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These concepts help a healthy garden grow

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Thursday, May 15, 2008

Now that planting time has arrived for many of our vegetables, I am receiving a great number of questions on soil preparation, amendments and mulches. Some so-called "topsoils," sold in bags or in bulk, may have undesirable ingredients for a vegetable garden. Here is a sample of some questions and, in my response, some concepts you may want to consider before you use certain soil amendments or products.

Q. Is dyed-black mulch toxic and therefore not to be used in a vegetable garden, or is it safe?
-- Joseph P., Roselle Park

A. If you mean black plastic mulch, then the answer is yes, it is safe to use in the vegetable garden. There are a variety of plastic mulch colors that are used commonly in vegetable gardens and commercial farms. Colors include black, red, green, blue, white and brown. You can buy plastic mulches from many garden centers or use heavy-duty garbage bags around plants to reduce weeds and help retain moisture.

When using garbage bags, cut open on one side and at the bottom for a single layer. Lay plastic down before planting. Secure ends of the plastic by burying 2 to 3 inches of outside edges under the soil. With a utility knife, cut a small hole or X where you will place plants.

Plastic mulches are commonly used for tomato, pepper, eggplant, cucumbers and melons to reduce weeds between these large plants. For many other vegetables and for areas of the garden where you will practice succession plantings, as with lettuce, carrots, radish, spinach and peas, it is not wise to use plastic within the row due to tight spacing and the need to rework and replant the same season.

Some gardeners use landscape fabrics in garden paths and cover with organic mulches to help prevent weeds.

As for organic mulches, they are rarely black in color. Some bark mulches can be dark in color, but bark mulches are not the best mulches to use around vegetables. Bark mulches could be used in permanent pathways, but should be kept away from production areas. If wood mulches mix in with the soil around roots, the mulches will rob nitrogen from surrounding vegetable plants as soil microorganisms begin to break down noncomposted organic materials.

Q. I have two large dogs that generate a lot of waste. Instead of dumping the waste in the garbage, I was intending to dump it in the two vegetable gardens I have in the backyard as fertilizer. My wife tells me that this would destroy anything growing there. I have not used the garden for six years or more, except to store chopped up leaves in it each fall. Is there anything I should add or do before tilling the dirt and adding vegetable seeds? Will the dog waste cause any problems?
-- Fulton H., Martinsville

A. I do not recommend using pet waste in the vegetable garden. There are an assortment of disease organisms that may present problems to people if the waste is not properly treated or composted. Strains of harmful E. coli can survive in waste products. This can especially be a problem in areas where you are growing leafy vegetables, root crops or where vegetables or fruits are touching the soil.

The only waste I would recommend using in a garden is dehydrated and composted cow or horse manure that has been properly treated to reduce pathogens.

I recommend that you mix 3 inches of peat moss or leaf compost into the topsoil. Use some of that soil as a mulch around nonedible ornamental plants and incorporate into ornamental plant beds to improve those soils. Then go back in and add more organic matter to the remaining diluted soil and grow only tomatoes, peppers or caged vegetables that produce fruit away from the soil layer.

By next year, repeat the same practice by adding leaf compost or peat moss into the top 12 inches of soil. For this year, grow leafy vegetables such as lettuce in other areas or in containers, and give the waste and potentially harmful bacteria time to break down.

Q. Last year, I added a black topsoil to my vegetable garden and had problems with my tomatoes, peppers and squash. They struggled the whole season, turned yellow and eventually, some of the plants died. What should I do?
-- John S., Red Bank

A. There are several things to consider in this scenario. If many of the plants were yellow, especially in the older leaves, the problem could be that the soil was not simply soil but contained noncomposted organic ingredients. Organic components like food waste, bark or leaves, if incorporated around roots, can rob plants of nitrogen as soil microorganisms break down the organic materials. Unfortunately, some soil products could have some of these organic materials as a prime contaminant in the mix.

Quality topsoil is normally not black in color. If the soil is very dark in color, smell the product to determine if there is an ammonia or other foul odor. If the product has an odor, then I would avoid using this in your vegetable garden. Some products may have undesirable organic contaminants or even sewage sludge. It is sometimes very difficult to find quality topsoil unless you have a reliable source.

In many cases, I would recommend improving the soil that you have with peat moss or finished compost. For now, you could add some additional nitrogen to the garden with dried and composted cow manure, blood meal, kelp products or standard garden fertilizer at desired levels based on soil tests. Mix organic materials such as finished compost or peat moss into the top 12 inches of soil. Grow vegetables on raised, dome-shaped beds if possible, to allow for good drainage and air circulation. If you follow these recommendations, you should have a healthy garden this year.