Primetime Newspapers
By Calvin Finch, PhD, SAWS Conservation Director, and Horticulturist
Week of January 24, 2005

Blueberries in San Antonio

            Do you like the taste of blueberries?  Do you fondly remember picking blueberries in the North or Southeastern US?  All the blueberry species require acid soil which you would think eliminates them as a plant for San Antonio but three horticulturists from the Texas Cooperative Extension—Jerry Parsons, Larry Stein and Jim Kamas have worked out a way we can grow rabbiteye blueberries in containers here in San Antonio.  Here are their instructions:

            Blueberries require a pH of 4.0 to 5.0 good plant growth.  The plants' feeder roots are very close to the surface and they do not have root hairs; therefore, good soil moisture management and mulches will also be required.  

            The plants should be planted in a whiskey barrel size (20-30 gallon) container.  A soilless peat-base mix that drains rapidly should be used.  Ideally, when you pour water around the base of a plant, water should soon be coming out of the bottom of the container.  This not only indicates proper drainage but also enables leaching of fertilizer salts, which, if accumulated, can damage a blueberry plant's roots.  Blueberries thrive in 100 percent peat moss, so there is no limit to the amount you can use and if you are doubtful about the pH of the potting mix you plan to use, simply add more peat moss.  Be sure to incorporate a slow release fertilizer such as Osmocote into the peat-base potting mix.  Avoid the use of rapid-release, nitrate fertilizer and use an acid-based, water-soluble fertilizer once a month during the growing season after the plants are established.

            Once you have mixed or purchased a well-drained soilless peat-base mix in which to grow the blueberry plant, be sure that the container being used has adequate drainage capabilities.  Drainage holes may have to be drilled.  When considering drainage holes, the old saying, "The more, the merrier" definitely applies.  Also, don't worry about lining the bottom of the container with course gravel or charcoal to expedite drainage.  Recent research indicates that such a gradient in materials actually impedes drainage.  Heavy duty coasters can be attached to the bottom of the containers before potting mix is added to allow ease of movement even though blueberries will not have to be protected from cold weather--they require cold weather in order to fruit.

            Another critical key to successful blueberry production is sunlight.  All berries require full sunlight all day for maximum production.  Minimum is eight to ten hours of direct (not filtered) sunlight a day.  Not only do the plants require full sunlight when they are planted, but also as they continue to grow.  Over time if they become shaded by trees in your landscape, their production will be much less.

            Some blueberry varieties require cross-pollination so variety selection will be critical.  However, Tifblue has been shown to be self-fruitful and is the most universally outstanding rabbiteye blueberry grown to date.  The fruits are large and light blue.  The bush is vigorous and very productive.  Tifblue is more cold hardy than most rabbiteye blueberries varieties and receives adequate chilling (cold temperatures) to fruit as far south as Pleasanton, Texas.  Tifblue rabbiteye blueberries require little pruning.  Lower limbs can be thinned out to keep the fruit from touching the soil, and excessively vigorous upright shoots can be thinned out several feet from the ground to keep the center of the bush open and to keep the bearing surface within reach.  Spindly, weak, or dead branches should be thinned out annually during the dormant season. 

            Blueberries have a very fine and fibrous root system so mulching is a must.  Use some sort of organic mulch such as sphagnum peat moss.  Avoid manures since most are alkaline and salty.  Because culturing plants in containers severely limits their root spread, frequent watering and fertilization are essential.  As plants grow larger, more watering is required because water is being absorbed and transpired.  As temperatures increase more water is evaporated from the mix and transpired from the plant.  Check the moisture level of the mix with your finger before watering.  If you feel moisture with your finger DO NOT WATER.  Blueberries require good-quality water.  It would be best if you could use rainwater or air-conditioner condensate for irrigation.  To acidify SAWS water add 1 tablespoon of vinegar to a gallon of water.

            The fruit of the Tifblue variety will ripen over a 4 to 6 week period.   A normal season can extend from late May to late July.  Don't pick the berries until they are fully ripe; otherwise the fruit will be bitter.  Once the berries begin to ripen they should be picked every 3 to 5 days.  Birds love blueberries as much as gardeners but the bush is easy to cover with bird netting.  A mature bush can produce 15 lbs of berries.  If rabbiteye blueberries in a container sounds like something you would want to try, visit your favorite nursery, many are featuring Tifblue blueberries at the present time.