Thanks for your comments, Oilpainter. I think I can manage to put a small amount of soil on the roots nearest to the trunk, and maybe "finesse" the ones farther away. I am really hoping to take care of this for many years.
Ann

You'd probably get better advice specific to your situation if you called in an arborist to assess the situation, and see whether your conditions would support losing 4 feet of driveway, chopping/grinding roots within this area, and adding new curbing to a certain depth to prevent further surface root growth breaking up the rest of your asphalt driveway. Adding new soil to a limited depth over mature pine tree roots is usually not a problem if the soil is well draining and not over 4 to 6 inches in depth, but over a short time, the tree roots will also fully colonize this new soil and fill it with roots as well, particularly if you will be irrigating it to try and get something to grow here. If the area is partially shaded, and you don't get much in the way of frost, I might suggest some drought tolerant, root tolerant and shade tolerant ground covers for this area such as Crassula multicava, Pelargonium tomentosum or Aptenia to cover the ground; all of these are really tough plants that will compete with a pine tree roots if given some initial TLC at time of planting, and occasional supplemental watering.

Asphalt is actually somewhat porous to both air and water, and tree roots actually follow the underside of paving because it tends to stay moister longer as it does not get as hot or dry as bare soil. Therefor tree roots tend to seek out such locations to mine the extra moisture.

If you were to add a new edging to try and prevent the worst of larger surface roots, it would probably be best to do it as reinforced concrete to a minimum 18 inch depth, with sufficient rebar to hold it all together. This will not prevent feeder surface roots from going under it, but typically will restrain the bigger roots from damaging the asphalt. Again, I'd suggest consulting an arborist first, and get their more informed opinion on best way to proceed.

Unfortunately many more common Pine species in California are notorious for being surface rooting and very efficient destroyers of asphalt paving. Are your neighbor's pine trees by chance Italian Stone Pines? In my experience, these are some of the worst offenders, and I wouldn't want one anywhere near paving of any type.

Bahia,
Thanks for your thoughts, especially the plant suggestions. I did come to the same conclusion that I needed expert advice on site, and just met with soemone who has a landscaping and tree service business. The tree(s) are Torrey Pines, old and tall. He suggested tearing up the asphalt in the worst area (also farthest away from the trunk), grinding out some roots and moving the edge out to mostly extend over the area. Then build a footing of reinforced concrete (1 foot deep)for the new retaining wall.
Your point about the cut roots sending out feeders into the new terrain is well taken. I am thinking drought resistant and/or non-living sculpture.
Ann

Why on earth would you not want to kill such intrusive trees? Not that you should just go ahead and do that, but these trees need to be removed and, if trees in that location are a good thing, replaced with more neighbourly species.

Anything you do on or above the ground is a complete waste of time. As Bahia says much more moderately than I am prone to doing, the tree roots will colonize whatever there is.

KarinL

karin, such irreverance! Would you chainsaw your neighbor's trees? Torrey pines, no less! Here people go to jail for that. Perhaps the trees should never have been planted in this location, but too late now...

http://en.wikipedia.org/wiki/Torrey_Pine

karinl,
The trees are many years older than I am. In a neighboring town it is unlawful to cut them down. When they were planted, my driveway didn't exist. When we moved into our house 23+ years ago, there wasn't evidence of a problem. Over time, and with the neighbor's watering habits, they have grown into my property. Although there is a lot of debris and the asphalt has developed into a problem, I still like the trees. Monarch butterflies come here, attracted to them. Hawks nest in them. And in an area which used to be known as the Flower Capital (of so. cal, or of cal, or...of the world?? can't remember), the place has turned into an overdeveloped mess. So they offer me beauty, privacy and a sense of time. One could argue that I am the invader...Rather than just kill the thing (at over $2K to remove), I am looking for a compromise so we can both exist.
Ann

Torrey Pines are certainly worth preserving in a garden setting, as long as they aren't dangerous to the house, and I respect the OP's attitude that she wants to work with them, rather than eliminate them. If you had any personal experience with how beautifully sculptural these trees are, and also how rare they are in nature, I don't think you would be so quick to condemn them, KarinL... The specimen Torrey Pines planted at the San Francisco Botanic Garden in the native section are simply spectacular, and seem to grow much larger here than they do in habitat along the coast. Certainly they are not a pine for a small sized garden as they can become huge, but have no tolerance of a climate such as Seattle or Vancouver, where it is too cold and wet in winter to really suit them.

