Assess lawn health before fertilizing

Adequate soil nutrition is necessary for a healthy lawn and garden. But because fertilizers are relatively cheap, many people are tempted to pour it on, without regard to whether the plants really need it.

Nitrogen, especially, is often over-used, at least in part because it produces quick and lush growth. That's not always a good thing, however. Too much nitrogen will discourage flowering and vegetable production in favor of leaf growth. This lush new growth also is a prime target for chewing or sap-sucking insects such as aphids.

Excessive nitrogen can "burn" plants and damage leaves by increasing the mineral salt concentration in the soil. Even worse is the fact that excess nitrogen, especially on lawns, results in runoff that damages streams or leaches into groundwater. Water with high levels of nitrate is considered unsafe to drink. So you might want to consider cutting back on the lawn fertilizer, or at least use the slow-release kind.

How should we safely and effectively approach the job of fertilizing our gardens? First, have a soil test done every couple of years to measure your soil's health and nutrient status. While you can buy a soil test kit from your garden center, I recommend a full-spectrum test to use as a baseline. This will include an assessment of organic matter and micro-organisms, and requires a professional test. For a list of places to get a full-spectrum test, contact the OSU Master Gardener Plant Clinic at 541-776-7371. In addition, observe earthworm activity, how prone your soil is to compaction, and how well it drains, all of which are indicators of soil health.

Two nutrients other than nitrogen also need to be addressed, because they usually come packaged together with the nitrogen, which is noted by the "N" on the fertilizer package showing NPK.

The "P" stands for phosphorus, which is vital for flowering and fruiting capability and tissue strength and helps plants absorb micronutrients. Plants with slow growth, stunted and disfigured leaves, or leaf drop may have a phosphorus deficiency.

Potassium, indicated by the letter "K," is vital for healthy roots and immune system. It contributes to the overall health and vigor of plants.

A way to remember the importance of the above nutrients is to think "up" (nitrogen for the top of plant), "down" (phosphorus for good roots) "and all around" (potassium for overall plant health).

NPK numbers are listed on fertilizer packaging. For example,10-20-10 indicates a higher amount of phosphorus, while 21-0-0 is high in nitrogen, and 13-13-13 is a balanced fertilizer. A soil test will help you know what you need.

Organic fertilizers such as manure feed plants in a slow, steady fashion and add organic matter to your soil.

Chemical fertilizers can be compared to having a cup of super-caffeinated coffee for breakfast instead of something healthful to eat — it may give you a kick start, but doesn't have staying power.

Coming up: Ready-Set-Grow, a day for beginners, will be held Saturday, March 16, at the Southern Oregon Research and Extension Center, 569 Hanley Road in Central Point. The day features four consecutive classes: seed starting, vegetable gardening, annuals and perennials, and Rogue Valley soil and water. Classes begin at 8:30 a.m. The cost is $5 each or $15 for all four. Call 541-776-7371 to register.

Carol Oneal is a past president of the OSU Jackson County Master Gardeners Association. Email her at

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