Expert: Long Island Gardener - 4/23/2007

Question
What type of begonia likes full sun? What fertilzer do yall recommend for this begonia? 8b.

Answer
Begonias as a group are not full sun plants.  They'll survive, but they'll be stressed.

The common Wax Begonia ('Begonia semperflorens' to botanists) is the one that performs better than other Begonias under the most intense rays.  Wax Begonias with bronze leaves grow even better.

The American Begonia Society (http://www.begonias.org/begonian/begonianItem.asp?ArticleID=32) endorses full sun exposure for most B. semperflorens: 'Many new varieties grown for bedding use are F1 hybrids and come in different colors... They have no special soil requirements and will grow in full sun except in hot, dry climates.'  Note however that 'filtered shade' is quite acceptable to these plants -- one reason for their massive popularity.

Rhizomatous Begonias, known best for their creeping habit and intricately patterned leaves, have their own page on the American Begonia Society website (http://www.begonias.org/greenhouse/byType.asp?CAT=rhizomatous) are not full sun plants.  The beautiful Tuberous Begonias, which have stunning flowers and go dormant during winter, will shrivel in full sun.  Where many houseplants DEMAND full sun, most Begonias are usually reserved for situations that cannot provide a whole lot of sunshine -- they do very, very well in shade.  Full sun will kill many Rex or Tuberous Begonias in a few hours.  B. semperflorens is the exception, not the rule.

As far as your question about fertilizer, the ABS and I agree that you don't need to do that much for this plant.  But the ABS backs the synthetic fertilizer system: 'A fertilizer program should depend on a complete fertilizer (such as 20-30-20) applied every two to three weeks, with a high-phosphorus (0-10-10) formula substituted every third or fourth feeding.'

I maintain that the high concentration of chemicals required to produce a fertilizer with a 20-30-20 punch is good for no plant.  I still believe the more mellow 7-3-2 organic formulation of, for example, Cottonseed Meal is far superior way to grow these plants.

Cottonseed Meal is a by-product of cotton manufacturing.  It has a slightly acidic effect on the pH, making it an excellent amendment for potted Gardenias, but a small amount is also beneficial for plants like Begonias.  The nutrients are easy for plants to access in warm soils without the threat of burning of roots.

The Virginia Cooperative Extension backs Organic fertilizers in one recent posting (http://www.ext.vt.edu/departments/envirohort/factsheets2/fertilizer/jan89pr6.htm...) that I quote here for you because potted plants usually get the full chemical treatment and therefore none of the benfits of Organic fertilization.  But, they point out, 'Compared to Synthetic fertilizer formulations, Organic fertilizers contain relatively low concentrations of actual nutrients."  Instead, they note, it is best to 'increase the organic content and consequently the water-holding capacity of the soil.'  Organic fertilizers 'improve the physical structure of the soil which allows more air to get to plant roots.'

Organic fertilizers support bacterial and fungal metabolism.  Mycorrhizal Fungi, which make other nutrients more available to plants, THRIVE in soil with lots of organic content.  Synthetic fertilizers do NOTHING for soil structure, and they damage living microorganism populations.  Mycorrhiza in particular 'extract mineral elements and water from soil for their host plant' (http://www.planthealthcare.com/fungi.html).

Simple questions, perhaps a little over complicated by me -- let me know if you need clarification.  Meantime, thanks for writing.