by Fellow rosarians:
OK, this is the first of a series on this that I will post on
fertilizing roses. Since there are/were many posts asking about
rose fertilizer to use, and if MiricleGro works, etc. I will post
this explanation which will be rather detailed. Opinions vary, as
will your rose blooms...
Rose Fertilizers Defined, part I
It seems that the stores have lots of types of fertilizers on the
shelves, and they vary greatly in price. So which one do you buy?
Do you buy the Special Rose formula, or the Super Duper Rose
formula? Should you get the green slow release pellets in the box?
Or the blue soluble stuff in the bags? Should you buy the Miricle
Gro[TM] formula or the off brand next to it for less? Should you go
organic or chemical? Or combine both?
OK, first things first. Every bag or bottle of fertilizer
has to have the % breakdown of nitrogen, phosphate and potassium
on the label, and it is always in that order. Regardless of what
the package says it is for, the formula must be on it. The %
breakdown is labeled in a series of numbers, such as 30-10-10, or
10-15-10. 30-10-10 means that it has 30% NITROGEN, 10% PHOSPHOROUS,
and 10% POTASSIUM by volume. This is a high nitrogen fertilizer,
and is the composition of MirAcid[TM] (a Miricle Gro fertilizer that
is popular). 10-15-10 means that it has 10% nitrogen, 15% potassium,
and 10% phosphate. This is the formula for MiricleGro[TM] fertilizer.
Other trace elements such as manganese, chelated iron, sulfur, etc.
are also listed in fine print. These trace elements are also important,
but not as much as nitrogen, phosphate and potassium.
There are all sorts of %-%-% combinations, and I have seen just
about avery combination imaginable claim that it is specially
formulated for roses. I have also seen the same formulas in bottles at
places like Long's *** with the exact same %-%-% labeled for different
plants and priced accordingly! The "general" house plant food was in a
green bottle for $2.29. The same formula in a yellow bottle was labeled
for "flowering plants" for $2.59. And the violet bottle was labeled
for "African Violets & Orchids" and listed for $2.89!!! And they all had
the exact same %-%-% formula! A similar thing happens with brand
marketing, but I will get into that in a future post. The point is that
the numbers on the packages tell you what the fertilizer is, and not the
brand name or what the lable says it is for.
So you might be wondering what to feed your roses then? It really
depends on soil type (acidic or alkaline) and what climate you live
in. Soil Ph creates a problem chemically in soils and what is true
for acidic soil is quite different in alkaline soil. Here's why:
In acidic soils, phosphorous is not as available to plant roots,
and gets locked up in the soil. something like 1% of the phosphorous
in the soil is available to plant roots. So in acid soil regions, you
need to add more phosphorous than you do in alkaline soil regions.
Here in California, the soil is mostly alkaline, and thus phosphorous
is not needed as much. Likewise, in Oregon where the soil is acidic,
phosphorous is needed more. A similar, but opposite problem exists for
iron. In alkaline soils, iron is not available to plants, and thus the
need to add chelated iron here. In acidic soil iron is available, and
thus not really a problem (nor as much needed in feeding).
As for feeding your roses, in San Diego, CA they will require a lot
more nitrogen and heavy feeding than they will in say, Vancouver, BC,
Canada where they will have a shorter growing/blooming period. roses
tend to be heavy feeders, and as someone said in another post to this
newsgroup, they are more like pigs. They will eat anything. This is
quite true, as UC Davis studies show that fertilizers of all types
and origins will be taken up by the plant and used in the same way.
Regradless of how much you paid for it at the store.
So lets review:
All fertilizers have the 3 main components listed on them in the order
of: nitrogen, phosphorous and potassium in % breakdown. Trace elements
are also listed. The elements needed vary depending on the soil type
and Ph that you grow your roses in. Phosphate is needed more in acidic
soils, and (chelated) iron is needed more in alkaline soils. And finally
roses are gluttons, think of them as ravenous pigs.
More *fertilizer* to come...
Scott
Campbell, CA