DC Urban Fruit Gardening with high lead levels? Container vs raised beds, etc?

Asked September 17, 2019, 3:00 PM EDT

Hello!

Since 2017 I've been creating a container garden (~30-35 gallon made-for-gardening and whiskey barrels and ~10 gallon large blue pots, plus ~8 gallon ceramic) because I had my soil checked in May 2017. I attached the results (they're also at the end of the note).

But the area that I garden in has tested for high lead levels (~1000ppm), not much arsenic, but some zinc (I don't know what the means?). Also ph is about 6.4. I haven't tested in 2 years.

  1. I put pine/hardwood bark chips and mulch over the entire back yard, except where's there is groundcover (ivy, vinca minor)
  2. I put all the vegetables and fruit trees in containers. I used ceramic pots, but this summer 2019, I added a bunch of larger half barrels, mostly for fruit trees. I bought the barrels at Home Depot
  3. I usually use filtered water from a hose (the kind that someone might use for an RV - Camco 40043).
  4. I also set up a small irrigation system (https://www.amazon.com/Irrigation-Garden-Distribution-Greenhouse-Automatic/dp/B07NM6RDB4/)

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My main question

Based on my test results (see below/photos), should I continue container gardening, or it okay to switch to raised beds for the fruit trees (and tomatoes/peppers/etc)?

What are your thoughts/opinions?
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Question #2

I've been reading online, that fruit and "fruit-like" veggies (tomatoes, peppers), don't generally transport lead/heavy metals to the fruiting part of the plant.

Is this generally true, but maybe not worth risking?

Or maybe I could plant a few fruit trees in the ground?


I've planted:
  • some fig trees
  • a pomegranate
  • a persimmon
  • concord grapes
  • blueberries
This fall, I am planning to also plant:
  • kiwis
  • PawPaws
  • maybe blackberries
  • maybe raspberries
  • more grapes
  • another persimmon
  • another pomegranate
(Currently all in larger containers - half barrels, large plastic pots. All the soil is from Home Depot certified OMRI, plus the Montgomery County LeafGro compost). I also have some Meyer lemons/citrus in the smaller plastic pots that I'll bring inside during the winter.

Since some fruits trees are barely in zone 7 (Asian Persimmons, Pomegranate, etc), the nursery said I need to mulch heavily to protect them in the winter. I was planning to essentially create raised beds around the barrels to protect the roots.

Or I would I want create raised beds (like 2-3 feet high) and replant the fruit trees (that I planted in containers this summer).

Since it's a "smaller" backyard area (~20'x15', away from the back of the house, south facing, 8-10 hours of sun over different parts, overlooking an alley that's located about 12' below the backyard), I'm putting everything closer together and just planning for all the different trees, annuals and vines to intertwine basically at some point.

I'm also planning to leave a portion in the very back open, so there'll always be enough sun for the berries, tomatoes, peppers. The fruit trees would be slightly further north.

Any thoughts/suggestions/ideas?

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Question #3

Is it okay to put a large barrel with grape vines close the back of the house, if there's a older painted extension (I didn't test that part of the soil, but it could have an underlayer of lead paint, not sure the year the extension was added), as well as a (probably) pre-2006 wooden porch?

Should I cover the container, so paint chips wouldn't fall in it, or is it not advisable to deal with?

I wanted to grow grape vines up the back of the house (and up the stairs to the porch), but am wondering about paint chips, as well as run-off from the treated-wood porch. The porch was painted red, but now is faded and there's green areas (I think from algae-like plants)

Any thoughts/suggestions/ideas?

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Question #4

My test results say that I need to increase Nitrogen content.

I've only really been adding mulch and wood chips - I realize that these are more carbon than nitrogen rich. I guess I could add more Nitrogen stuff like leaves and compost? Are there any recommended "organic" ways to increase N levels that you recommend?

I had a contained, plastic compost bin, but rats ate through the plastic, so I don't know if I can make own compost at the current time.

Also, the test results recommend to increase pH (from 6.3 to at least 6.5). I haven't done anything about because it seemed so close (0.2). I have been putting down some pine bark chips, which might decrease pH. Any "organic" suggestions?

