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joan_h_gw

Sunburned plants - what to do

Joan.H
9 years ago

Hello! We've had some record breaking heat here in SoCal. Super heat like that is uncommon where I am, and it's taken its toll on some of my plants. In particular, boxwood and Peter Pan agapanthus. They're both pretty badly burned. My questions are these . . . can I just shear the agapanthus way back, like almost to the ground? Will it come back in the spring? The leaves are too small and too many to deal with individually. Sort of the same with the boxwood. Can I give it a heavy pruning? I've never done that before. It gets sheared into a small hedge but never pruned. Got ideas for me? Thanks!

Comments (8)

  • emmarene9
    9 years ago

    I would leave the Boxwood alone and cut back they Agapanthus.
    Think of your Boxwood as being deciduous this year.


    Both plants can tolerate high heat so I don't know what happened to yours. I have both and it gets high nineties and over a hundred here.

  • tapla (mid-Michigan, USDA z5b-6a)
    9 years ago

    Sunburn, technically 'photo oxidation' is different than heat damage. It's unlikely to be sunburn unless your plants were suddenly subjected to more light than they were acclimated to. Example - a heavy pruning that exposes foliage previously shaded by the foliage that was removed, or moving a plant from shade to full sun. The excess light stimulates the release of an O- molecule which oxidizes the first organic molecule it encounters - exactly the same way O- molecules in H2O2 (hydrogen peroxide) bleach (oxidize) organic molecules.

    Heat damage occurs mainly when the plant isn't able to move a large enough volume water that it can cool itself via transpiration. When that occurs there is a cooling process loss and internal temperature increase. Cell membrane leakage occurs, which signals changes in protein synthesis. The plant is severely weakened through rapid use of it's food/energy reserves, and toxins are generated/released because of cell membrane integrity loss and protein breakdown.

    It would be ok to prune any boxwood wood that doesn't have green on it, but leave all branches with green foliage until the plant recovers. If there IS an ongoing drought stress issue, you should work on it to ensure the plant gets enough water. You can cut the agapanthus back to a 'do over' state if you like.

    Al

  • calistoga_al ca 15 usda 9
    9 years ago

    When sunny California is just too sunny all plants should be watered even those not normally requireing water. They will be able to resist sunburning if this is done. At least it will help. Calistoga Al

  • bahia
    9 years ago

    Shearing off sunburnt boxwood foliage in late fall should result in lots of new growth, assuming it gets watered/rains to support fresh growth. Agapanthus can be cut to the ground and will easily releaf.

  • Joan.H
    Original Author
    9 years ago

    With our unprecedented drought, I've been ever so diligent in the watering of my plants, and even some trees. So I don't think lack of water is the problem.

    "Heat damage occurs mainly when the plant isn't able to move a large enough volume water that it can cool itself via transpiration." What would cause this to happen, and how can it be corrected?

  • Joan.H
    Original Author
    9 years ago

    With our unprecedented drought, I've been ever so diligent in the watering of my plants, and even some trees. So I don't think lack of water is the problem.

    "Heat damage occurs mainly when the plant isn't able to move a large enough volume water that it can cool itself via transpiration." What would cause this to happen, and how can it be corrected?

  • tapla (mid-Michigan, USDA z5b-6a)
    9 years ago

    Other factors that can work singularly or in concert to limit a plant's ability to move water efficiently include soil compaction, TOO MUCH WATER (causes a drought response), a high level of dissolved solids (fertilizer, usually) in the soil solution.

    Al

  • Joan.H
    Original Author
    9 years ago

    I'll have to check those things out. Thanks so much!