Gardening with Chip

Adding organic matter to gardens

Organic matter is a valuable addition to all gardens. It improves soil textures and adds nutrient holding capacity to the soil. The stimulation of biological life as the material breaks down can reduce disease problems.

However, adding organic matter can tie up nitrogen for some time. This can hurt plant growth, especially annual flowers and vegetables. The degree of tie-up relates to the relative amounts of humus and un-decomposed residues in the material. If the material has completely composted, there is almost no tie-up. If the material is mostly "raw,” the tie-up can be substantial.

The way around the problem is to add extra nitrogen to feed the decomposer organisms. A standard recommendation is to add 3 pounds of actual nitrogen for each cubic yard of organic matter. This is in addition to the fertilizer needed for the crop itself.

So how do you figure how much to add? If you use a synthetic source of nitrogen like urea (46-0-0) or ammonium sulfate (21-0-0), calculate the extra N based on the percentages in the material. For ammonium sulfate, that would be 3/.21 = 14 pounds. Urea would be 3/.46 = 6.5 pounds. If you use an organic fertilizer like Biogro, it has about seven percent N; thus, you need 3/.07 = 43 pounds of the fertilizer.

Remember, these amounts are in addition to the fertilizer you planned to apply to feed your vegetables or flowers. For more information, visit extension.oregonstate.edu/news/add-organic-matter-improve-most-garden-soils.

We also have a great publication called Fertilizing Home Gardens available from our office or on-line at extension.oregonstate.edu/catalog/ec-1503-fertilizing-your-garden-vegetables-fruits-ornamentals.

Buying topsoil

The following is adapted from an article by retired OSU Soils Specialist John Hart:

When you buy topsoil, make sure you know what you are buying. Since there's no legal definition of 'topsoil,' you could be getting just about anything. People think that 'topsoil' is better than other soil because it contains more organic material, but it isn't necessarily so. Topsoil is just surface soil. That's all you can claim about it. It isn't always good material for home gardens.

Don't buy any loads of topsoil sight unseen. Go to the location where the topsoil is stored and investigate.

If an on-site inspection isn't possible, inspect the load in the truck before it is dumped into your yard. Topsoil shoppers should keep the following information in mind: Just because something is sold as "topsoil," it isn't necessarily of desirable soil texture. Topsoil can range from clayey to sandy material. The best texture for gardening is loam - or sandy loam - with fairly equal proportions of sand, silt and clay.

To estimate the amount of sand or clay in a batch of topsoil, take along a small container of water. Mix some of the soil you're considering buying with water. Make a mixture with bread dough consistency. If the soil forms a sticky mass, there's too much clay. If it feels gritty and watery, there's too much sand. Good garden loam should not feel very sticky. Take a handful of damp topsoil and squeeze it in your fist. If it is loam, it will form a ball that easily breaks apart.

If you do not find exactly the right soil, modify it with compost. Addition of organic material will increase its water holding capacity, make the soil easier to work up for planting and make it more hospitable to plant roots. You can add sand to soils, but only if you are adding an equal volume of organic matter at the same time. For example, if you wanted to add four inches of sand, also add four inches of compost at the same time. If you don’t do that, you risk making a low-grade concrete out of your clay.

It is not unusual to bring some nasty weeds in with the topsoil. Of particular concern is horsetail or equisetum. It is helpful to look at the soil prior to purchase with an eye to the weeds that are present at the time or the remains of weeds from the previous season. Topsoil is usually sold by volume, in cubic yard units. When ordering or buying topsoil, a good rule of thumb is to remember that one cubic yard of topsoil will cover about 50 square feet of garden to a depth of about four to six inches.

Take excess produce to the food bank, senior centers, or community meals programs. Cash donations to buy food for the food banks are also greatly appreciated. This is especially true now, since many of the federal food funds that helped the food banks have been cut hard. Sign up for gardener training in either county.

Very helpful information sources are your local Extension offices. The Columbia County Extension is 503-397-3462, the Wahkiakum County Extension is 360-795-3278, and the Cowlitz County Extension is 360-577-3014. The Extension Service offices offer their programs and materials equally to all people.

Advice on future garden topics is always welcome by emailing me at chip.bubl@oregonstate.edu.