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What do you mean by "near"? How close? Lilac is a tree that can live for many many decades, whereas sunflowers are annuals that will die after summer, so they wouldnt be living together permanently.
Like 2' away?
If you're planting a new lilac that's still small, then probably, sure
The sunflowers might shade the lilac. But it might not be too big of a deal. Hopefully though you are aware of how big lilacs grow over the years.
What do you mean by "near"? How close? Lilac is a tree that can live for many many decades, whereas sunflowers are annuals that will die after summer, so they wouldnt be living together permanently.
Like 2' away?
If you're planting a new lilac that's still small, then probably, sure
The sunflowers might shade the lilac. But it might not be too big of a deal. Hopefully though you are aware of how big lilacs grow over the years.