Experiments in rooting grapefruit cuttings
I've previously tried rooting grapefruit cuttings in water in a windowsill (probably about four times). Each time it failed. The cutting would eventually dry up and die, with no roots, after some weeks. I didn't use hormone-rooting powder, however (but that would dissolve in the water, rather than stay on the stem, unless I tried rooting it in soil).
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I figure part of the problem is algae. Light from the window causes algae in the water to grow, and that algae may be competing with the grapefruit tree cutting.
So, my grapefruit tree was getting too tall for my room; so, I pruned off a couple pieces, which I'm trying to root as cuttings in water, again--except this time, I'm trying it in the closest where it's dark (instead of the windowsill). The rationale here is that algae won't grow in the dark, clouding the water, and coating the stem. Also, the sun probably won't dry up the leaves eventually (if they die, they might die a different way). So, maybe it'll grow roots, this time; yeah, it doesn't have light to feed the cuttings, but the cuttings probably have starches and stuff stored up in them (they are tree cuttings, after all), which they could use to grow roots.