Feeding Bulbs. Was Re: [pbs] Slow release fertilizers
J.E. Shields (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

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Jim Shields USDA Zone 5 Shields Gardens, Ltd.
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Tel. ++1-317-867-3344 or toll-free 1-866-449-3344 in USA