Feeding Bulbs. Was Re: [pbs] Slow release fertilizers

J.E. Shields jshields104@insightbb.com
Thu, 19 Feb 2004 05:40:28 PST
Hi Kathy and all,

Bulb food is a fascinating topic, but let me second the comments of Alberto.

The only careful studies I have ever heard of are those discussed in such 
books as "The Growth of Bulbs" by A.R. Rees (Academic Press, London and New 
York, 1972) and "The Physiology of Flower Bulbs" by A. de Hartogh and M. Le 
Nard (Elsevier, Amsterdam, 1993).  Those findings dealt mainly with 
Narcissus, Tulip, and a few other varieties of bulbs that are produced 
commercially in huge quantities.  We have to extrapolate from those to 
other bulbs.

Essentially, all bulbs need to be fed only once or twice a year:  when the 
roots are active and when the tops are actively growing.  In all cases the 
bulbs need relatively large amounts of nitrogen (N) and potassium (K) and 
relatively little phosphorus (P).  In the fertilizer analysis numbers, they 
are  in the order N - P - K and expressed (in the USA anyway) as 
percentages by weight of N as simply nitrogen, of P as phosphorus 
pentoxide, and of K as potassium oxide.  A fertilizer listed as 14 - 14 - 
14 would contain by weight 14% N, 14% P2O5, and 14% K2O.

In clay-containing soils, excessive phosphate builds up and can then bind 
iron, causing iron-deficiency chlorosis.  In clay-free potting mixes, the 
excess phosphate simply washes out, and then causes no harm.

Most exotic bulbs (i.e., from someplace other than where you are growing 
them) are at least a little stressed all the time, so they are much more 
sensitive to pathogens like fungi and bacteria than they might be in their 
native habitat.  Excessive fertilizer salt build-up can stress the 
roots.  Organic fertilizers can feed and encourage the fungi and bacteria.

It sounds from the above as if it is impossible to grow exotic bulbs.  In 
fact, as Alberto pointed out, bulbs evolved to help plants survive times of 
environmental stress.  Any one of us may not be able to grow them all, but 
most of us can grow most of them.  As we learn to grow the more sensitive 
and demanding bulbs, we learn more about growing bulbs.  This and similar 
plant lists are excellent schools where we can all learn more.

Good growing!

Jim Shields
in central Indiana (USA) where the snow is melting at last

Jim Shields             USDA Zone 5             Shields Gardens, Ltd.
P.O. Box 92              WWW:    http://www.shieldsgardens.com/
Westfield, Indiana 46074, USA
Tel. ++1-317-867-3344     or      toll-free 1-866-449-3344 in USA

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