Thanks to Mary Sue for introducing the timely topic.
I used to use bone meal in my bulb potting compost, but I stopped because
it attracted too many animals, including my dogs. I don't think it did any
harm, though. I have never applied superphosphates, but I know at least one
good bulb grower who does. Some years I have mixed a commercial "bulb food"
into the potting soil -- a cheap generic brand, I think.
Primarily, I rely on liquid fertilizers. Last year I acquired a fertilizing
system (EZ-Gro) that hooks into the hose and mixes the fertilizer at what
is said to be a steady dilution, though (as John Lonsdale mentioned to me;
he has one too) I can't see how it could stay steady over a long period of
watering. Anyway, it hasn't killed any plants, so it is not too strong. The
dilution is adjustable. It makes this task far easier than it was before,
when I was mixing the solution in a garbage can (Brit. dustbin) and
applying it with a hand watering can!
I use one of the several "root and blossom" formulas available commercially
("tomato food" is good too); these have a lower proportion of nitrogen than
general-purpose soluble fertilizers. I apply one feeding in fall and three
in late winter through mid-spring. Since I repot all the bulbs every other
year, they also get fresh minerals and some organic matter at that time. I
do not use manure of any kind in the potting soil, because I think it may
promote rotting, but I think it's all right to use well-aged manure on
certain bulbs, such as lilies. Alstroemerias like manure, as well.
I also fertilize new seedling bulbs, but with a weaker solution (about 1/4
the rate recommended on the container).
I think it's a bad idea to apply foliar feeding to many bulbs, because
splashes of fertilizer seem to promote Botrytis or other infections on the
leaves; probably nurseries apply so much fungicide that this is averted,
but I don't use fungicide except in emergencies. When I apply the
fertilizer with the hose, I use a water wand with a small rose that keeps
the liquid down on the soil.
It's important to feed bulbs well if they are being grown in containers, as
many of mine are. Out in the open ground, they have more resources. Now
that I'm switching gradually to mesh pots instead of clay, I find that
certain plants with wide-ranging roots grow and flower much better, and I
suppose this is due in part to getting more nutrients as they extend their
roots out through the mesh.
Mary Sue didn't mention lime, but pH is important in facilitating the
plant's use of certain nutrients. I rarely add lime to my bulb soil, but
perhaps I should. When I do add lime (mostly for alpines), I use a product
called Cal-Pril, which is slow-release and granular, and can be applied in
the garden with a lawn fertilizer spreader.
For garden fertilizer, including areas with a lot of bulbs, I apply a
granular fertilizer made for use on nursery perennials and shrubs. It
contains both major nutrients and trace elements. It releases over 6
months, but it is not an Osmocote-type product. I haven't seen this type of
fertilizer at garden centers, but the farm stores around here sell such
products. I apply it in April or May. Parts of the garden also get
topdressings of compost or manure when I have the time and energy.
Jane McGary
Northwestern Oregon, USA