  • Also, it says the P, Mg, Ca, and K values are too high. Is this a problem? And if so, how and why?
  • This test result said lead levels were ~730 ppm, not ~1000 ppm (from the other test). How would you recommend interpreting this?
  • And, what about using Azomite, and adding soil "probiotics" ?
  • In the containers, I've been adding a bit of Mikrobs - Microbial Plant Food, Dr. Earth Premium Gold All-Purpose fertilizer (4-4-4), and Azomite.

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Thanks very much!
D

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Heavy Metals Results
Sample ID (from Uof Delaware Ag extension) Lab No. Bag No. Date Received Date Completed
GARDEN BACK 26387 880703 5/18/17 6/27/17
Analyte Result
  • Soil pH 6.4
  • Arsenic (ppm) 4.4
  • Cadmium (ppm) 1.3
  • Chromium (ppm) 27.1
  • Copper (ppm) 31.3
  • Nickel (ppm) 9.7
  • Lead (ppm) 988.3
  • Zinc (ppm) 371.3
  • Analytical Methods: Soil pH - 1:1 (v:v) deionized water Heavy Metals: EPA3051 Digestion and ICP Analysis Note: Reporting units of ppm and mg/kg are equivalent for interpretation of results.

District of Columbia County District of Columbia soil testing vegetables heavy metals fruits

3 Responses

Hi, we’ll try to answer your questions in order.

Arsenic, cadmium, chromium, zinc, and nickel levels are all below the “Guidance Value Protective of Human Health”- http://cwmi.css.cornell.edu/Metals_Urban_Garden_Soils.pdf

Lead is trickier in your case. University of Maryland Extension, and many other institutions recommend not growing food crops in soils with soil lead levels >400ppm. This is based on a conservative interpretation of US EPA guidelines.

UME soil lead pub: https://extension.umd.edu/hgic/topics/lead-garden-soils

EPA guidance is more nuanced. See page 6 of this 2014 Technical Review:

https://semspub.epa.gov/work/HQ/174577.pdf

They show “potential risk” for soils in the 400-1200 ppm range and make suggestions for how to minimize exposure/ingestion risks (e.g., grow more fruiting crops which includes tomato and pepper).

Whether or not to move your crops into the existing soil is a judgement call on your part. Lead is a health risk mainly due to lead dust deposition on edible plant parts, shoes, clothing, hands, tools, etc. where it can easily be inhaled or ingested. If you maintain a 6.0 – 7.0 soil p, incorporate organic matter, minimize soil disturbance and keep soil covered, thoroughly wash crops, etc. you can greatly reduce your exposure risk. If children will be playing in the backyard you may want to be more prudent and keep your plants in containers.

It’s great that you want to maximize your backyard food garden. You will have healthier plants, less work, and more to eat if you give each plant the recommended space needed when it reaches maturity. For example you can plant small blueberry plants 1-2 ft. apart. But in a few years they will each need 15-20 sq. ft. of space to grow properly. Crowded plants become stressed and are then more susceptible to pest and disease problems.

If you keep fruit in containers it would be a good idea to bank insulating material around the containers over the winter.

We would recommend that you plant a flowering climber for the back of your house. A vigorous grape vine can cause structural damage to railings and sidings and stain wood with rotted fruit.

https://extension.umd.edu/hgic/topics/vines

https://extension.umd.edu/hgic/topics/native-plants

You can use high nitrogen fertilizers such as nitrate of soda, cottonseed meal, soybean meal, and blood meal to provide nitrogen without adding other unnecessary nutrients that are plentiful. LeafGro and other composts will provide a small amount of nitrogen. The soil test results show that the other major nutrients are excessive. These very high levels will not harm your plants. You simply do not have to add these nutrients.

Except for blueberry, which needs a 4.5 – 5.5 soil pH, all of your vegetable and fruit plants will grow well in a soil pH in the 6.0 – 7.0 range (6.5 would be ideal). Follow the soil test recommendations for liming (all liming materials are considered “organic.” The organic matter in your containers and soil provides the fuel for your soil microbes. No need to add probiotics of other soil amendments.

Jon

Thanks so much for all the great info!

I think I'll stick to containers and closed-bottom raised beds for the time being and then possibly re-evaluate in 2020.

In terms of spacing - hopefully everything will grow and then I can just move the containers farther apart, if need be.

I will add lime to the soil, but probably skip the nitrogen, since I won't growing anything in the soil, just in the containers.

Thanks and best wishes!