Ed asked me this question, and with his permission, I'm repeating it, because hearing about fertilizer's behavior in soil might clarify to people how the situation differs in bonsai cultu


-----Original Message-----

Date: Mon Feb 23 16:42:17 EST 2004
From: "Nina Shishkoff"
Subject: Non-bonsai question
To: "Edmund L. Castillo"


My wife has an iris garden, more than 400 plants of identified cultivars, labels with the names of hybridizers and awards won, etc.
Iris people feed in early spring with 5-10-10 or 10-10-20, whichever is available. We are in Loudoun County, 45 miles west of D.C., 15 miles east of the Blue Ridge, sort of fivish on the map. County agent says the statistical last frost is May 15. We h
ad 70 degrees last week but have had snow the last week of April.

I read somewhere, probably on the Bonsai List, that it takes 30 days or so for granulated fertilizer to disolve and enter the roots.

I said:
That depends on whether it's a slow-release fertilizer and what time of year it is. A regular granular fertilizer applied in warm weather should be available almost immediately. In a real soil situation (as opposed to the soil-less situation in bonsai),
fertilizer is picked up by clay particles and organic material and stored, and the rate of release depends on the amount of clay or organic material in a soil. Every time you water the irises, you cause the fertilizer to be released into the soil-water ph
ase, and be available to plants. If your irises are planted in, say, pure sand, they will need frequent fertilizer application. If they are in heavy soil, less frequent fertilizer application is necessary, because the soil is storing more of the previous
application.

Ed continued:
Questions:

1. What is the difference in effect between using 5-10-10 and 10-20-20 on a bed?

No difference, really. 10-20-20 is stronger upon application, but "strength" depends on the volume of the fertilizer and the volume of the soil bed, and the amount of clay in the soil. Again, if the irises are in pure sand [or bonsai mix], it doesn't mat
ter what strength you add; the plants have about 15 minutes to absorb the nutrients or wait until the next application. If they are in clay soil, the clay will pick up the fertilizer and hold it, and the strength at which you added it isn't very important
as long as you added enough to get picked up by the clay. Does that make sense?


2. Given the time it takes for granulated stuff to reach the roots, when should
I fertilize in this very mixed up climate?

You need to fertilize when you are sure of warm weather, otherwise the chemistry of the soil will transform the fertilizer into ammonia, which is poisonous to plants. That's more of a problem in enclosed spaces like cold frames than in open beds, but you
need to know about it. More important in your situation, the irises aren't metabolically active in cold weather, so the fertilizer could get leached out with cold rain before the plants can get to it. So wait until the tree buds are swelling and most dan
ger of frost is over.

Please feel free to answer on the list if you think the question is of general interest, otherwise off list directly to me. Thanks.

I've discussed this before, but some people may not have heard it. The big difference with bonsai is that we use well-draining soil that usually doesn't store fertilizer, so we have to add fertilizer every few weeks. It's a simpler system.

Nina Shishkoff


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