Gardening with Allen: Apply fertilizer to help out lawn - The Columbian

Allen Wilson is a Vancouver gardening specialist. Email Allen Wilson at allenw98663@yahoo.com. Photo

My lawn has not come through this hot, dry summer very well. Is now a good time to fertilize?

Lawns will naturally start looking better soon as they respond to the fall rains. Fertilizer right now will make them look even better. By late October or November grass is green but stops growing. Fertilizing in October increases the green color without stimulating growth. It also keeps the lawn greener during the winter.

Root growth is still very active, so grass plants take up the fertilizer, especially nitrogen. The nitrogen is used to make amino acids which are stored in the roots and crown. The amino acids are available for early spring growth before roots can actively take up nitrogen.

The three major fertilizer ingredients are nitrogen, phosphorus and potassium. Nitrogen is the most important for leaf growth so most lawn fertilizers contain 15 to 25 percent nitrogen. According to Washington law, there is no phosphorus in lawn fertilizers. Most brands of lawn fertilizer have a fall blend, which contains about half as much potassium as nitrogen for better winter growth. Iron is another nutrient which is important for lawn growth and dark color. Only small amounts as low as 1 or 2 percent are adequate.

Because of heavy rainfall, Northwest soils are quite acid. Lawns will benefit from a yearly application of lime or similar soil-sweetening products that contain calcium. Up to 5 pounds per 1,000 square feet can be applied. Rhododendron, azalea, camellia, heather, mountain laurel, magnolia, holly, dogwood, andromeda, leucothoe, blueberry and raspberry prefer acid soil and should not be treated with lime.

If you have some broadleaf weeds in your lawn, now is the best time of year to control them. Plants are actively sending food made by the leaves to the roots for root growth and storage. The herbicide piggybacks on that natural movement and is transferred to the roots, which quickly kills the whole plant. If you have quite a few weeds scattered throughout your lawn, your best choice is a weed-and-feed product. If you have only a few weeds a liquid weed killer or hand digging is a better choice.

I like to mow the lawn short one time about the time fall rain starts. I set the mower at its lowest setting. This removes accumulated thatch. I use the clippings as a mulch around perennial flowers and shrubs or add it to the compost pile.

If moss is starting to build up in shady areas, you could apply Moss Out! or a fertilizer containing moss killer in those areas.

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