Sword fern - brownish leaves

Discussion in 'Pacific Northwest Native Plants' started by Margot, Nov 14, 2019.

  1. Margot

    Margot Well-Known Member

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    Again this year, I see some of my sword ferns (Polystichum munitum) are becoming brownish. It doesn't look fungal to me nor are there any signs of spider mites so I'm wondering not only what the cause may be but also whether it might spread to the unaffected sword ferns nearby. All the better if it is preventable or curable. The ferns get regular watering through the dry months and have excellent drainage. They are growing in bright semi-shade.
    Except for being unattractive, the plant seems perfectly healthy.
     

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  2. Sulev

    Sulev Active Member

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    Maybe they got more direct sunlight than expected after the "bright semi-shade" crown cover (oaks?) above dropped its leaves, in combination with too few precipitation?
    According to the Weather in October 2019 in Vancouver, British Columbia, Canada there was ca 20 days long period without any rain in the Vancouver area.
    Maybe your ferns don't just like this kind of exposure to the sun together with cold soil (obtaining water from the cold ground is difficult) and autumn winds? October, 25th was possibly the hardest for ferns, relatively strong winds together with sunshine and relatively cold soil.
    Last picture is of the sporangia, these are no signs of illness.
     
  3. Ron B

    Ron B Paragon of Plants 10 Years

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  4. Margot

    Margot Well-Known Member

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    Sulev - I really appreciate your thoughts but the fact is that many of my sword ferns growing in almost full sun are still perfectly green. I think you're right that it could be a combination of challenges . . . the ferns on the bank where the browning one is located are quite old and I wonder if there are enough nutrients in the rocky soil where they self-seeded (self-spored?). Otherwise, the growing conditions in my garden are very benign; zone 8b-9a.

    Ron - the mystery problem you mention is very worrying and I sure hope a cause is found soon. I'll watch for fronds wilting and/or fiddle heads dying but right now it looks very healthy (except for the browning).

    For now, I'll keep an eye on my fern and try to figure out what else might be at play. At least I can now rule out the likelihood of pests or diseases.
     
    Last edited: Nov 14, 2019
  5. wcutler

    wcutler Esteemed Contributor Forums Moderator VCBF Cherry Scout 10 Years

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    Your question implies that they don't go brown every year. I'm so surprised to read that. I thought they all lost lots of fronds in the winter and got lots of new fronds in the spring. Not so?
     
  6. Margot

    Margot Well-Known Member

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    Polystichum munitum is an evergreen fern. The browning that I see now, especially on the edges of pinnae, is quite different than leaf senescence. Depending on how harsh the winter, sword fern fronds can stay green for a couple of years although they tend to look increasingly tattered as time goes by.

    I try to remove the old fronds just before the new ones are ready to emerge but I'm sure ferns would prefer the old leaves be left as mulch. Fern fronds make a fabulous mulch/compost.
     
  7. Ron B

    Ron B Paragon of Plants 10 Years

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    Partial browning of existing fronds during the winter and spring removal of these by persons concerned about how it looks is typical for cultivated specimens of this plant here in its native area.
     
  8. Sulev

    Sulev Active Member

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    Those of your ferns, who spent whole summer in the sunshine, did not get sudden change in light exposure and moisture conditions in the autumn, after deciduous trees dropped their leaves. Plants often have different leaf structure (number of stomata per area etc) if growing in the shade, compared when growing in the direct sunlight. This can have effect on what is their resistance to drought conditions, even if it is not exactly a meteorological drought but physiological drought.
    physiological drought - Dictionary of botany
     
  9. Ron B

    Ron B Paragon of Plants 10 Years

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    Friend's property on Camano Island - where they seem to share in weather patterns occurring in the Lower Mainland at least part of the time - has other kinds of plants that got discolored by some circumstance this year also. As with your ferns looking as though already affected by significant winter cold, even though it has been for the most part unseasonably mild.
     

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