University of Maryland Extension

FAQs - Soil

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FAQs - Soil Testing

Other Soil FAQs
Can I add the ashes from my pellet stove to the soil in my vegetable garden?

How do I know that the top soil I purchased is any good?

All of my gardening books mention the term well-drained soil. What exactly does that mean and what can I do if my soil does not drain well?

What is the most efficient way to break up clay? We don't have access to compost.

I suspect that my soil may be contaminated with toxins. What can I do to get it tested before I plant a vegetable garden?

I am downsizing my vegetable garden this year and will be growing most of my plants in containers on my sunny deck. Is this a good idea and what is the best type of soil to use in the containers?

What is your opinion regarding roto-tilling a vegetable garden before  planting a winter crop of winter wheat? The plan is to till again in the spring. I have read that too much tilling disturbs the microorganisms in the soil.

How much organic matter is desirable? I am going to renovate my lawn. My soil test came back saying my soil contains 4.5 OM.

My soil test said to apply phosphorus to my vegetable garden, but doesn’t Maryland’s fertilizer law forbid phosphorus?

Can you help interpret soil test results?

I want to have the soil in my vegetable garden and lawn tested. Is it better to buy a pH meter or should I send a sample to a soil testing lab?

Can I add the ashes from my pellet stove to the soil in my vegetable garden?

Yes, the ashes from your pellet stove can be spread over the soil of your vegetable garden. Wood pellets are made from the sawdust of hardwood and softwood trees. Use the ashes in moderation as they can raise the pH of the soil making it too alkaline for vegetable crops.  Do not apply more than 20-50lbs. of ash to 1,000 square feet of garden area. Apply in the fall or winter and then incorporate it into the soil in the spring.  Dispose of excess ashes in the trash not in your compost bin.

How do I know that the top soil I purchased is any good?

Maryland does not have regulations that set standards for topsoil sales. Go to a reputable nursery or topsoil dealer and ask questions about where the soil comes from, what kind of soiling testing is performed, what the pH is and if anything has been added to it. Examine the soil before purchasing it. Topsoil should be dark and crumbly with an earthy smell. Do not purchase if the soil is foul smelling, has grayish mottling or a chalky texture. Some sellers have a mix of topsoil and leaf compost which can make an excellent growing media for raised beds.

All of my gardening books mention the term well-drained soil. What exactly does that mean and what can I do if my soil does not drain well?

Well-drained soil is a commonly encountered gardening term as this is a requirement for most of the plants we grow for optimum growth. The term means simply: soil that water quickly penetrates through. Poorly drained soils are often clay, in low-laying areas or very compacted. Sites that slope can also be poorly drained if the water does not penetrate the soil but merely runs down the hill. Poorly drained soils make root growth difficult and the plants die. Drainage can be improved by adding organic matter or planting in raised beds. Sometimes the easiest solution is selecting plants that can tolerate ‘wet feet’. There are many to choose from.

What is the most efficient way to break up clay? We don't have access to compost.

It would help to know the ultimate purpose of the area to be loosened. For example, if it is a lawn area, it may be adequate to use a core aerator. If the area is to be used as a garden, it may require deep tilling or the use of a broadfork or a garden fork. In either case, it would be extremely beneficial if you could incorporate some organic matter into the loosened soil. You do have access to compost in your area whether it be bagged or in bulk. Leafgro is a reliable compost that is available in most home stores, garden centers, and nurseries.

I suspect that my soil may be contaminated with toxins. What can I do to get it tested before I plant a vegetable garden?

The regional soil testing labs we have listed on our website test for basic soil chemistry including soil pH, phosphorus, potassium, calcium and magnesium. Some will test for lead for an additional cost.If you want soil tested for other heavy metals and contaminants you would have to contact a private soil testing lab that does this type of testing.  You need to know what you want the soil tested for. This type of testing is expensive. To find a private testing lab search the internet for “‘Environmental Testing Services in Maryland” or “Analytical Services in Maryland”.

