contained in its allotted space (which works mostly but not perfectly, but generally looks tidy throughout most of the growing year and gives the perennials a chance).

Own root? One per half-acre! *laughs*

Cath,
To answer your question, I don't know. I've had Anemone coronaria (I think it was) and also freesias for a short while years ago, but they didn't last. This may have had as much to do with poor placement and soil preparation as with cold. We appear to be a solid Zone 8 as far as minimum temperatures go, though with plenty of winter chill. My guess is that these bulbs would want loose soil with good drainage in a protected spot, rather like what I give my Parma violets. I've never tried florist's ranunculus.
Melissa