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March 31, 2012

A rubber tire around the base of a fig tree should pose little concern regarding pollution, but other environmental and soil factors are important in fruit production.

Yard and Garden
March 31, 2012

Q.

I have a fig tree in my garden. When first planted, a car tire was placed around the tree base to hold and direct irrigation water. Recently, we were advised that the tire would/could pollute the dirt around the base as it degrades over time, thus, rendering the fig fruit unsuitable to consume. I have doubts regarding the accuracy of this statement. Tire rubber is extremely slow to degrade, hence if correct; the likelihood of ground pollution from this cause is highly unlikely. What is your opinion/experience?

Initially, this fig gave sweet and plentiful fruit. For the past 5 or so years, it has produced considerable foliage, lots of foliage and new sucker branches, but no fruit. Many sucker branches are growing from the base of the plant; hence, it might be called a bush instead of a tree. Is it time to give up on this tree/bush and start over or can it be saved somehow?

A.

I agree that there is very little potential for pollution from the tire around your fig tree. Tires do decompose very slowly, so any material released will be very slowly released. Some of the chemicals that may be released are large, organic chemicals that cannot pass through the plants membranes into the roots, so they will not be a risk inside the plant. In the soil, they will decompose over time. Many people are now using crumb rubber or shredded rubber from tires as a landscape mulch (after the steel from steel belts is removed) because the rubber crumb is slow to decompose and remains as a long lasting mulch. Another benefit is the fact that rubber “floats” to the surface in soil and will not remain buried, again prolonging the mulching effect of the old tires.

Several factors may contribute to lack of fruit production by your tree. Cold winters that kill the productive branches can result in less production. Some fig varieties produce fruit on new growth produced that season, while other figs produce on “old” wood that developed the previous year. If a fig tree is frozen and branches killed, varieties that produce figs on new wood will produce the first year after the fig tree regrows. Varieties that produce on old wood will not produce figs for at least two years, if they are not frozen every winter. The fig trees recommended for most parts of New Mexico in which fig trees consistently survive the winter are those varieties that produce on new wood. Some covering or deep mulch around the base of the tree during cold winters may help reduce freezing damage.

Over fertilization with nitrogen fertilizer may result in excess growth and little production of figs. Nitrogen stimulates vegetative growth (stems and leaves) at the expense of fruiting. This may be the case for your fig tree. If so, balance the nitrogen with applications of phosphorus fertilizer which supports fruit production. You may need to work to get phosphorus into the soil since phosphorus is not as soluble in water as other nutrients. You may need to punch holes with a spading fork or auger in the soil beyond the drip line of your fig tree and place the phosphorus fertilizer into these holes. If you use an auger to make a ring of holes around the tree, mix the phosphorus fertilizer into compost or potting soil and refill the holes with this compost/phosphorus mixture.

Fig trees are tolerant of arid conditions (grow well in the region around the Mediterranean Sea), but it does need some moisture. Regular irrigation through the growing season and reduced (not totally stopped) during the dormant season will help maintain tree health and its ability to produce fruit.

So called fig trees do indeed grow more as a large shrub. Training to a single or few large trunks increases the risk that a cold winter will kill the tree. Allowing a fig plant to grow with multiple trunks helps it to survive and regrow after extremely cold winters such as we experienced in much of New Mexico in the winter of 2011. A shrub form of fig tree also facilitates harvesting of the figs by keeping the fruit in reach.

For more gardening information, visit the NMSU Extension publications Web site at http://aces.nmsu.edu/pubs/_h, or to read past articles of Yard and Garden go to http://aces.nmsu.edu/pubs/periodicals.html.

Send your gardening questions to:

Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd.
SW, Los Lunas, NM 87031

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist emeritus with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.