It is not impossible to grow plants under heavily surface rooting pines in a southern California beach setting, but it is a fact that whatever is selected will need some help to compete long term with the new roots growing into raised fill, and the planting choices will certainly do better if they tolerate drought and heavy root competition. The plants I mentioned certainly do that, and of course there are always many other plants that could be considered as well. Perhaps native low growing Manzanita species would also be appropriate, or even something as common as Carmel Creeper Ceanothus, or one of the Correa cultivars. In any case, I would suggest that if it isn't succulents, the new plants will probably establish better if they are planted as at least one gallon sizes and given a ring of drip emitters and supplemental drip irrigation to help the new plants compete with the tree roots.

It wouldn't have the same aesthetics, but you might also consider using massed plantings of bromeliads in this location, as they really don't mind tree roots as competition at all, and could be minimimally irrigated with short bursts of overhead spray without the need to really wet the soil at all, and will accomodate to growing in medium shade easily. The one downside to plants that "catch" falling leaves and pine needles is that they may always look a bit messy, but this isn't necessarily detrimental to the health of the plants/bromeliads. I'd probably prefer to plant things that can absorb the pine needles rather than having to rake them/blow them off, and the succulent ground covers such as Crassula multicava or Sedum dendroideum v. praeltum do this well, without needing much water or deep soils.

Well, as a self-professed conifer enthusiast I hate to admit that I have not, in fact, encountered the Torrey Pine before, but that might be a bit of a function of locale.

But even so... not really reverent, no :-) Although I could be induced to modify my views to suggest planting a new exemplar or two of such a special tree on your own property now, in preparation for a day when these may fall or be felled, or in fact moving the driveway if that can be done. I think Bahia's ideas of underplanting are practical, but hardscape likely is not. It will, as you say, have to be redone periodically. It's going to be a forest floor, not a garden, and not a smooth driveway.

I have a lot of experience with tree idolatry/reverence, having been sacrificed to it for several years (as regulars of this forum have heard more than once). A neighbour's tree, standing at a respectful distance from their house but close to and swallowing our house, also having us in its windshadow, its 60-foot trunk leaning threateningly over our childrens' bedrooms... and the rank hopelessness of gardening underneath it... when there was any time to garden between having to clean out what I could get to of the eaves or sweeping the porch and front hall of the constant flow of tree debris... none of which accrued to the actual tree owners, living windward. I learned all our legal rights too late to assert them with the inconsiderate boors who owned the house at that time, but mercifully the house was sold to reasonable people who realized within 10 minutes of conversation that they could not mitigate the effects of the tree on us, and that those effects were onerous, and agreed to take it down (we paid for it, they repaid us half).

Actually, we sort of mirrored your progress, but in fewer years (this was a Chamaecyparis lawsoniana). I loved the shade of that tree from the time we moved in 17 years ago for about 12 years. But it grew, though I barely realized it. Then one day I realized that I could no longer see the corner of my house, and I had ceded fully half my front yard to a forest understory. I don't have a big enough yard that I was willing to do that. And the other issues became unbearable - we didn't sleep much on windy winter nights, and when two identical trees nearby went down in the Dec 2006 windstorm (fortunately missing neighbouring houses), we decided to revere our lives instead of the tree.

