Water & fertilize bulbs in spring or fall?

[Pelvis Popcan]

I'd like to get some input on the group here on when it's best to water and fertilize established bulbs (bulbs that have grown and bloomed for at least one year). I understand it makes sense to add a little fertilizer and water to a new bulb planting.

My particular bulbs are daffodils and bearded iris. Technically bearded iris isn't a bulb, but I suppose this could apply to any perennial.

I've read arguments that go both ways.

One says don't water or fertilize in the fall because plants go dormant then, and the added fertilizer might encourage the plant to stay active, and the added moisture might cause the dormant bulb to rot. So it should be done in the spring as soon as new growth starts.

I've heard arguments that say that once a bulb starts growing in the spring, it will not absorb any water or fertilizer applied to it at that point and for the rest of the season, so it should be done in the fall.

I've read that most bulbs (tulips, daffodils, etc.) are members of the lily family and originate in mountainous areas of the mediterranean. There they are only active in the wet spring, then go dormant for dry summers and freezing winters. The Dutch/German hybrids that are available today have inherited this behavior.

So it seems to me that if the bulb is dormant in the fall, it wouldn't make sense to fertilize until very early spring, say April 1.

What do you think?

[Frogleg]

I fertilize daffodils in the spring when they are growing. A search on

iris fertilize

and a brief look at some references says that's the time to fertilize iris, too.

[SugarChile]

I'll state up front that this is hearsay, so don't jump on me because I don't have documentation.

A friend went to a lecture by at Brent and Becky's Bulbs, a well respected bulb nursery and vendor. The owner said she had discovered through her own trials that it was beneficial to fertilize established clumps of daffodils in the fall, when root growth was taking place. She said she was able to delay or avoid dividing the clumps with fall fertilization, and she got abundant bloom.

I have a lot of daffodils that have been in place for almost 20 years, and for a variety of reasons I am loathe to dig and divide them. I tried fall fertilization, and have noticed a definite increase in bloom count.

For what it's worth, Sue [e-mail] Zone 6, Southcentral PA

[Pelvis Popcan]

Thanks for the input! So the bulb is NOT dormant in the fall then, as root growth is taking place.

It probably wouldn't hurt to do the Iris then as well I'm betting.

"SugarChile" wrote:

[SugarChile]

That's correct. The root growth actually starts in late summer, as I've found to my bemusement when I've been late to dig and divide. This is also why new bulbs are planted in the fall, so they have time to develope roots before winter sets in.

Well, I wouldn't be too quick to take that leap of faith.....These are two very different types of plants we're talking about. The daffodils are true bulbs, and the iris are rhizomes. The daffodils don't have foliage in the fall, so there's no danger of pushing them into green growth that won't harden off properly. The iris do have top growth, and need to go dormant, so I think that would contraindicate fertilization. As I understand it, irises shouldn't be heavily fertilized at all--it can make them more susceptible to borers and rot--but I'm not the iris expert, perhaps someone else will chime in here.

Cheers, Sue