DC Urban Fruit Gardening with high lead levels? Container vs raised beds, etc?
- I put pine/hardwood bark chips and mulch over the entire back yard, except where's there is groundcover (ivy, vinca minor)
- 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
- I usually use filtered water from a hose (the kind that someone might use for an RV - Camco 40043).
- I also set up a small irrigation system (https://www.amazon.com/Irrigation-Garden-Distribution-Greenhouse-Automatic/dp/B07NM6RDB4/)
What are your thoughts/opinions?
- some fig trees
- a pomegranate
- a persimmon
- concord grapes
- maybe blackberries
- maybe raspberries
- more grapes
- another persimmon
- another pomegranate
- 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.
- 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
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:
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.
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.
Good luck and happy gardening!