Fertilize with care

The first thing many people do when a plant looks stressed or doesn't seem to be growing quickly enough is head for the fertilizer. This might not only harm the plant, but unnecessary fertilizers (and other chemicals) are sure to harm the planet.

Excess chemical fertilizers are washed into our waterways, releasing nutrients that can cause algae blooms that rob the water of dissolved oxygen and can lead to fish kills. Excess chemicals in fertilizer may also find its way into local drinking water supplies.

Whenever possible choose plants that require little or no fertilizer. Native plants are usually a good choice for this. Having your soil tested will also help you determine what nutrients are lacking.

Amend the soil by adding homemade compost and other nutrients. Healthy soil will provide plants enough nutrients without the use of additional fertilizers.

If it is determined that a plant needs fertilizer, choose an organic fertilizer or one that contains nitrogen in a slow-release insoluble form. Nitrogen is one of the chemicals in fertilizer that has the most potential for harming the environment. The other chemical of concern is phosphorus. Always follow manufacturer’s directions when using fertilizer.

If using a purchased fertilizer, choose one that contains at least 30 percent slow-release nitrogen. Also, check the three numbers on the front of the bag to select the right mixture for the type of plant you are fertilizing. The numbers represent the fertilizer's nitrogen (first number), phosphorus (second number) and potassium (third number) contents. Using high nitrogen fertilizer on a plant that does not need it is a waste of money and will eventually be washed away by storm water if not used by the plant.

During the 2009 legislative session, the Maryland General Assembly passed the Chesapeake Bay Phosphorus Reduction Act prohibiting the sale of lawn fertilizer that is not low-phosphorous fertilizer. On or after April 1, 2011, lawn fertilizer sold in Maryland must contain not more than 5 percent of available phosphoric acid. 

Fertilizers with higher concentrations of phosphorus will be allowed only in special situations and for new lawns and turf. Newly planted areas require more phosphorus to promote root growth, while established plants and turf need very little phosphorus. 

The legislation helps protect the Chesapeake Bay from high concentrations of phosphorus that can lead to algae blooms and oxygen depletion. County residents can do their part now by seeking out low phosphorus fertilizers for lawn treatment. It is also a good practice to conduct soil tests before applying fertilizers so that treatments are tailored for local soil conditions. Source

If a plant is looking pale or showing other symptoms of ill health, take a piece of the plant to your local Extension Service office or trusted garden center for help with diagnosis of the problem.

Fertilize during the dry months, when possible, and use the least amount of fertilizer necessary. Do not apply fertilizer within 50 feet of a water body and never fertilize when rain is predicted.

For more information, see: Fertilizing the Vegetable Garden