I am downsizing my vegetable garden this year and will be growing most of my plants in containers on my sunny deck. Is this a good idea and what is the best type of soil to use in the containers?

Yes, many folks successfully grow their vegetables in containers.  A number of commercially available bags of potting media referred to as ‘soil-less potting mixtures’ are on the market. They are sterile, reducing the risk of introducing soil pathogens and are usually comprised of peat moss, vermiculite, and perlite. They can be used straight from the bag or mixed with 1/3rd to ½ half compost. Containers can dry out quickly and watering them twice daily may be necessary during periods of hot, dry weather. Apply water until it runs out the drainage holes.  Fertilize plants with a water-soluble fertilizer according to label directions. Fish emulsion and sea kelp are organic types of water soluble fertilizer. Slow-release fertilizer pellets also work very well in containers, use at the lowest recommended rate.

What is your opinion regarding roto-tilling a vegetable garden before  planting a winter crop of winter wheat? The plan is to till again in the spring. I have read that too much tilling disturbs the microorganisms in the soil.

The benefits of the cover crop far outweigh the temporary disturbance caused by tilling. To avoid damaging the soil structure do not till if the soil is too wet. Plant the cover crop now and then mow it down in early spring (early April). Allow the cut wheat to lie on the ground for the rest of the month. Then till the rotting plant debris into the soil in early May, prior to planting around Mother’s Day. Or you can skip the spring roto-tilling and plant right through the decaying vegetation. Planting cover crops and incorporating additional organic matter into the soil each year can help encourage soil microorganisms. 

How much organic matter is desirable? I am going to renovate my lawn. My soil test came back saying my soil contains 4.5 OM.

Organic matter is the end product of the decay process of plant or animal residues.  Soils with an adequate percentage of OM retain more moisture, have a crumbly structure that reduces soil compaction and contain a reservoir of nutrients that are slowly released over time.  Soils with 3%-5% OM are sufficient, so don’t add any compost.  Continue to let your grassclippings decompose on your lawn and in the fall do not rake and remove your fallen leaves. Finely chop them up and allow them to naturally break down. Both of these practices will help to maintain the organic matter in your soil with little effort on your part. 

My soil test said to apply phosphorus to my vegetable garden, but doesn’t Maryland’s fertilizer law forbid phosphorus?

Not at all...that law is for lawns!  The new law came about because excess phosphorus and nitrogen create dead zones in the Chesapeake Bay, killing crabs and other aquatic plants and animals. While nitrogen is good for lawns when applied in the fall in the proper amount, phosphorus needn’t be applied each year. This law doesn’t apply to vegetable garden, because vegetable crops have different needs than a lawn. You’ll be able to find garden fertilizers containing phosphorus as usual, especially at stores that cater to backyard vegetable growers. 

Can you help interpret soil test results?

Yes! The best way for us to help is for you to contact us through "Ask the Experts".  Our certified professional horticulturists can assist you. If possible, take digital photos of the results and attach them to your question.  Otherwise, provide detailed information of your results. 

I want to have the soil in my vegetable garden and lawn tested. Is it better to buy a pH meter or should I send a sample to a soil testing lab?

Our advice would be is to send your samples to a soil test lab.  We do not recommend home test kits or pH meters for a number of reasons.  pH meters can become unreliable if they are not calibrated properly.  Soil test labs also provide important information such as phosphate, potassium and magnesium levels in addition to the pH of your soil.  If necessary, liming and fertilizer recommendations are also provided.  Many labs, usually for an additional fee, test the organic matter of the soil or for lead. Testing for lead is important if you are growing vegetables.  Lawn and garden soils should be tested every 3-4 years to make adjustments based on recommendations provided by your soil test results.  

Please send us a question at Ask the Experts if you have a soil question you would like answered. Digitial photos can be attached to your question.

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