I have some seeds on order to start one of my hedges and I worry about how close I can take the hedge to the drain field given that the trees in question are normally species that grow much taller than they will be pruned to (mulberry, sea buckthorn, and siberian pea). I will be training and pruning them to be no taller than 6-8 feet, but I assume that the overall height doesn't necessarily mean that they will not be as deep rooted as they normally would be. Added to the fact that I am not 100% sure how large my drain field is or how much damage tree roots would cause, I wanted to make sure before I laid out my plan for this particular hedge.
I go back and forth on this same issue. I have not planted near my drain field, but I am going to have to decide soon. I have read and listened to everyone who says go for it, to those who say never get near the drain field. I don't have a great answer, but here are my guidelines for my planting this year. 1) I know that my lines are old and already have some issues so I am leaning towards a more conservative approach. 2) I am not going to plant anything in the drain field with edible root crops. 3) I am going to plant in the area of my drain field but I am going to maintain roots probably further away from lines than necessary.
There may be some info on the root systems of those three trees that you could look up. In general, they seem pretty tough and give me pause. If you're on the edge of the field, you may be alright, but, for example, I'm taking out a bunch of Rose of Sharon this year that was planted on the drain field just to be sure. 4 of the bushes were rather large and we've not had a problem, so there's that.
In the end it's all guess work. If you're keeping them small, that is certainly in your favor. It then becomes a yearly or bi-yearly necessity though.
My dad and I redo septic systems. If a tree is anywhere close, its roots will find it. The tree will be healthy, but the tank/line/d-box will become a twisted mass of roots that inhibit flow and proper operation. We've had to put in at least one new septic tank that was destroyed by trees. When we pulled the lid off, it looked like a rootbound potted tree with all the soil washed out. Just crush it and fill what we could with sand is all there is at that point. I would avoid it at all costs if possible. Septics around here are $4000 to $6000 for a normal house IF you have repair area.
The county septic inspectors will not say one way or another whether it is safe to garden over. Besides the possibility of tilling deeper into the panels at some point, the microbes and pathogens are subject to question. We were told to keep edibles at least 4 foot away from a drain line, and they dont bury them that deep.
I would shy away from it personally. This is one of those areas where I'd side with the conventionak wisdom as its a costly mistake. However, I'll tell you what I've done.
When I bought my house last year I had to get the septic replaced. A couple established trees were ripped out (plums), the system replaced, and the entire area covered in an extra 4 inches dirt as the new code required it. I didn't notice any areas with root issues, the trees were ripped out to allow room for equipment and because the new level of dirt would have killed them anyway. My property is narrow (75-80ft) but long. The new leach field occupied the middle third of my property. The first third I dedicated to conventional lawn for resale purposes as I plan on possibly renting this place one day. The back third I used for a forest garden and a few raised/trellised beds for grapes, raspberries, strawberries, etc. Not wanting to plant anything too deep rooted, I lightly tilled the leach field to knock down weeds and sowed a mix of wildflowers.
Waiting to see how this turns out, but the benefit will be several fold. One, it should attract pollinators and beneficials, aiding my productive plantings. Two, it should just look pretty lol. Three, perhaps most important to me, it saves the area from being overrun by grass that I have to mow.
Doesn't quite address your issue, but I guess what I'm trying to say is steer clear of planting near septic. If you do all could go well, but it could also be a several thousand dollar mistake. Not to mention seeing any progress you may make could be damaged or set back by the equipment used to replace the septic.
The county septic inspectors will not say one way or another whether it is safe to garden over.
The field itself (if it's anything like the ones we have here) requires grass to work properly. The moisture is absorbed through the grass and perspires through the leaves - This is over simplifying the process, it's far more complex than that. Perhaps someone with more experience could chime in?
Here, when we have long periods of drought, planting trees or anything with roots near the sceptic field or tank would be the worst idea imaginable. Especially hardy trees like mulberries or willows with huge roots. They would seek out the moisture in the dry months. Even if we kept the trees pruned, it would still create liability for the next owners of the property who may not be aware of septic maintenance and let the trees grow - roots grow - roots grow into septic field - may get us in future legal trouble for planting the trees too close.
