Pensacola News Journal

For:  Saturday, Nov. 20, 2004

By:   Daniel E. Mullins

        Extension Horticulture Agent

        Santa Rosa County

Allow Plants to Go Dormant Without Unnecessary Help

            Winter is not far away and landscape plants are going through some changes.  When night temperatures fall, day length decreases and soil temperatures cool, top growth begins to slow.  This is a good thing.

            As winter approaches plants begin to store more carbohydrates and the sap becomes increasingly dense.  The more concentrated chemicals within their tissues serve as “anti-freeze,” helping to protect plants during extremely cold weather.  This is known as winter dormancy and is the way of temperate zone, and to some degree, tropical plants.

            It is sometimes better to do nothing than to do something.  Don’t try to help too much this late in the season.  It is too late in the fall to apply fertilizer, even specialty types.  Though fertilizer applications in preparation for winter have received a lot of attention over the past few years, they are not helpful unless the right product is used at the right time.

            The possible need for late season fertilization is based mostly upon turfgrass research.  There is some indication that potassium is commonly low by fall in many of our coastal lawn soils.  To extrapolate and assume that our shrubs and perennials are also suffering from potassium deficiency during the winter is a bit of a stretch.  I have seen no research that indicates that this is a fact.

            Even when the right fertilizer product is applied late in the growing season, it should be done when the plants are still in active growth allowing several weeks for potassium uptake and use before dormancy.  Applying fertilizer to temperate zone ornamentals when the soil is cold and they are already going dormant is a waste of time and money. 

            The “right” fertilizer, for those determined to make a fall application, should be relatively low in nitrogen.  This element, which is listed as the first number on the fertilizer analysis, should be much lower than the percentage of potassium.  Nitrogen stimulates growth which is not desirable when plants are attempting to go dormant.

            Aside from the removal of storm damaged wood, avoid the heavy fall pruning of shrubs. November pruning can stimulate new growth and make them more susceptible to winter injury.  Pruning stimulates growth and essentially wakes up plants when they are trying to rest for a few weeks.

            The judicious use of irrigation water is the most important practice in helping landscape plants to over-winter successfully.  Though not needed as frequently as during the cool season, there are dry periods when a thorough irrigation applied weekly is helpful.  Plants that are growing in moist soil are more cold tolerant than those that are drought stressed.

Question of the Week:  What abut the root system of the big live oaks and pine trees?  Ivan winds rocked the big trees such that the soil at the bases is depressed.  Can fill dirt be applied to stabilize the trees?  Are they more likely to fall during future storms?

Answer:  Enough soil can be applied to return the surface to its original level, but don’t pile up or add soil above the natural grade.  The depressed areas are due to underground air spaces that were created as the roots were heaved during high winds. Some of the added soil will probably disappear over time, as water from rains and irrigation will move it down to fill some of these voids or air spaces.  It can be replaced as needed.

            Though filling the low places can be helpful to some degree, this practice will have little or no immediate effect in preventing trees from falling.  The trees’ ability to tolerate future storms will increase only as time allows the recovery of damaged roots and the replacement of broken ones.