Is the sawdust from composite decking safe for my herb garden?

June 4, 2015 7:25 AM

I'm currently having a deck installed in my backyard - yay! We're using composite decking made from recycled wood and high density polyethylene plastic. I noticed last night that they are cutting the boards quite close to my herb garden and the dirt and plants are covered in sawdust. Will this sawdust make my herbs/tomatoes unsafe to eat?

I called the company who makes the decking and the woman I spoke to said that the decking was made from the same materials as they use in their garden edging products . Since that's safe for vegetable gardening, she thought the sawdust would be okay in the garden and a good wash would be fine for the plants.

(Aside: Is it still called sawdust if it's not from 100% wood?)

Assuming that I'm going to carefully wash everything coming out of my garden and give everything a good soak to get the sawdust off of the plants before I pick anything, can I still harvest and use my basil, cilantro, chives and tomatoes? Or should I be digging up my recently-planted garden and starting fresh with new dirt and everything? (This seems really extreme so I don't want to do that if I don't have to.)

Any insight is appreciated. Thank you!

(I hoped I would never have to post my own 'Can I Eat This?' question, but here we are.)

posted by melissa to Home & Garden (7 answers total)

Best answer: HDPE is pretty safe and I can't imagine the exposure from a little sawdust is that big a deal. If you were an ultra purist you could start over but as far as I can tell from a quick review even the studies that demonstrate some leaching of endocrine disruptors from HDPE don't show a health affect, just that the chemicals are present. Here is an easy to read post on the various plastics that's actually got sources linked.
posted by Wretch729 at 7:55 AM on June 4, 2015

Best answer: If they're still working, cover the garden. My concern would be that the plastic dust is now in the soil, so even if you wash off the plants, they could take it up through the dirt. Is the decking treated with flame retardants? Formaldehyde is also pretty commonly used.
posted by three_red_balloons at 8:03 AM on June 4, 2015

Response by poster: Covering the plants makes sense, and I wish I had figured out to do it before they had started! :) I'm at work now and can't go back to cover my plants until after the builders are gone for the day. I figure two days worth of sawdust isn't much worse than one day so covering the plants now might be a case of too little, too late.

I am following up via email with the company who manufactures the composite material to get more information. Let's hope they respond. I hadn't considered other chemicals so now I'm feeling paranoid.

Will follow up if I get an answer from the company - any answers here are still very appreciated. Thanks!
posted by melissa at 8:29 AM on June 4, 2015

Best answer: Without knowing the company and exact product, it's hard to say what's in it. If it really is just pure polyethylene and wood, then it's very safe. Polyethylene is one of the most inoffensive plastics around.
posted by ryanrs at 8:43 AM on June 4, 2015 [3 favorites]

Best answer: Context: they make milk jugs out of HDPE. It's essentially long-chain wax.
posted by Huffy Puffy at 10:37 AM on June 4, 2015 [2 favorites]

Best answer: What you want to do is look at the MSDS (Material Safety Data Sheet) for you particular product, specifically the section on oral toxicity.

In this particular example, you can see this:

Oral toxicity (Rats):Practically non-toxic (LD50: greater than 2000mg/kg)

which is a pretty good sign that it's OK.

They also list out the components and the things that raise an eyebrow are marked "Trade Secret", which is why we look at the toxicity section. While neither HDPE or most woods are toxic, you need to wonder about the binders, dyes, etc.
posted by plinth at 11:28 AM on June 4, 2015

Response by poster: Follow up: I wrote the company and never heard back. We had a ton of rain so the worst of the sawdust was washed away, or deep enough in the dirt that there's no way I would have gotten it all out. I found the MSDS sheet online and it read as reasonably safe. I've been washing my herbs as I need them and no ill effects. Here's hoping any ill effects aren't slow ones. Thanks everyone for your insight.
posted by melissa at 10:52 AM on July 7, 2015