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Elisabeth C. Miller Library

Keyword: Soil testing

Safety of gardening in arsenic-affected surfaces

This is about composting from raised beds constructed of railroad ties. I went to a workshop on growing edible plants, and was informed that one cannot eat anything grown in a railroad tie bed because of arsenic and other nasties, and if one has such beds, they should ONLY BE USED for ornamentals.

I try to compost everything in my garden, so I need to know if it is safe to use compost made from plants growing in railroad beds on the beds where I am growing edibles. If it is not safe, would time, weather, or decomposition EVER make it safe? I’m willing from now on to put all the soil-contaminated clippings in the city yard waste bin that goes to Cedar Grove, but I’d rather be able to make use of them in my own garden.

 

Your question about the safety of compost made from plant matter grown in a railroad-tie bed is complex. Railroad ties are treated with wood preservative that contains arsenic. Arsenic never goes away entirely, but the amount may be at lower levels than Washington State’s law on clean-up, based on parts-per-million. I would definitely recommend a soil test. Here is information from the Northwest Coalition for Alternatives to Pesticides, which has a page on chromated copper arsenate.

The Center for Disease Control has published a Public Health Statement on arsenic, excerpted below:
“About 90% of all arsenic produced is used as a preservative for wood to make it resistant to rotting and decay. The preservative is copper chromated arsenate (CCA) and the treated wood is referred to as ‘pressure-treated.’

Arsenic cannot be destroyed in the environment. It can only change its form, or become attached to or separated from particles. It may change its form by reacting with oxygen or other molecules present in air, water, or soil, or by the action of bacteria that live in soil or sediment. Arsenic released from power plants and other combustion processes is usually attached to very small particles. Arsenic contained in wind-borne soil is generally found in larger particles. These particles settle to the ground or are washed out of the air by rain. Arsenic that is attached to very small particles may stay in the air for many days and travel long distances. Many common arsenic compounds can dissolve in water. Thus, arsenic can get into lakes, rivers, or underground water by dissolving in rain or snow or through the discharge of industrial wastes. Some of the arsenic will stick to particles in the water or sediment on the bottom of lakes or rivers, and some will be carried along by the water. Ultimately, most arsenic ends up in the soil or sediment. Although some fish and shellfish take in arsenic, which may build up in tissues, most of this arsenic is in an organic form called arsenobetaine (commonly called ‘fish arsenic’) that is much less harmful.”

Washington State University has information on gardening on arsenic- or lead-affected soil which may be of interest to you.

To be cautious, you should keep the compost from these beds separate from your other compost, and only use it on your ornamental plants already being grown in those beds. I don’t recommend putting even slightly arsenic-contaminated yard waste into the city compost, since that means the problem is being spread farther afield. It would be worthwhile testing every so often for soil contaminants. Here is King County Public Health’s guide on arsenic, and testing information.

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Katsura trees’ soil needs

I have some dying Katsura trees. I created a dry stream to one side of them to redirect water (they don’t like wet roots). The owner has put 1-2 inches compost/soil down for some good nutrition and a few tree stakes into the area. There is also landscape fabric (the gray kind rain can get through) and another inch of bark to stop a horsetail problem that creeps in every year.

I am wondering if the the soil around the tree roots has become compacted by rains and is prohibiting the trees from getting oxygen through their roots. The yellow is not in leaf veins like an iron deficiency usually looks; it is almost as if the plant is getting its chlorophyll drained from inside. No bugs present to my knowledge either. I would like to know both what I might do about the soil and about the trees.

Some solutions to the problem may be to take some dead branches or stems to a Master Gardener clinic and ask them to help you identify what could be happening. You may also want to check that the compost is not closer than 4 inches from the trunk of the trees. If it is, scrape it away. For further evaluation of the soil, take a sample from around the tree and send it to a lab for analysis. Our website has a Soil Testing Information section that includes a list of labs that do soil test analysis. Check the area for drainage by digging a hole and filling it with water or let the rain do it and then see how long it takes to drain away. Perhaps you have a layer of hardpan clay underneath the trees that is blocking the drainage in winter and preventing the water from getting to the roots in summer.

A great resource on Katsura trees (Cercidiphyllum japonicum) is Dirr’s Hardy Trees and Shrubs: An Illustrated Encyclopedia by Michael A. Dirr. The author notes that the tree requires ample moisture in the early years of establishment. From the book, Trees and Shrubs for Pacific Northwest Gardens, by John A. Grant and Carol L. Grant, Katsura trees prefer deep soils and adequate summer moisture. There is a Katsura planted in the Arboretum on the edge of a pond in soil that is permanently wet and it is doing just fine.

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alkaline and saline soils

Can you tell me how alkaline soils are formed and if and how they are related to saline soils?

 

Saline soil may have a high pH, a characteristic shared with soils which are alkaline. You may find this information on soils and pH useful:

Diagnosing Saline and Sodic Soil Problems

Plant Materials for Saline-Alkaline Soils

Soil pH: What it Means

  • Alkaline soil: A soil whose reaction is greater than pH 7.
  • Acid soil: A soil whose reaction is less than pH 7.
  • Saline soil has a pH less than 8.5.

Saline soil, as defined in Soils: An Introduction, by Michael Singer and Donald Munns (Prentice Hall, 1999): “Saline soils …contain large amounts of soluble salts, appreciably more soluble than calcium sulfate. Most commonly, these are salts of Na, Ca, and Mg, with chloride, sulfate, and bicarbonate…soils are considered saline if their electrical conductivity exceeds 4 deciSiemens meter-1. Many plants suffer at this level.”

