I haven’t gotten any answers on GardenWeb yet, and I did a quick search on clematis and tree roots I found this statement below. Note what it says about tree roots (bolded):

Clematis have a reputation for being difficult to grow, however, like any other plant, if their needs can be met by the site and proper care, they will thrive. Clematis require full sun to grow best (6+ hours direct sun per day) though some dappled shade during the heat of the day is beneficial. Flowers of some red and blue large-flowered hybrids and the bicolors fade badly if they get too much sun (such as ‘Nelly Moser,’ ‘Hagley Hybrid’ and ‘Hybrida Sieboldiana’) and these should be planted in eastern exposures or partial shade. The site should be open enough to allow for air movement around the plants. Soil should be rich and well-draining with a pH close to neutral (7.0). Though the plant’s stems and foliage should be in sun, the roots like a cool, moist environment. With the exception of C. montana, clematis do not compete well with large tree roots. Most clematis will require staking so the twining leaf petioles can cling and climb upward, though some gardeners choose to let the plants sprawl over the ground, over woodpiles, other plants, etc.

The entire document is helpful. Click here for a web link. Here’s what it says about fertilizing:

Clematis may seem a bit slow to establish. In the first season, there may be little growth and few or no blooms. However, it is important to get the roots well established. Fertilize annually for rapid growth during establishment with a 3:1:2 or 4:1:2 ratio fertilizer. Apply one-half pound of a 15-5-5 fertilizer to the soil in the 50 square feet surrounding each plant. Fertilization may not be needed or desired once the plant is established and growing well. Plants will need about one inch of water per week during the growing season applied through irrigation or rainfall for good establishment.

I’m thinking I might want to dig them up and plant them in a planter box to get them away from the tree roots. Maybe I’ll move them to the backyard to grow on the big arbor.

Here’s more on fertilization from Ketzel Levine:

Food!
Clematis are what we call “heavy feeders.” The large-flowered hybrids are particularly piggy. Maurice Horn recommends either a once-every-three month application of a granular, slow-release fertilizer (“a hailstorm’s worth”), or monthly application of over-the-counter tomato food (it’s slightly higher in potash), spring through summer/early fall. Don’t fertilize after September, as the clematis needs to harden off for winter. The small-flowered hybrids are less maintenance, plenty happy with just one spring feed (or an annual topdressing of composted manure; no clematis would turn that down).