But the moral is this: trees don't co-exist. They dominate. If you are willing to be dominated for the benefits of the tree, and it poses no actual threat other than to your driveway, then you are doing the right thing. But the dominance will progress; this is not a stagnant situation. Understand that you will continually be in retreat, the tree continually on the advance. You may be entirely willing to be in constant retreat - give up 4 feet of your driveway now, more later. There is no way to solve the problem of advancing roots "for good" or to "smother the roots." The tree is a perfect competitor (except with a chainsaw, or the wind).

No one, not even me, wants to go wantonly around cutting big trees, but the alternative is sometimes moving driveways and houses - not always practical, and trees do grow again. I am a big fan of planting new trees well before removing old ones, so the wildlife needs and others can still be met when the big trees go.

KarinL

You might want to look into a product similar to the one I have linked to below. I have used a root barrier with success. Success depends on going deep enough (the root barrier comes in various sizes with 18" being the minimum) so be prepared for some serious digging and clean root pruning.

Here is a link that might be useful: root barrier

Thank you all for your comments and ideas. Bahia, the new area will not be in much shade; the location is roughly south-facing. Two major (>12 inch diameter) tree limbs which were extended over into the driveway have been removed, leaving smaller, sparse ones above. In mid-summer there is some light shade later in the day. I like your idea about massing bromiliads; I actually have a lot of them, but they are not the full sun types.

KarinL, I understand your point of view. We have another neighbor who has used his trees and plants to block our ocean view and generally make our lives miserable. The plants are just doing what they are programmed to do. You can call it domination; I tend to think of it as survival.

Inkognito, Thanks for the root barrier link. How expensive is that stuff? You mention you have used something similar; how long have you had it successfully in place?

Ann

In case Tony/Incognito doesn't answer right away about the herbicide impregnated root barrier, this product is used in urban street plantings where surface rooting is to be discouraged, and it actually does last for a very long time, but would probably need to extend at least 2 to 3 feet down vertically, or until you hit bedrock or a soil depth where there isn't enough oxygen in the soil to encourage tree root growth. The possibility always exists that tree roots can still grow under it and then into the new area, but typically it is the main principal roots that tend to serve as anchor roots for the tree's stability that do the most damage to pavement, and on older trees like pines these tend to stay near the surface, but that will vary greatly on your soil type and soil moisture conditions at different depths. Your arborist/consultant should be able to advise you more specifically if this herbicide impregnated root barrier makes sense to add against the new curb/wall to help protect it.

I wouldn't rule out other sun loving bromeliads for this sunny situation, things like the more terrestrial growing Puya or Dyckia species might be good choices, and it also sounds like this thin soil, sunny area full of tree roots might be an excellent location for clumps of Agaves such as A. bracteosa, A. 'Sharkskin' or A. parryii cultivars, or in combination with things like Echeveria agavoides or Bulbine frutescens. Aloes such as A. saponaria or A. striata would also do well there.

All of these plants would grow better if planted in a new layer of topsoil added over the tree roots, and given at least a monthly periodic good soak, or more often depending on how quickly/lushly you prefer them to look. California natives such as Mimulus aurantiacus, Salvia clevelandii or S. leucophylla 'Pt. Sal' could also look good here, or even more adventurous plantings like Metrosideros collina 'Springfire' or Metrosideros collina 'Tahiti'. A really cool looking green fuzzy flowered Aloe such as A. tomentosa would probably also do well there, or other Aloes such as A. castanea, A. camperi, A. rubroviolacea or A. vanbalenii.

Sounds like the right time to add to the "woodland" setting the Torrey Pines are providing. Follow their lead -- if they want some of the asphalt gone, break it up and cart it off. Plant some woodland groundcovers or low woodland plants.

For the lady in BC: the human animal is a high creative and adaptive species. It can adjust to plant species which are not as adaptable.

Bahia,
Thanks again for the plant suggestions. This is the first time I have visited this forum, and I really appreciate the help you have kindly extended.