To answer your question about how alkaline soils are formed, here is what Clemson University Extension says:
“The pH value of a soil is influenced by the kinds of parent materials from which the soil was formed. Soils developed from basic rocks generally have higher pH values than those formed from acid rocks.”

Rainfall also affects soil pH. Water passing through the soil leaches basic nutrients such as calcium and magnesium from the soil. They are replaced by acidic elements such as aluminum and iron. For this reason, soils formed under high rainfall conditions are more acidic than those formed under arid (dry) conditions.

Application of fertilizers containing ammonium or urea speeds up the rate at which acidity develops. The decomposition of organic matter also adds to soil acidity.

best base soil for raised bed organic gardening

I recently moved to a new house that had what looked like a fair amount of chemicals dumped on the land around it. What do you recommend as a base soil for raised beds for organic gardening if you do not want to trust what you have?

The first thing you might consider doing is having your soil tested. There are various labs that can test for toxins as well as for soil type and nutrient deficits. Here is a link to a WSU site, which lists the labs and what they do. These labs primarily serve agriculture, so you might consider getting a soil test from a lab that specializes in home gardens, such as University of Massachusetts, Amherst. Also, if you suspect heavy metals in the soil, there is a link from Seattle-King County Public Health to labs that will test for toxins.

In her book, Backyard Bounty (New Society Publishers, 2011), British Columbia gardening expert Linda Gilkeson says that for your raised bed (or any situation where there was either no native soil, or where you are replacing the existing soil) you should “buy the best soil available, and mix in a generous amount of compost, leaf mold (well-rotted leaves) and other organic matter as you fill (1 or 2 parts compost to 9 parts soil).”

If you purchase topsoil, make sure to find out what the composition of the topsoil is. Linda Chalker-Scott’s factsheet from Washington State University Extension indicates that the ideal percentage of organic matter [abbreviated as OM] in topsoil used for gardens is 5% by weight.

Excerpt from the WSU blog discussion of this topic:
“If you’re purchasing topsoil, check out what you will be getting before it’s delivered. Ask the seller what the topsoil contains and also ask for the producer’s test data regarding pH, salt level, nutrient levels, OM content, and texture. If they don’t have that data available, you may want to consider taking a sample and have it tested yourself. Also, find out if the soil has been screened to remove rocks. Before you’re stuck with unsuitable topsoil, know exactly what you’re getting.
Garden Hint: Topsoil is usually sold by the cubic yard. One cubic yard of soil will cover about 50 square feet to a depth of four to six inches.”

optimal pH for Prunus lusitanica

Some of my Prunus lusitanica (Portugal laurel) shrubs are changing the color of the foliage and stems. Normally the leaves should be dark green and the stems are a dark cranberry red. The soil here at the coast is very sandy. I have put composted manure (the type from bags), fertilized them, and added a bit of lime to the soil around the trunk and close to the root zone. I have not seen much of a response. Do you know what is the optimal pH for Prunus lusitanica? I am concerned about these shrubs because I just planted them last summer.

 

Prunus lusitanica tolerates a wide variety of pH and moisture levels in soils. See California Department of Forestry SelecTree webpage about this plant.

According to the webpage of a local Seattle garden writer, the leaves do change color slightly, acquiring a bluish tinge in late fall to winter. She also says that Prunus lusitanica does not like wet feet.

What colors are the leaves turning? You might consider testing the soil, to make sure things are not out of balance. Here is a link to the Miller Library website’s links about soil testing.

Is it possible that the bagged manure was still hot, that is, not fully aged? If so, that could cause problems.

You might also bring in photographs or sample leaves to a Master Gardener Clinic for diagnosis. You can locate a Master Gardener Clinic within Washington State at this website.

on testing vegetable garden soil

I would like to know if there is some place where I can have my vegetable garden soil tested. For the last two years my vegetable plants were abysmal except for tomatoes and lettuce.

 

The Natural Lawn & Garden Hotline, sponsored by Seattle Public Utilities, provides the following recommendations on how to take a soil sample:

1) Take about 10 vertical slices of soil from the top 6-8 inches of your garden bed. If there is an area that you suspect to have problems, test this soil separately.

2) Place soil slices in a plastic bag and mix thoroughly. You are getting the average of the soil in your garden bed.

3) Take 1 cup from this mixture and dry it at room temperature. Do not dry in oven, on radiator or in microwave!

4) Put dry soil sample into a Ziploc bag and seal.

5) Label the outside of the Ziploc bag.

6) Mail to one of the soil testing labs below with completed order form and payment.

A WSU has a publication on soil testing for vegetable crops but it is mainly for agricultural growers.

Another option is the University of Massachusetts, Amherst soil testing laboratory.

This page has information and forms to send in with your samples.

For testing of toxics see:
King County’s Resident Self-Testing Page.

A & L Western Laboratories, Inc. in Portland, OR can provide soil and plant analysis.

Garden Tip #98

Test your soil for Ph and nutrients before your next planting project. Our county extension service no longer tests soil. Soils and Soil Testing Information from the Miller Library has a list of places to send samples and how to collect them.

After you have your soil test analysis with its recommendations for 200 pounds of nitrogen per acre, use these handy conversion tables to convert that to your 100 square foot P-patch. Fifty other tables and formulas will help you convert just about anything you might need for the garden, including how much potting soil you will need to fill those 10″ flower pots. Conversion Tables, Formulas and Suggested Guidelines for Horticultural Use from the Cooperative Extension Service, University of Georgia College of Agricultural and Environmental Sciences.