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.

--
Drew Lawson | "Look! A big distracting thing!"
| -- Crow T. Robot.
|

On Tue, 30 Jul 2013 14:35:57 +0000 (UTC), Drew Lawson wrote:
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 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

Not specifically sunflowers, just plants in general. If you go into a spruce wood, you will notice that not much else grows there. Especially not plants hungry for nutrients like sunflowers. I don't think they are like yews, which put out chemicals to discourage plants growing around them. I think they are just very effective at taking up all the nutrients and water for themselves, and being shallow rooted don't leave much left for other things. They also cast heavy shade. Also decomposing spruce needles make the soil very acidic.