The area in question is connected to existing bank plantings of Rosemary officianalis; Acacia longifolia, (behind); a lone Leptospermum laevigatum (which might look better with a few more near it); and some blue fescue. Further away is a fig tree and beyond that is some lavender under a row of oleanders.

Although a succulent/rock garden is appealing, it may look a bit odd with the rest of the plants. I may be able to tie it in by extending the succulents across the front span of the area. I am also thinking of some low-growing ceanothis (i.e., maritimus); Artemisia "Powis Castle"; and maybe some bronze Phormium. Also a Grevillea, such as "Poorinda Constance".

Hopefully I am seeing a certified arborist today, to get his opinion of the Torrey Pine situation.
Ann

I suspected that I might be going off on tangents, regarding what you already had in the garden, and how any new plantings might relate to them. At first I had thought you were probably dealing with shade as well as roots, having sun actually does give you the options of using the plants you just listed. The reason I had given you lists of bromeliads and succulents as a starting point is actually a very pragmatic one; they are superbly adapted to root competition while needing little additional irrigation, and will tolerate poor soils or in this case, soils where the tree roots have first dibs on the available nutrients and water. The plants you list will probably also work, but most of them will need more supplemental soil, fertilizer and water to compete effectively with the pine tree roots, especially since they are to be planted underneath a mature pine in soil that is probably full of roots. It would make a huge difference if all the plants were starting out at the same time, when the tree has such a head start, this usually means that you will need to compensate, or look for plants that can tolerate the extra difficulties of getting established with aggressive tree roots. At least you are dealing with a pine species that is not intolerant of summer irrigation, and is less likely to suffer from phytopthera fungi attacks or oak root fungus.

Also I don't know if pine bark beetles are a problem with Torrey pines in your area, but I might mention if they are, (they love to attack our native Monterey Pines here), it is best to only prune pines in winter, so the sap doesn't attract them to attack.

In reference to the root barriers, I have found the best are polyethylene, they are much more durable, flexible, and they don't crack. Compared to polypropolene which is a cheap plastic that breaks very easily. I was told of a company called Century Products from a friend who supplies these particular barriers they have the best prices and a good quality root barrier I can depend on. I also liked how the panels connected to each other in a zipper-like fashion so minor roots could not grow in between. Definitely something to look into if you haven't already solved your problem. Hope everything works out!

Heres a link to Century Products facebook page with more information about there products, company phone number, and a link to the official website. Hope it helps!
http://www.facebook.com/pages/Century-Root-Barrier/293265244104728

Ann, I don't have specific considerations for you, but am wondering if a different type of driveway could be installed, using permeable materials.....or a section removed and replaced with permeable. Wish I'd seen pictures of your area to grasp the scope. I've read about 'driveable grass', have seen a large pasture with it installed to handle tour busses at an estate here in the Atlanta area that hosts large groups. Code ordinances where you are may dictate what driveway surfaces should be, but if so, perhaps you could get a variance.

This is a most interesting conundrum you're facing. I'm glad you're approaching it so thoroughly and thoughtfully. My suggestion is just another consideration for you.

Rosie, Sugar Hill, GA

Thank you RosieW and Rma1029--It has been a long time since my original post, so I was surprised to hear from you!

I ended up having a trench dug close to the side of the driveway, and a strong black plastic sheet was inserted vertically (not sure if it was polyethylene or polypropolene). I had a modular fake stone retaining wall built on top of that, and the area was back-filled with some local dirt. I am growing mostly succulents, a grevellia also is happy there, and some blue fesque in a corner which receives more water.
Thank you all for your comments.
Ann

Hi Gardnergal:) any chance you're still living with the Torrey Pines and their roots? I am wondering whether your trench and retaining wall worked out for you.

I'm wanting to put in a vegetable garden where there was lawn and Torrey Pine roots had raised up the ground so it wasn't level anymore. I'm concerned that the roots will take over the vegetable garden as they reach for the water and nutrients I provide for the edibles. Any advice?