High Nitrogen, Quick Release of Fertilizers Keep Plants Green during Cold Weather

Q. Our lawn was beautiful during the summer but started turning brown when it got cold here in Mesquite. This is a fescue lawn and we were told it would stay green all winter long.

A. There are several different kinds of fescue, but the fescue used for lawns is technically called “turfgrass type tall fescue”. Tall fescue lawns stay green through the winter in our Mojave Desert climate if they receive an application of nitrogen fertilizer in late Fall and night temperatures don’t drop below about 15° F.

This is a conventional high nitrogen fertilizer called ammonium sulfate. It is used to feed plants only nitrogen for promoting growth of stems and leaves.Where the nitrogen comes from but conventional fertilizers may contain other ingredients in very small quantities. Some followers of organic principles might call these other ingredients, "contaminants" in the fertilizer. Any fast release slow nitrogen fertilizer will keep plants green longer into late fall and early winter then not applying any nitrogen.

            If the lawn is without nitrogen, and nighttime temperatures drop below freezing, fescue lawns will go dormant and turn brown. Apply a high nitrogen fertilizer or compost to the lawn late in the fall before freezing temperatures.

A high nitrogen fertilizer but derived from dried blood. It is also high in nitrogen and releases it fairly quickly but not as fast as ammonium sulfate. This blood meal is not certified organic by the USDA but many would consider it as "organic" nitrogen.

            You can use any fertilizer if the first number is the highest number on the bag. Examples can be 21-0-0, ammonium sulfate, applied 2–3 weeks before freezing weather hits. In our Las Vegas climate, applications would be around Thanksgiving, or possibly even later if nighttime temperatures don’t drop below freezing.

            Nitrogen, the first number on the fertilizer bag, is responsible for a plant’s dark green color and encouraging new leaf and stem growth. It can also keep plants from going dormant during the winter.

            There is a nefarious side to late applications of nitrogen. Nitrogen applications made in late Summer or early Fall can compromise our winter-tender plants such as many types of citrus. Applications of high nitrogen fertilizer to these plants late in the growing season can cause them to be more susceptible to freezing temperatures. Never apply high nitrogen fertilizers during Fall to plants that might freeze during winter the winter.

The Truth About Deep Root Fertilization of Trees and Shrubs

Q. Is deep root fertilization a good way to fertilize our African sumac tree, purple sage bushes and the purple plum tree?  I’ve seen advertisements from some landscapers for this process.  

Where are the roots of trees and shrubs growing
in a lawn?

A. There is nothing special or magical about deep root fertilization from landscapers or done by yourself. If done properly, and many do not, the fertilizer is injected into the soil at the depth of the roots. This is usually only a few inches beneath the surface of the soil.

            Deep root fertilizer applications have made a name for themselves mostly where trees and large shrubs are growing in a lawn. By applying it beneath the surface of the lawn, high rates of fertilizer are applied without damaging or killing the lawn or causing the lawn to have dark green spots of tall grass where the fertilizer is injected. The rates of fertilizer applied is quite high so the “saltiness” of the fertilizer (all fertilizers are salts of some sort) would normally kill the grass if that fertilizer is applied directly to the lawn.

These are the brown spots in your lawn that will occur
if you drop fertilizer on one spot or place it too shallow
under the lawn. It should be 6 to 8 inches under the surface.

            Also, lawn grasses are fertilizer “hogs”. Because of their fibrous root system they take fertilizer, nitrogen in particular, easily and quickly from the soil thus robbing it from deeper rooted trees and shrubs. By placing a complete fertilizer (one containing all three elements, nitrogen, phosphorus and potassium) several inches beneath the soil surface, it places the slower moving phosphorus and potassium right at where the roots are feeding.

            Commercial companies will usually use a liquid fertilizer and inject it with what is called a “soil needle” or deep root feeder. This is a probe that is connected to a tank on the back of a truck containing a fertilizer solution. A hose comes from the tank through a pump and, under high pressure, the liquid fertilizer is injected into the soil.

Granular fertilizer placed next to a bubbler in wood mulch so
the fertilizer will be moved to the roots by the water
coming from the bubbler.

            Real fancy units will allow the operator to squeeze the handle on the injector (a probe with holes in it to allow the fertilizer solution to injected into the ground) and inject a precise amount of fertilizer solution with each injection. The operator can inject the soil in dozens of places under the tree very quickly an be on his or her way.

            You will know if they are doing it correctly by how deeply they push the injector. If they push it too deeply, the fertilizer will be placed beyond the plant roots and a large amount will be wasted. If they don’t push it deep enough and it is in a lawn, then you may have burn spots in the lawn. Burn spots are usually less of a problem in the winter months.

            You can do deep root fertilize your own trees and shrubs by using tree and shrub fertilizer stakes and pounding them into the soil beneath the soil surface a few inches. You can also do it by irrigating the lawn and, while the soil is still moist, pushing a shovel into the soil in spacings about two feet apart under the canopy.

Fertilizer stake. The plastic cap is placed over the fertilizer
stake so that it does not shatter when pounded into the
wet soil under a tree near the source of water.

            The shovel is pushed into the soil all the way, pushed forward so that the slit cut by the shovel is open, and dropping some fertilizer into the open slit. You then pull the shovel out and push the slit closed with your foot. Irrigate immediately after you are finished.

            If your trees are in a desert landscape with drip irrigation then the whole idea of deep root fertilizer comes into question. When trees and shrubs are watered by drip irrigation then I would question whether deep root fertilizer applications are necessary. All the fertilizer will be “pushed” by watering from the drip emitters.

            Roots of trees and shrubs in a rock or desert landscape will not grow like they would in a lawn. Instead, with drip irrigation, roots grow profusely near the emitters and do not go “searching” for water or grow toward water. They are not psychics.

            With drip emitters is best to drop your fertilizer in slits next to the emitters or use tree fertilizer stakes at the emitters.