Basically, I'm planting about 9 fruit trees in my backyard, which is about 10K square feet. Great size, but unfortunately I have a large septic field, as do my neighbors just on the other side of my fences. So basically, I'm trying to make sure I don't plant any trees anywhere near too close to the fields.

I plan to keep the trees pruned down to about 10 feet, tops, but about half of them have max heights in the 15-20 foot range without pruning (the others are more like 8-12 ft anyways). So whether the roots will grow 15-20 feet radius from the tree or the 10 foot height I keep them at is obviously pretty key here in my layout. Depending on what they do, I just planned to take that number and add 50%, just to be absolutely sure the roots don't eventually spread to the fields.

Also, about how fast do roots spread typically on fruit trees, in terms of length per year? I'll be planting a couple apples, peach, nectarine, plums, almond, olive, and cherry.

Any help would be much appreciated.

===>>> if your first generalization is wrong.. i dont know where to go from there ....

check out the link from a while back ...

i dont understand how pruning the canopy .. will change the trees genetic predisposition to growing roots ...

perhaps some more info will help ....

whats the native soil ... how old is the septic system ...

are the trees dwarf ??? do you know the understock???

and there are some fruit professionals in the fruit forum.. which i have never seen in the tree forum ... and tree peeps do things different that tree peeps.. regardless. post wherever you want ...

good luck

ken

Fruit trees are a PITA.

I have been to orchards. Much like a chicken coup or corn field they have little to do with nature or natural. Them guys have a science going on. Make yourself familiar with it.

As Ken already said, that's just wrong.

"...half of them have max heights in the 15-20 foot range without pruning (the others are more like 8-12 ft anyways)..."
combined with
"I'll be planting a couple apples, peach, nectarine, plums, almond, olive, and cherry."

Where are you getting your info? You can keep apples pretty small using the right rootstock, but what about the rest of your trees?

"...I have a large septic field..."

You may not have to worry too much about this, depending on the design of your septic field. Newer designs tend to be more resistant to root damage, and tree roots tend to grow mostly in the top couple of feet of soil (depending on the type of tree, the type of soil, etc.) You probably do need to keep the trees a reasonable distance from the septic field, but you don't necessarily have to make sure that there are no roots near the area. Consult your septic system installer for more details about your particular system, and ask him for his input. Do keep the trees far away from the septic tank.

Basically I wasn't sure because I was thinking if you keep the tree shorter and well pruned, I would assume it wouldn't need as many nutrients as it would if it were 1/3 bigger or whatever with a lot more branches, hence it wouldn't need to grow as large of a root structure to maintain the tree's needs; so I would think it possible that it wouldn't waste energy growing more/longer roots than it needs. That was my thought process anyways, apparently wrong?

====>"what's the native soil ... how old is the septic system ... "

The soil is fairly compact, not sandy at all, and is surprisingly rocky once I got to digging a little. This isn't apparent from what's on top, which reveals no rocks anywhere until about 4-6 inches deep, just grass on dirt. I live in the PNW at the base of the Cascade Mountains so get quite a lot of rain, though summers are generally very sunny. I don't seem to have to water my lawn more than once or twice late in the summer to keep it green as at least once a week during the summer there will be a good heavy downpour followed by lots of sun most of the rest of the days (based on last summer).

The septic field is pretty new (3 years old, only used so far for 2 years and lightly for the year I've been here, as it's just my wife and I, yet is a field/tank for a 4 bedroom, 4 bath house, despite the house being just 3 bedroom and 2.5 bath).

The holes I have marked out now have the two closest trees to the field being a semi-dwarf santa rosa plum at 18 feet from the start of the field, then a Garden Prince Almond (dwarf, 10-12 ft max supposedly) about 30 ft from the field, then everything else (2 honeycrisp apples, 3-1 pear, goldmine nectarine, red baron peach, 1 plumcot, and 1 arbequina olive, 4-1 cherry) will be about 40-50 feet from the field, with most having a projected max height of 15-25 ft without pruning.

Oh, and technically the olive will be about 25 ft from the actual septic tank itself (a 3 tank system clustered together), but I'm guessing, unless the tanks have an existing leak which I doubt with it being so new, the tree roots can't effect this?

Does that seem safe enough?

Your logic is not totally wrong about the root size relative to the amount of growth, but there is a limit to how much difference it will make. A smaller tree (overall, not just height) will grow roots more slowly than a similar large tree.

I didn't do any calculations on your lot size versus planting distances, but it sure sounds like you are planting at very good distances. I'm a little surprised you can stay that far away from a "large septic field", with that many trees, and that size lot. But, if you can, I think you are 100% safe. Even if a tiny root makes it that far, it won't hurt a thing.