Rain garden for driveway runoff- excavated soil for garden?

The bottom of my driveway floods. There is a swale next to it which helps, but it fills quickly. I am excavating for a rain garden in this area where I will plant native grasses and flowers for wildlife and mulch material. The idea is that the rain garden will be fed by the water that would otherwise pool on my driveway. I have some garden beds for which I need soil. I am doing them as hugelkulturs (Paul would scoff at their puniness). 18" beds with the bottom 10 inches or so as wood. I already filled 3 beds with excavated soil from this area. 1 for non-edible flowers, the others I am planning on growing ginger and tropical greens (shaded area - these all like shade). The other 3 beds that I haven't filled yet are for summer annuals (sweet potatoes, eggplant, okra, long beans, etc.). I've been thinking though... SHOULD I be growing food in this excavated soil? I can't imagine it's too contaminated, but there are certainly some types of nasties leaking from cars, getting picked up by rain hitting the driveway, and some of it entering the swale and soaking into this area.
Thanks for any insights.
Mike

A picture is worth 1000 words so maybe some pictures might help.

My first thought was what material is your driveway made of?

How busy is your street to contaminate the soil?

I like your idea for native grasses and wildflowers for the sunken garden.

Anne asks good questions.

Personally I would be leery of roadside soil for growing food. Too many unknowns. I would be inclined to bring in soil I could trust.

Just an offbeat thought, but another option might be to contact the local university. There might be a doctoral student who is looking into roadside contamination of soil and water and has access to a lab.

I am also of the "But what nasties are in the soil?" camp solely because my brain goes to the worst case scenario when it comes to risk.

If you have a soil lab that can test the soil, that might give you better answers to balance your risk tolerance. The things I would be most worried about is vehicle based chemicals leaking into the soil (Oil, antifreeze, petro-chemicals) and an increase in sodium concentration from salt usage IF you are in those kinds of areas.

A picture may help evaluate the area, but you as a homeowner would also have better consideration on how the area has been used and what has been growing in that soil previously.

Thanks for the comments. I will err on the side of caution and not use the soil. The beds I already filled I will grow non-edible flowering plants that are shade tolerant instead of gingers and green leafies. I will see about an economically viable test for contaminats for those beds that are already filled.

The question then is: what should I do with the soil that I excavate? I don't exactly love the idea of throwing it away. But I am on a suburban lot. I don't really have anywhere to put it and my lot is planted principally with edibles, given the limited space.

If it's an old and well-travelled road, accumulated heavy metals like lead may also be a consideration. Remember leaded gasoline?

Douglas Alpenstock wrote:If it's an old and well-travelled road, accumulated heavy metals like lead may also be a consideration. Remember leaded gasoline?

The road is a major one for the neighborhood, but no through traffic. I suppose disposing of the soil is, sadly, the safest bet.

I was going to plant some native cocoplums in the swale next to the road. Rather than garden vegetables, I'd be eating fruit and seeds from a woody plant. What are the community thoughts on this. Sufficiently safe or still best to avoid? The swale is about 20' wide and then sidwalk and my front yard which has many fruit trees. I feel fine about that. But this conversation has increased my general toxicity paranoia! Maybe I will do some tests to clear my mind

You might consider myco remediation. Do your soil test. Grow mushrooms on n the soil, harvest and dispose of mushrooms. Perhaps do this in your now decorative beds too. Do a soil test. Improvements to an acceptable level? Grow food.

I have not done this. This guy from Fungi For the People sounds like he knows what he's doing. This link does not include the full experiment.

Joylynn Hardesty wrote:You might consider myco remediation. Do your soil test. Grow mushrooms on n the soil, harvest and dispose of mushrooms. Perhaps do this in your now decorative beds too. Do a soil test. Improvements to an acceptable level? Grow food.

I have not done this. This guy from Fungi For the People sounds like he knows what he's doing. This link does not include the full experiment.

Thanks. I heard paul discuss something similar to this on a recent podcast episode. It seems like a good idea. Thanks so much. And it works out at this bed is in a shade place (and is a hugel with a huge oak log in it).

Mike Benjamin wrote:

Douglas Alpenstock wrote:If it's an old and well-travelled road, accumulated heavy metals like lead may also be a consideration. Remember leaded gasoline?

