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I have two questions regarding the sunflower seedlings in the picture below.

  1. I think my sunflowers are too close together. How much should I thin them and based on their height, does now seem like a good time or should I wait?
  2. Some of them have sort of a burgundy stem (circled in blue) instead of a green one. What does this mean, if anything (They were all planted from the same seeds packet)?

enter image description here

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3 Answers 3

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It will help to find what variety you have, as some varieties need much wider spacing than others.

Here is an idea of what you are looking for via spacing:

  • 2-3' tall matured: Space 10-14" apart
  • 3-4' tall matured: Space 12-18" apart
  • 4-6' tall matured: Space 14-24" apart
  • 6-8' tall matured: Space 16-30" apart
  • 8-12' tall matured: Space 20-36" apart
  • 12'-up: Space at least 30" apart

The wider spacings are better for branching varieties. Sunflowers can be grown tighter, but the result may be unnaturally small heads, on top of very long stems. The wider you space, the shorter the stems you will get, and also larger heads.

You can thin them anytime at this point, but I often wait until the plants are 4-6 inches tall, so that I can be more sure of the vigor levels of the young plants. When you are thinning the seedlings that are very close, place a finger on each side of the seedling you wish to keep, to hold the soil in place while you pull the surrounding plants with your other hand. This may not be necessary, but safe is always better than sorry.

The burgundy color on a sunflower stalk, if it is surrounded by normal green sunflower plants, usually indicates a reddish tinged to full dark purple flower. However, some yellow flowered specimens have a burgundy stalk. If you didn't plant a blend, and are looking for uniform color, you may want to cull these. If this is from a blend, try to leave as many different growth types as you can. This is easier when the plants are a little older.

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Cutting the unwanted plants off at ground level with scissors prevents the possibility of uprooting the ones you want to keep. –  TeresaMcgH Jul 22 at 18:14
    
I'll make sure to keep the dark colored stalks to see what kind of flowers they produce..interesting... –  amol Jul 22 at 19:06
    
@amol Anything new? Are the burgundy plants retaining their color? –  J. Musser Aug 15 at 3:39
1  
@J.Musser - yes, they are retaining their color. I have thinned the plants a little but made sure to keep the burgundy ones. I'll post some pics and also update if/when they flower. –  amol Aug 15 at 21:05

It is suggested that sunflowers be thinned when the first true leaves (the second set, which appears to be about now from your picture) to 1 plant every 2 feet, give or take. 2 feet is the suggested ideal spacing for bigger plants. If you don't care about size or specifically want them smaller you can keep a bit smaller spacing.

As for the purple stems, some sunflower stems have that colour/tint to them, depending on the variety. However, some plants will also show these kinds of symptoms from a Phosphorus deficiency. In extreme cases of Nitrogen deficiency you will see purple leaves/stems as evidence of chlorosis, but I believe that's usually seen is older plants than this. Look at the seed packet to determine if it's a normal colour or not.

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You can do it now. They look tall enough to thin but it won't hurt things to wait a week or so.

It will depend on the variety as to the spacing. As J.Musser stated quite thoroughly, the height at maturity is a factor in the spacing.

I avoid disturbing roots by taking my garden shears and snipping the seedlings off at ground level rather than pulling them. The "thinned" plants will die off and provide the needed space.

I'm guessing you might just have a variety of seeds. It'll be more evident if that's the case once you can see the flower head.

I bought a gallon bag stuffed full of sunflower seeds. They are allegedly all from the same variety of sunflower but there's some variation among the plants - could be genetic variation. Could be that it's really just a variety of seeds. They are similar enough that I think it's the former.

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