Use Compost in Place of Fertilizer

Sudan grass without compost (above) and with compost applied (below) growing in Amargosa Valley, Nevada. Composts can provide alot of benefits to plants including much needed nutrients that improve color and growth.

Q. If I make my own compost, can I use it instead of commercial fertilizers for grass, plants, trees, shrubs?

A. Yes you can. But please be aware that homemade compost is not consistent in fertilizer content and quality. This is because of variability of different ingredients used to make the compost. The ingredients used to make compost directly impact the nutrients found in compost made from it. However, compost is universally good, whether it’s commercial or homemade, when added to soils as a soil amendment.

Spreading compost on vegetable plots between palm trees for soil improvement and fertilizer content.

            When using compost as a substitute for fertilizer, it is important to know its carbon to nitrogen ratio (C:N), in other words how much nitrogen fertilizer it contains. The nitrogen content of a compost is critical. High nitrogen content (low carbon to nitrogen ratio) makes compost “hot” and less of it should be used. If compost has a high carbon to nitrogen ratio (low nitrogen content), then more of it should be applied when substituting it for fertilizer.

When applying compost to lawns a compost drum spreader is used to apply it evenly.

            Commercial composts aim for a carbon to nitrogen ratio close to 20:1 or twenty times more carbon than nitrogen. As this ratio increases to 40:1, the nitrogen fertilizer content decreases. At a ratio more than 40:1, the compost is still valuable but it’s value is greater as a soil amendment rather than fertilizer.

When applied to fruit or landscape trees, compost can be applied in a circle around the trunk so that it doesn't damage the tree. It is then watered in.

            The carbon to nitrogen ratio in homemade compost is managed through what is added to the compost mix before composting. “Woody” additions to compost like wood chips, sawdust and shredded newspaper (sometimes referred to as the “brown” component) increase the carbon to nitrogen ratio.

Compost piles have ingredients that are shredded, water is added to help it all "rot" and  the pile is turned when the temperature inside the pile gets hot, around 160F. Manures are usually used to get the nitrogen content high enough for rotting to begin.

            Additions of grass clippings, leaves of trees and shrubs, and vegetable scraps (referred to as the “green” component) lowers the carbon to nitrogen ratio and make it more valuable as a fertilizer.

            Animal manure (think of it as a concentrated “green” component) is high in nitrogen and added to get the carbon to nitrogen ratio low and improve fertilizer content. If lots of different components are mixed together in the right proportions, green components are balanced with brown components, homemade compost has all the nutrients needed by plants.

            The short answer is “yes”. But substituting a homemade compost for a fertilizer application varies from batch to batch depending on what was used to make the compost.

Not Too Late to Fertilize

Q. My schedule was to fertilize my citrus plants on President’s Day but because of the drop in the temperatures, I decided to postpone. It has stayed cold. So, when should I fertilize?

Keep fertilizer away from tree trunks so it doesn't damage the tree.

A. Everything has slowed down because of the low temperatures. As soon as it warms up would be fine. If they need some extra help, consider foliar feeding them with a tomato-type water soluble fertilizer in three or four weeks. 

Don’t forget to apply iron either in the soil or combined with your foliar feeding. Cold, wet cloudy weather did not let many honeybees out for pollination so these early flowering trees may not have very good fruit set.

Lime Tree Pruning Tips

Q. Please give some tips on pruning my three-year-old sweet lime tree: when to prune, how tall to keep its growth on my limited backyard space, fertilizing, and does the tree have to be pruned annually? 

Readers young lime tree

A. Read most information on pruning of citrus and it will tell you to prune citrus very little. Citrus of any type have few issues that need correction by pruning. They do not need to be pruned to improve fruit production like other fruit trees.

Reasons for pruning citrus

            The primary reasons for pruning citrus are to reduce its size, remove problems like crossing and broken branches, and some thinning to reduce excessive growth.

            They do need to be pruned if you want to keep them smaller. They can be pruned to backspace to about 60% of their mature size. But it should be done every year.

            Prune just after harvesting the fruit so that it doesn’t interfere with next year’s flowering and fruit production. This is also the best time to apply fertilizer. Light pruning with a hand shears and applications of fertilizer can be done anytime of the year.

First, control its height

Identify backspace stems backspace contributing to an undesirable height. These will be vertical or nearly vertical. Follow the stems along their entire length and remove them, entirely, at the point where they become vertical. This may be somewhere deep inside the canopy. It doesn’t matter if that’s the case. Remove them with a clean, close cut.

            The tree wants to become tall. You want the tree to stay smaller. This is where you are at odds with tree. You must control the tree, it should not control what you want.

Get rid of vertical growth

            The best production of fruit comes from stems that are NOT vertical. Consistent fruit production comes from stems that are near horizontal or no more than 45° above horizontal.

Reduce its width if needed

            If the width of the tree is a problem, reduce the length of horizontal or near horizontal stems. To do this, follow the length of the offending stem toward the inside of the tree. Remove the portion of this stem that is offensive at a juncture with another stem. DO NOT LEAVE STUBS.

Remove crossing or broken limbs

            Adding fertilizer to plants, particularly those high in nitrogen (the first number on the bag), should be done every year to maintain a high level of fruit production. But the amount applied should be adjusted according to the needs of the plant. If the tree is growing excessively, reduce the amount of fertilizer applied but don’t eliminate it.

