Question about tree roots, its behaviour

I have this tree http://davesgarden.com/pdb/go/55692/index.html Underneath, about 10 feet or so from its trunk, I have one of my flowerbed area where I have some plants, including purple baloon flower, et al. When I dig up the area, I find many small rootlets of the tree. I think it is affecting the normal growth of my plants there as I feel they might be sucking out the nutrients and making the soil hard. The plants don't seem to be doing well. Also near to it is the Polyalthia longifolia and the Santalum album trees. If I improve the soil by changing it, will it help? Will not the roots of the trees get naturally attracted and move/grow towards the moisture [natuarally we will water that bed] and still affect the desired growth of the plants? What could be the solution? It is a big old tree.

Dinu, I don't know the habits of those trees in particular, but I can tell you about the trees I'm familiar with. The roots do the same thing.

We add soil around the base of a tree we want to plant under and then add the plants. You have to feed and water extra because the tree will draw off the new food and water source too. Also, make sure that the plants are compatible with the tree...sometimes the two do not mix...but another plant will do just fine. It takes extra work to have a planting under a tree, but it is so lovely, most folks don't mind.

As long as your plants are kept well watered, their roots shouldn't get forced out by the tree roots. Both should live together.

I have hostas planted under my maple tree and have the same problem with the fine, feeder roots. Some of the hostas are thriving while others had to be moved because they were dwindling away. A couple of tips I have learned-once a year stick a shovel or garden knife in the ground, making a circle around the plant. This cuts off the feeder roots. Eventually they will grow back but in the meantime your plants will have less competition. Also, water the whole area under the tree, not just by the plants. If you just water the plants, the tree roots will migrate to the area where the water is.

Yes, i think that is a pretty good suggestion. But do all parts of the roots absorb water or only what you call as feeder roots? I had removed clumps of those last year but now, whey I tried to dig around the plants, it had become hard again. Am thinking of changing the soil too. That may be the reason why my Columbines are not doing great.

Pruning the feeder roots is probably the best way to handle the problem. Use a flat spade with a sharpened edge to slice down 10-12 inches just before they reach the planting bed. This does need to be several feet away from the trunk, and you don't want to do it all the way around the tree unless it is still small. The tree will put put new feeder roots closer to the trunk and eventually you will have to do the pruning again.

As I told, the growing bed is about ten-15 feet away from the trunk and in a reasonably small area. The rest, I'm using as path. So, next time I dig out there, I will make sure to remove by cutting the little feeders. Thank you Jessamine.