fertilizing bulbs

Alberto Castillo ezeizabotgard@hotmail.com
Tue, 12 Apr 2005 17:29:46 PDT
Dear all:
           What an interesting thread. After all, improper fertilization is 
the second cause of bulb loss, after improper drainage. Truly regret not to 
have the time to mingle more often. Some comments

Yes, the reason for proper cultivation of Dutch bulbs is the North Sea 
climate. It provides perfect conditions for ....those that can be grown in 
the North Sea climate. There are not many places where fields of tulips, 
hyacinths, Fritillaria imperialis, etc., could be seen like there. No amount 
of fertilizer would produce such crops if the range of temperatures were not 
adequate for growth.

Yes, the Dutch bulb farm fields are former sand dunes added with peat in 
enormous amounts to provide some nutrient retention. They are leached very 
rapidly hence the apparently enormous quantities of fertilizer..Actually, 
this case is studied in plant nutrition as one in which quantities (kindly 
quoted by Jim) can be very misleading. If applied to normal soils they would 
burn roots and grow soft, juicy plants that would attract pests like 
beacons. In the Dutch bulb fields they are just enough.

Yes, an "organic"" soil would contain very few pests that would devour each 
other to reach a peaceful balance. Unfortunately, this can be achieved in a 
small garden or plot by adding really substantial quantities of organic 
matter which in the Dutch bulb fields is unthinkable. The problem they have 
and that force them to sterilize the soil  is nematodes that spread viruses 
while feeding and living on the bulbous plants roots. In the past strong 
chemicals  were used to control the nematode population but now these are 
forbidden (the chemicals, not the nematodes!). Among them methyl bromide was 
easygoing but later found to have terrible  effects on the ozone layer and 
banned. Dutch bulb producers are desperate with these problems and have come 
to find more environmentally friendly procedures (like flooding the bulb 
fields in summer when the bulbs have been lifted to interrupt the nematode 
life cycle). They know well how dangerous viruses are to their crops and in 
fact lots of Narcissus, Scilla, Brodiaea 'Konigin Fabiola', reticulata and 
Dutch irises, alliums, muscaris and a number of others can not be cleaned of 
their virus infection in any affordable way. A lot of research is being 
carried on along this but results are less than mild. The general consensus 
among them is not to worry so long as viruses do not affect the sales.

Yes, the information provided first and that kicked the ball rolling 
concerning bulbs (winter growing ones, of course) being able to use 
nutrients in the Fall period between root emision and leaf emergence and 
that raised so many eyebrows originally came from the Dutch Bub Growers 
Association research laboratories, not a cookbook recipe as someone 
mentioned. Admittedly it sounded odd the first time I learn about it since 
it seems so obvious that "no leaf, no feed" but a number of experiments 
proved it right. Rodger's experience along with Mr. Zonneveld mention of a 
Fall fertilizer application point to it. Actually, it makes a lot of sense 
because many of these cold climate bulbs use the Fall rains to produce roots 
that remain alive and waiting for the snow melting (in the wild) to produce 
foliage and flowers all within a rather short time. It is logic that these 
roots would take any advantage to capture whatever nutrient is available 
even if "no leaf".

As for info on potassium affecting the availability of magnesium, 
comparatively few bulbs will suffer from magnesium shortage, mainly those 
growing on dolomite: some bearded irises, Junos, Reticulatas, some tulips, 
Ungernias, etc. All  the others are positively affected by potassium supply, 
including those from the four corners of the world and those that are 
poisoned by phosphorous like South Africans and Australians.

As for the fact mentioned that bulb plants would not be able to absorb 
nutrients between the flower production and the beginning of dormancy, only 
few of them had their leaves gone by flowering time: Leucocorynes, 
Conantheras, Zephyra, Calochortus, Brodiaea, Pabellonia, etc. The rest have 
leaves then and are very active manufacturing food to fatten the bulb.

On our behalf concerning our frequent errors in fertilizing our bulbs it 
must be pointed out that bulbs are pretty indifferent and do not apparently 
react properly to nutrients provided! I suggest you the use of indicator 
plants. These must no be monocots but rather frugal, not fussy and quite 
easy to grow dicots. My favorite for this climate is Lamium maculatum, you 
see, no exotic gem. Apply a weak solution (as weak as you want, even VERY 
weak) of a foliar formula fertilizer to your bulb plants and then to the 
indicator plant. You will not believe your eyes as the dicot will respond 
immediately to the extra nutrition by making new growth, even changing the 
appearance of the adult leaves. This change will last for a long period even 
one or two months. This will give you a proper idea of how much is too much. 
By diminishing the amount of fertilizer in the solution you will notice that 
effects are obtained even with doses that are very minute. Of course you can 
do it with any type of fertilizer but a foliar formula will give cleaner 
resutls as there will be no danger of the soil meddling and blocking some 

Bob's naive question is not naive, he knows what he means. He is an 
experienced grower and a friend of the late Stan Farwig who had a fabulous 
collection in the Bay Area. Stan had made a number of experiments concerning 
complete formula fertilizers and found that they adversely affected his 
plants and stopped using them altogether. Yes, yes, improper fertilizing 
shortens a bulb life. Strangely (or not) there are very few bulbs native the 
very nutrient rich pampas of Argentina and Uruguay. And countless ones in 
the miserably poor soils of South Africa.

African Violet fertilizers have high potassium formulae. Are they available 
in your area?

All the best

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