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Does anyone know of a source for determining the size of a root zone for shrubs, trees, etc. that would be planted adjacent to a concrete slab foundation? I can find many sources that give height and canopy sizes but never see the root zones mentioned. My concern would be with finding plants that will not damage my foundation as they grow...
It'll depend on your soil type and things like that, roots will travel farther faster in sand than they will in clay, but if you're just looking for a rough guideline, assuming what AJNTEXAS posted is probably a decent guesstimate. If you're growing things that are really tall but very skinny (like Italian Cypress), their roots will probably spread farther than twice the width. And if you're growing something that isn't too tall but has really wide spreading branches, then the roots may be closer to the same spread as the top. But it's harder to predict what roots will do than it is to predict what the top will do, that's why you don't find that information on specific plants.
The thing you really need to be careful of is whether the plant has troublemaking roots that like to lift up foundations and get into water pipes. That really has very little to do with the root spread, some things might tend to have a big root spread but their roots really aren't very strong and invasive, so they won't lift your foundation even if they're close to it. Best thing to do is post a list of the plants you're considering and ask if anyone knows if they cause problems with foundations, water pipes, etc. Or try googling, if it's a plant that's notorious for causing problems it'll come up on a search like that too.
For foundation plantings, the roots of any trees and shrubs that you plant are going to be close enough to the foundation that if they have badly behaved roots they're going to cause problems for you, so I really think you need to worry about that and not what the root spread is, if you just go off root spread you won't be able to plant much of anything bigger than perennials.
I appreciate your input. We are putting in a new bed on the east side of our house next spring. The original owners of this house had planted a cherry tree way too close to the house so we took it down last winter. It was a 30 yr. old tree and we were digging the roots of that up for the new bed. The interesting thing was that the roots (and some were as large as my arm) followed the concrete slab but did not appear to enter or go under the foundation. Still, it was a pain to dig them and I wouldn't want us or anyone else to go through that ordeal again!
The best way to find out the root spread of trees is to, a) find out about the root growth, ie, does that particular tree spread it's roots out or down,, some species of trees have very shallow root that will not go down, you sometimes see the real root growth after a storm, there is a massive tree fallen by storm, but the roots are in tact and on show because the roots were going almost over the surface of the soil, others need really deep soil as their roots need to go deep down into the soil, b) there are other questions to ask about specific trees, like do they grow in moisture retentive soil, an indication that they will need to search far, deep and wide for the amount of moisture they need, hence the reason they wont grow in dry desert areas but happy beside streams or drains, the type of wood a tree produces also has a bearing on the type of roots, hard woods have tough roots and can if strong enough penetrate anything that it's roots grow beside like concrete, foundations, tarmac etc, other things like cherry have surface roots that are not as strong to get into foundations or open drains, but the roots can grow the full length of a wall just because it needs the room to maintain the top spread of the canopy the tree has grown, but it wont penetrate the wall, so really, what is above the ground as far as trees are concerned does not mean a massive problem under the soil, but as for how far a root will grow is different to how it grows, the general rule of thumb is, find the mature height of a tree, that is after 10 to 15 years, and the width of the canopy after the same time, and you have the rough equivalent of the root spread the tree will take up to support that large canopy, but different trees have different root requirements. I guess the moral of the story is, when you want to plant a garden tree, and we all need them for air benefit, landscape and beauty, the best thing to do is get good advice like from the parks department, the tree nurseries or from books at the library that will explain what that tree will do for you, what size and when it will flower or fruit etc, it is well worth the trouble, we have all seen a lovely tree at the garden centers and wanted to buy it, we do, then when we move away from that home, we sometimes leave a huge problem for the next people who live in the property, as you have found in the case of the cherry, but the cherry has done no harm except it has outgrown it's space and sadly, there is lots of trees we grow in small gardens that will do that anyway, unless we choose a type specially bread for small gardens. good luck. hope this helps you out a bit and you can choose something that will give you years of pleasure just as the cherry has done for years before it got too big. WeeNel.
Another thing to think about is the ph. Some plantings fare better in acid soil, they are not happy near cement.
What are you thinking of planting? California lilac - actually from New Zealand I think, does very well against a house, though I would plant it at least 2 ft. from the foundation. Am sure one of the other BC denizens will know the real name. When you are thinking of purchasing things, the Hobbs nursery (not the correct name) is quite wonderful in terms of knowledge. Again am sure someone will jump in with the right name.
California lilacs (genus Ceanothus) are native to California. I'm sure there are some Ceanothus species that aren't CA natives, but a good number of them are, it's one of our more popular native plants.
