Growing Tender Bulbs in Cold Climates--Tow

Ken K
Sat, 12 Apr 2003 16:21:02 PDT

There are a lot of theories on the subject of fertilization, here are
a few of my favorites:

Rodger Whitlock wrote:
> Myself, for potted bulbs I most often use "soluble tomato food" with
> an analysis of 7-28-28. The recommended rate for this fertilizer is
> 5 grams per liter of water (1/2 teaspoon per quart).
> However, I apply it to potted bulbs at about 1/4 this strength. I
> figure that the rate for a potted plant should be considerably lower
> than for a plant in the open ground to avoid fertilizer burn.

Depending on the cultural habits of the grower, plants in a pot might
technically require more fertilizer, since they require more frequent
waterings, and the soil is 'rinsed' of nutrients more often. Also,
plants trapped in a container don't have the expansive, unrestricted
root system that a plant in the ground enjoys, and are perhaps more
'needy' because of that. I also use ¼ strength dilutions on my
'exotic' bulbs, but I'm usually fertilizing weekly during growth,
which is every hand watering in some instances.

Fertilizer burn is a frequently misunderstood topic, and the subject
of much gardening folklore. For those readers who aren't familiar with
the phenomenon, fertilizer 'burn' is simply a condition where the
planting medium has become more saline than the root tissue of the
plant. This reverses the passage of water between the soil and the
root tissue, desiccating the plant. Fortunately, this is generally
difficult to achieve when using water soluble fertilizers. In the
past, I have used 'significant' overconcentrations (5 Tbsp./Gallon--5x
the recommended application) of Rapid-Gro (23-19-17) on potted plants
growing in full sun and have seen no evidence of 'fertilizer burn'.
This should assuage the fears of those who are afraid to fertilize

Fertilization needs to be balanced with overall culture, with the end
goal of steady, healthy growth and good performance. If the climate is
rainy, then fertilization may be decreased a bit. This seems at first
to be a contradiction with my previous statement, but rainfall seems
to give plants a growth boost of its own. Plants in full sun and lean
medium should be fertilized a bit more.
> Sometimes I use Phostrogen (10-10-27) at a rate of 1 g of powder per
> liter of water (about 1 teaspoon to an ordinary 2-gallon/10-liter
> bucket). Some bulb growers here have great success adding just a
> pinch of Phostrogen to the watering can each time they fill it.

I like the balance of that. I don't mind a higher nitrogen number--I
figure that I can always dilute the fertilizer accordingly. What I
don't like is a high proportion of phosphorus in relation to the other
macronutrients, since P can build up in soils and become toxic. I
understand that the type of nitrogen in the fertilizer may be more
important than the amount, particularly when it comes to bulbs. I
believe I heard that nitrite N is preferable to nitrate N, but I might
have this wrong. Am I thinking of calcium nitrite perhaps? This is
supposed to be less rot-inducing, but difficult to find in
commercially available mixes.

Trace elements are essential for container growth - especially with
plants that are being grown in lean mixes. It can reduce the need for
regular repotting. I think that my favorite bulbs - South African
amaryllids - are at their best when repotting infrequently. Every time
they are repotted, there is unavoidable root damage, and another
opportunity for rot to take hold.

I've been using liquid Ironite lately, because it has micronutrients
and good 'numbers' as well. (approx. 4-6-1) 

Ken Kehl
East S.F. Bay Area, Ca.
USDA Zone 9 (mediterranean)
-2°C to 38°C

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