The issue of tree roots damaging foundations is usually grossly overstated, often by those who have little actual knowledge of the plants in question. If your foundation is structurally sound - poured in place concrete with no cracking, etc. - virtually NO tree roots are of concern, regardless of the size of the tree. Once they hit a solid surface, they simply change direction. Problems or issues with foundation damage are more likely attributable to subsidence or the swelling/shrinking of the surrounding soil due to changes in moisture levels. But trees often get blamed even though they are not the culprits :-)

Stone fruit trees planted 3 feet from the foundation should not cause any problems, especially with citation root stock. Citation produces very few roots. The problem comes when planting trees 3 or 4 feet from the house that grows to 20 inch diameter. They will push up the ground 4 or 5 inches. But that is only on big trees with lots of roots.

In my cool summer climate stone fruit are often deliberately grown right up against house walls as espalier or fans in order to take advantage of the reflected warmth.

Good info everyone, thanks.

Though they may or may not cause a problem for your foundation, they can cause a problem for your plumbing. Trust me, you really don't want to experience a mainline break! It's extremely expensive. I had a mainline break due to tree roots invading my pipes in March 2018. It flooded the entire 1st floor of my house with sewer water. Not only did we have to have our plumbing redone, but the lower 2' - 3' of wall in every single room of the 1st floor taken out, all of the tile & laminate taken up, carpet removed, our shower replaced, all of our kitchen cabinets & bathroom cabinets replaced, and many of our belongings were ruined from being saturated too. Thank God for home owner's insurance, because the grand total was close to $150,000, with about $65,000 of it being our responsibility!

The older gentleman that lives across the street from us just had his mainline break. The only trees he has in his yard are citrus trees. His back yard has about 6 orange & grapefruit trees. He's also having to have his plumbing re-done, & the inside of his home re-modeled.

We just had a huge oak tree taken down in our back yard last month. The arborist said that after working at his job for over 30 years, he would have no trees in his yard. I do miss having a tree & the shade, so am doing research to find something that will be the least invasive. So far I'm not having much luck.....

While all of this is great advice, nobody actually responded to the question...how wide do the roots go...google searches say nectarines go 4 feet deep, but don't say how wide. I need to know this too, for an unfettered tree because I want to plant back from a retaining wall, and presume that in the future, there may be owners who don't constantly prune the tree to keep it under control.

The question was answered, if in a rather roundabout way :-) There is no matrix for root spread based on species - there are simply too many variables that will factor into the equation. Lateral roots - those responsible for accessing needed soil moisture and nutrients - will extend as far as they require to get what they need. Suffice it to say that they will extend beyond the canopy spread or dripline, sometimes well beyond. And pruning of top growth will have minimal impact on the extent of this expansion.

Stone fruits are usually grafted and often on a dwarfing rootstock. This will limit the root spread to some degree. A 15' tree will not develop a spreading root system to the same extent a 40' tree would.

Many fruit trees are espaliered or grown on a flat, 2 dimensional plane, often directly against a wall, in which case the base of the tree is only inches away from the wall. In this case, the roots will grow in the direction that offers no obstruction, so away from the wall, not into it or through it!

There is a general rule of thumb governing the siting of a tree, any tree, and that is no closer to a structure or another tree than one half the mature canopy spread. But that is to protect the canopy (and the structure) from damage or the need for unnecessary or 'constant' pruning. There is NO rule of thumb for siting based on root spread, for the reasons already outlined.