Dear Dirt Nerd,
I’ve just purchased a house and can now fulfill my highly idealized goal of growing food for my family. Maybe a good future topic to discuss would be: to raise a garden bed or not? And toxins like lead and arsenic in the soil. As a new gardener with kids, I wonder often about whether it’s all hoopla or not.
Thanks for listening,
I am all for people starting their urban farmsteading dreams with one garden bed. And that garden bed, without exception, should be raised.
Growing at ground level in New Orleans is extremely hard work. Our standard issue soil, like most urban soils, is very compacted, and it also has heavy clay content, making that compaction even more dense. But your yard has soft, even sandy dirt, does it? That’s probably because your house, or your lot, or whatever it is you’re growing on, was affected by Hurricane Katrina once upon a time, underwent demolition and/or renovation, and was covered with fill dirt after the fact, which tends to be comprised mostly of sandy silt pulled from the Mississippi River. It is not standard issue. Sandy soil is as hard to grow in as compacted or clay soil. Sandy soil holds very little water or nutrients, and compacted soil doesn’t allow water or roots to pass through. Food plants, pretty much across the board, cannot live happy lives like this. They need a comfortable in-between, namely loam: 40% sand, 40% silt, %20 clay, or somewhere thereabouts.
Amending your soil with compost, fertilizers, fresh topsoil, soil conditioner, or whatever else you can get your hands on can ameliorate this situation with time, effort, and money, but the issues with growing food in the ground do not end with soil quality. Our dirt is also riddled with weed seeds. Every time you mess with it you will stir up a new horde of untold horrors that will combat your veggies until you rip them all up and till the soil again, bringing forth another wave of beasts. It does not end. With raised beds and fresh soil, you will still have to battle these unconquerable beasts, but their stranglehold will be singlehanded and your vegetables will be left room to breathe.
The other major non-toxic reason for building raised beds is our altitude and climate. That is to say, it floods here a lot. Giving plants even a few inches of height over ground level can significantly improve their health. Of course, plants love water as all carbon-based life forms do, but most of them can’t abide living in it. When soils are saturated with water over long periods of time, plant roots essentially drown. They cannot breathe; they become anaerobic. Nasty bacteria can take hold and things go downhill fast from there.
Raised beds are good for controlling your little garden ecosystem beyond soil quality, weeds, and water issues. Having a contained space nominally separated from the rest of your yard gives you more control over all the little things that make growing food work. This is partially just aesthetic, but truly, having a well-defined space apart from and above whatever else your yard may be doing draws the eye and the mind to details you may miss in your food garden if it is co-mingling with “nature” or whatever.
Now on to the juicy bits. The cancer-causing, brain-destroying, violence-inducing, juicy, juicy bits. New Orleans dirt is rife with lead and arsenic, a very serious problem that deserves far more attention from the local and federal government than it receives. I would strongly recommend that anybody with children get their soil tested for lead through the LSU extension service (lsuagcenter.com/soil), because if you’ve got lead in your dirt, your kids should not be playing in your yard. That said, growing food in lead-ridden soil is not absolutely terrible. That said, you still shouldn’t do it.
If you have moderate to high levels of lead in your soil, go ahead and build a raised bed garden. By and large, food plants do not uptake heavy metals in detectable levels when they are planted in toxic soils. What’s more, what little bit they do take in does not easily transfer into your body if you consume such a vegetable because of chemical bonds that I haven’t understood since high school. Also, when plants do uptake lead or arsenic they hold the toxins in their stalks and leaves, not in their fruits, not even a little bit. So if you’re growing citrus, tomatoes, peppers, or green beans—or anything at all that isn’t leafy—then you are absolutely safe from lead, almost without exception.
The real danger in leaded soil is loose dirt, or the tiny dust particulate that will get your children when they play in the dirt. It is the dirt stuck to the outside of your plants that holds lead in dangerous quantities, not the lead that plants may have leached from the soil. This is why I say you are safe with fruiting plants almost without exception, because any sheen of dirt over them can contain lead. If you know there’s lead in your soil, wash your vegetables thoroughly. Do not consider growing root vegetables in even mildly toxic soil. While your carrots or beets will be safe on the inside, all those little nooks and crannies on the outside of the plant will inevitably hold soil, no matter how hard you rinse them.
Greens can be similarly laden with uncleanable dirt holes, and should be grown with caution. Also, a few greens and other plants, notably mustard greens, are “hyperaccumulators,” or plants that are exceptionally good at leaching heavy metals from soils. They are used effectively to clean toxic soils, and for this reason should never be grown for food in dirty dirt.
In conclusion, lead is dangerous, but not particularly dangerous to grow food in, but grow food in raised beds anyway because if you don’t, you may never grow food again—not because you died of lead poisoning, but because your garden died along with your will to try again.
Questions or news about gardening? Email the Dirt Nerd at email@example.com