Fertilizer Injectors Are Timesavers but Can Cause Problems

Q. We have a fertilizer tank attached to our watering system.  I've had it checked and it is working, as in past years.  However, this summer most of the plants in my perennial flower garden, yellow bells, and bougainvillea are green but few blooms.  Lantanas and purple rubella are blooming well.

A. Fertilizer tanks attached to an irrigation system can be a big plus for the overall landscape quality. However there are some things you should realize about using fertilizer tanks and fertilizer injectors. 

First of all plants receiving the most water, also received the most fertilizer. When we use fertilizer injectors it is best to have them inject fertilizer several minutes after the cycle begins and shut down several minutes before the cycle turns off. This gives a better fertilizer distribution to all of the plants on that circuit and cleans the irrigation lines out of any extra fertilizer. 

Water containing fertilizer sitting in irrigation lines will frequently contribute to plugging because of algae and bacterial growth that occurs in lines that contain water laden with fertilizer. If you don't have this luxury of flushing the lines with clean water, you can flush the lines yourself once a month with freshwater by turning off the injector for a few irrigations. You might want to consider not having the fertilizer tank on all of the time but using it periodically, perhaps once or twice a month, instead.

Air release valve for drip irrigation using a ball to close the valve

Air release valve for drip irrigation using a diaphragm to close the valve

Typically, plants at the beginning of an irrigation line receive more than those at the end of an irrigation line. You can eliminate some of this problem by installing an air release valve somewhere along the irrigation line. This allows trapped air to exit the irrigation line and speeds the delivery of water and fertilizer along the line to all of the plants. Otherwise air can be pushed ahead of the water and slow the delivery of water and fertilizer along the length of the irrigation line.

The type of fertilizer you are using may impact the plants as well. Try to use general purpose fertilizers with the ratio of 3-1-2 or 4-1-2 (nitrogen-phosphorus-potassium). We usually want to apply very low levels of phosphorus if we are feeding plants continually. Phosphorus can build up in the soil and become a problem if too much is applied. If particular plants require higher amounts of phosphorus than these plants can be sprayed on their foliage with a high phosphorus fertilizer or the fertilizer can be applied at their base and watered in.

From the sound of your email, you may be applying too much nitrogen. I would tend to use your injector once or twice a month if it is on continuously now. Let me know how this works for you.