The road is a major one for the neighborhood, but no through traffic. I suppose disposing of the soil is, sadly, the safest bet.

I was going to plant some native cocoplums in the swale next to the road. Rather than garden vegetables, I'd be eating fruit and seeds from a woody plant. What are the community thoughts on this. Sufficiently safe or still best to avoid? The swale is about 20' wide and then sidwalk and my front yard which has many fruit trees. I feel fine about that. But this conversation has increased my general toxicity paranoia! Maybe I will do some tests to clear my mind

Hey Mike, apologies,  I fear we are beating you down with worst case scenarios. CYA etc. We are speculating without hard data.

Unless you are in the runoff zone from a chemical dump site, I think planting woody shrubs that bear good fruit is an excellent plan. This is how we fix the world. My 2c.

hey there-- i grow in an urban area, we have a lot of fruit-bearing trees. i would not worry about it too much-- i might not grow leafy greens in soil that is iffy, but i think fruit would be fine. personally i'd take that soil and use it for composting/hugeling/worm farming, if i had the space. then after that, into the beds.
You mention summer tropicals- bananas are classic for growing in crappy soil and taking up rainwater. Mulberry, guava, strawberry guava would probably also do great.

Tereza Okava wrote:personally i'd take that soil and use it for composting/hugeling/worm farming, if i had the space. then after that, into the beds.

Thanks all. Tereza - can you clarify this point for me, as I'm highly interested. I get composting (add it to compost). I suppose for worm farming you would incorporate the soil into the bedding? And then after composted or processed through the worms, it would go into bed? But what about hugeling before going into beds?

sure!
to preface: i do bokashi in buckets. when the bucket is full, it has to be mixed with dirt for a few weeks to become fully broken down (at which point it's basically compost). I do that in a worm barrel, also throwing in whatever else i have around (rabbit bedding, stuff I've run through the chipper, etc). And by worm barrel I just mean a trash barrel with holes drilled in the sides and bottom, that never gets fully emptied and has an endless colony of worms in it. I don't ever fully empty it, they've probably developed their own civilization by now.
I usually try to have 1 part bokashi: 1 part dirt: 1 part extra roughage kind of stuff. The dirt I use is "bad"- spent dirt from planters, seed starting, etc, I usually have a few large pots that need to be disposed of. Any questionable dirt I have usually goes straight into that.


Occasionally I'm lazy and will just throw it in the garden in a trench, or just on the ground with some dirt over it (extra lazy option). But I occasionally will dig out a bed to add organic matter (hugelbed) and any questionable dirt will go in there, as it will all get broken down and improved.

Tereza Okava wrote:sure!
to preface: i do bokashi in buckets. when the bucket is full, it has to be mixed with dirt for a few weeks to become fully broken down (at which point it's basically compost). I do that in a worm barrel, also throwing in whatever else i have around (rabbit bedding, stuff I've run through the chipper, etc). And by worm barrel I just mean a trash barrel with holes drilled in the sides and bottom, that never gets fully emptied and has an endless colony of worms in it. I don't ever fully empty it, they've probably developed their own civilization by now.
I usually try to have 1 part bokashi: 1 part dirt: 1 part extra roughage kind of stuff. The dirt I use is "bad"- spent dirt from planters, seed starting, etc, I usually have a few large pots that need to be disposed of. Any questionable dirt I have usually goes straight into that.


Occasionally I'm lazy and will just throw it in the garden in a trench, or just on the ground with some dirt over it (extra lazy option). But I occasionally will dig out a bed to add organic matter (hugelbed) and any questionable dirt will go in there, as it will all get broken down and improved.

Thanks for sharing this. This is a good system for someone like me (i.e., lazy with lots of crap laying around tat I need to find something to do with, haha).

Plant bracken ferns and mushrooms along with wildflowers/flowers for a year or so until the soil has been cleaned up by the ferns and mushrooms.

This is at least of use for soil that you have to do something with.

Anne Miller wrote:Plant bracken ferns and mushrooms along with wildflowers/flowers for a year or so until the soil has been cleaned up by the ferns and mushrooms.

This is at least of use for soil that you have to do something with.

Thanks Anne. I will give it a go.