Cool Wet Spring Perfect for Fireblight

Bacterial diseases like fireblight need openings to enter the susceptible plant. Flowers provide temporary openings and let this disease enter inside plants. So do fresh pruning cuts. Fireblight disease spreads from infected to uninfected plants through these openings. Rainy and windy weather helps spread this disease when flowers are open. Honeybees are suspected to spread this disease as well by visiting these flowers.

Cool, rainy weather when pear and apple are in bloom, is perfect weather for fireblight disease. Fireblight is a very aggressive and dangerous plant disease that shows up as new infections in about May in Asian Pear, European pear like Bartlett and some apples. It can be a major problem on Quince as well.

This is why the first evidence of fire blight disease is usually seen by the blackening of the flowers in late spring. From here it can spread into branches and cause severe problems.

            But the disease problem, although unseen, can begin now. The point of entry for this disease into susceptible plants are the open flowers and fresh pruning cuts. Open flowers and fresh pruning cuts provide “fresh wounds” or points for this disease to enter inside the plant. Wind and rain are the usual culprits that spread the disease from plant to plant but even honeybees can be responsible.

Fireblight has spread from a flower or pruning cut and caused more dieback.

            If this disease is seen early enough (usually in late April or May) it can be eliminated easily with a few snips of a sanitized hand pruner, eliminating the infection. But the hand pruner must be disinfected between each cut on the tree or the disease can be spread on the hand pruners through each cut.

Classic textbook dieback and progression of fireblight disease

            There is some disagreement about what to use to disinfect hand pruners but chlorine bleach seems to be the favorite among orchardists. Heat from the open flame a cigarette lighter also seems to work. Some people suggest alcohol and others suggest household cleaners like Pine-Sol.

            Plants that were infected in previous years will show evidence of this disease when new growth occurs in the next couple of weeks. As the name suggests, this damage resembles the black from fire damage. This can be confusing because any damage to pear leaves can turn black. If you are unsure, send me a picture.

            We have had a surge in this bacterial disease over the past few gardening seasons because of our cool wet springs. I will post more pictures of this disease from past years on my Internet blog, Xtremehorticulture of the Desert.

Keep Compost Away from Young Plants

Q. When I apply compost to plants, do I avoid the main trunk area or do I apply up to the trunk?  

A. If soils have no plants in them, I use about 1 inch layer of compost applied to flowerbeds and vegetable beds every year. This compost is turned under or rototilled into the soil before planting. 

Compost can be used as a substitution for fertilizer in vegetable and flower beds even when plants are actively growing in them as long as you can see bare soil. Apply the compost to the soil between the plants or between rows and water it in. 

Compost can be applied to the soil surface and watered into the soil and act like a fertilizer

Compost can be applied to fruit trees in a circle around the trees under the canopy where the soil is wet. The compost should not be piled against the trunks of the trees. 

Compost can be added around fruit trees to the soil surface but keeping in from contact with the tree directly and then watered in. It is very effective when combined with a surface layer of wood chips.

Compost can be applied around desert landscape plants on top of coarse rock mulch. If the rock is coarse enough, it can be washed onto the surface of the soil under the plant canopy through the rocks with a hose. It is best if straight compost does not come in contact directly with soft succulent plants or young trees.

Compost tea brewer, top, and applying compost tea with an injector directly into the soil.

Compost can also be put in with pure water and allowed to "seep" just like tea in a tea bag. The water separated from this combination, compost tea, can be used as a liquid fertilizer and in some cases helps reduce disease problems in the soil or when used as a spray on the foliage.  After the tea has been made the compost can still be used as a soil amendment, but, of course, wit;h a lower nutrient content.

Be careful, though, the type of compost used can make this tea solution very concentrated and can harm plants unless it is diluted with water. It is good to use a salinity meter to judge whether it is safe to apply to foliage directly without dilution or knowing how much to dilute it. The salmity of the compost tea should be below 4 mmhose/cm or dS/m. 

Compost Should Finish Its Cycle before Application

Q. How do I know when compost is safe to apply to plants? Do I measure temperature?

A. Compost is safe to apply when the composting process has completed. Look and smell a compost to see if it is finished. A finished compost will have the same color throughout and the components are not recognizable. Everything looks the same.

Finished compost should have a dark color, the color should be consistent through the compost and the components used tof composting are not distinguishable. 

Commercial compost is safe to apply any time it has finished the composting cycle. Most commercial compost is never sold or marketed before it is finished. The components of a compost will eventually break down and supply nutrients to plants separately but there are some problems doing it this way.

Composting is the same process used by Mother Nature when things “rot”. But in composting, this rotting process is sped up and managed. If you are making your own compost, it is probably a good idea to purchase a compost thermometer.

The type of composting I would use is pile composting. This method mixes all the components together and puts it in a moist pile. The fastest way to get a finished compost using this method is by turning this pile or aerating it when the core of the compost reaches 160° F and wetting it down.

A slower method is the static pile composting method where the pile is never turned. There are much fancier ways of making compost like using forced air or in-vessel composting which can finish compost extremely fast.