Re: Sunflower Problems with Spruce?

Has anyone heard of sunflowers having problems coexisting with spruce trees?
I have a patch that I've planted with sunflowers (Mammoth) for 8 years or so. It is bordered by a row of forsythias and punctuated at the ends/corners by 3 spruce trees (Blue, Norway and [mumble], all former live Christmas trees).
The sunflowers used to do great. Now they get to maybe 15 inches tall and just stall.
I was wondering whether there is a known interaction issue. The trees are getting large (by Christmas tree standards), and this could just be a straight competition problem.
I ask because I need to figure out a new location for next year. One thought is on the other side of the forsythia line, which would not be as directly in competition, but might still be in range of any botanical warfare.
The volunteer sunflowers elsewhere in the yard do reasonably well, at least until the deer find them.
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I see about four possibilites: 1) the spruce are hogging the soil moisture, and/or the sunflowers aren't getting enough applied water. 2) the spruce are shading the sunflowers 3) you've got a pathogen or perhaps something like a nematode, stunting the plants in that area. 4) you've got a nutrient deficiency (sunflowers like fertilizer)
A patch planted elsewhere would probably be a good idea. If you want to explore the other hypotheses, consider digging out a few big pots-worth of soil next spring, a couple from the current spot and a couple from the new spot. Dig in a heavy amount of well cured compost in half the current spot. That will fix most of the soil pathogen/soil pest issues. If compost side does better than untreated side, that's probably the problem. If both stall out again, try watering at an inch a week. If that doesn't do anything after a week, try some general purpose fertilizer.
You can use the potted sunflowers in soil and shade to compare the same soil to each other with shade and sun.
This is hardly a statistically reliable experiment, just something to help get a handle on what might be going on.
It's also possible that you can get somewhat of a crop this summer if you replant now.
Kay
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