Then again, when we arrived, there are all sorts of trees bordering the septic field. Neighbours have a big line of tall conifers along 4 meters away on one side, and an ancient apple tree, probably planted in the 1860s or 1870s (that's ancient for here) two meters away on the other side. The field use to flood every summer before we moved here, but like I mentioned we get drought. The field has been replaced once before we got here, but it made no difference to the flooding. When we moved here we did two things (none of which involved getting rid of trees). First we had the tank pumped - first time since the early 1960s that it had been pumped. It was solid, about fifty/fifty earthworms and earth - sadly we aren't allowed to keep the soil . The second thing was to put sheep on the pasture. They improved the health of the grass in about two years. Now the grass is only dead for 2 months of the year instead of 6. Those two months are also when the well is just about empty, so we don't use much water then anyway.
There are a lot of fancy tricks and tips to use for sceptic health - everything from buying the correct toilet paper and cleaning products (according to the guy with the honey truck, certain shampoos really bugger up the system) to having the right sort of lawn (or in my case, mixed pasture grasses). And then different systems work differently and different parts of the world have different systems... it can get confusing. Some of the writers here may have systems that don't rely on grass like mine do. In that case, having garden on top may work just fine.
It's a good thing you are thinking about it. I've met many people in our area who don't even know they have a septic field until they smell the stink of a broken one. We could do with some more public education here - congratulations, you bought a house with a septic field, here's what you need to know.
As for trees - my opinion is that it depends a lot on your weather patterns. With lots of drought, it's more likely to be a problem then somewhere with reasonable rainfall year round. Also, it may be to your advantage to know the local regulations regarding septic systems. Some places have laws against planting xyz, such and such a distance from the system.
I share a similar view to what's been posted already. The first year at my place I put in a garden along the edge of where my leaching field is, not really knowing much about it. I didn't end up putting anything there except compost, which volunteered pumpkins, squash and some tomatoes. I used the pumpkins for halloween, and left the tomatoes and squash. I ate wild raspberries from the same area and didn't get sick but it's one of those things I go back and forth on and can't seem to decide. I have decided to just use the space for flowers - and right over top of the leaching field is just grass - and you can really tell where the waste goes, since the grass is super lush and green in one area and just kind of regular in the rest.
In terms of the roots scenario - I definitely am more apt to not plant anything with roots near it because I don't want to pay a zillion dollars to replace it - but that being said, my septic and leaching system has an ENORMOUS white pine right smack in the middle. How it has not ruined the thing already - I have no idea. So I am sure there are exceptions - and I have wanted to believe there must be some permaculture solution to it all, but I haven't yet found anything I'm comfortable with aside from planting wildflowers for the bees and butterflies etc. I know geoff lawton made the point that if you put a reed bed in between where you want to grow and where the leaching bed is, it acts as a natural filter. Not always practical in every space though.
Don't. Absolutely don't. The roots will eventually fill the drainfield pipes, and even if the septic tank doesn't fill up with roots too, it will stop working right. Roots can travel a long way as it is; don't encourage them by planting them right on top of a root lure, which is what a drainfield amounts to.
Also, fer ghu's sakes don't be cultivating and plowing over your drainfield; you can wind up crushing the pipes or helping soil work in through the drain holes, which does them no good either.
Probably the single biggest killer of septic systems is anything growing over 'em other than grass. (And from experience, I can tell you that grass with extremely deep roots like Bermuda grass can also clog a drainfield.)
It may seem fine for some years, even decades, as the septic system can take a long time to back up from the impaired flow depending on the surrounding soil and how well it drains. But sooner or later, those roots WILL kill it. And you may not be able to replace it -- in a lot of areas septics are becoming prohibited and you can't get a permit for a new unit, or there simply isn't enough suitable space for a drainfield. And then if you can't repair the old one, you're screwed.
Siberian pea trees are deep-rooted regardless of size; that's one reason why they're so drought-tolerant.
Seriously. Don't do it. Can't emphasize enough.
yet another victim of Obsessive Weeding Disorder
I carry this gun in case a vending machine doesn't give me my fritos. This gun and this tiny ad: