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Plant Answer Line Question

Keywords: Grevillea, Nandina domestica

I had a Nandina that I decided to remove today after this winter's freeze. While digging it up I noticed that the root tissue was bright yellow. The roots seemed fine otherwise--no odd smell, not mushy. Is this color normal for Nandina, or is this a sign of a virus? I lost another Nandina to a mysterious disease that looked like a mosaic virus, but that plant was nowhere near the one I just removed. I planted a Grevillea victoriae in that spot, assuming that diseases affecting Nandina would not affect it. Is this correct?


The yellow roots of your Nandina are normal. Nandina is in the family Berberidaceae, along with Mahonia and Berberis, which also have yellow, fleshy roots. Here is more information about Nandinas:
Clemson University page on Nandina

Nandina sometimes suffers from powdery mildew, which is usually not serious, and there is information about this plant occasionally suffering from a mosaic virus and from anthracnose. Here is information about the diseases occasionally affecting Nandina.
Image of Nandina leaf spotting from University of California, Davis Integrated Pest Management

Grevillea is in the Proteaceae family, and I have not found any information that suggests it would be either vulnerable or immune to the diseases which affect Nandina. Some plant diseases affect multiple plant families and others are more narrowly focused. In their native Australia, Grevilleas are not known to suffer from diseases. In our climate, I imagine that cultural and weather conditions would be of greater concern than diseases.
Gardening Australia factsheet
Oregon State University Landscape Plants database information about Grevillea victoriae, excerpted here:
"Sun to partial shade (best). Well-drained, sites, may need occasional summer water to prevent bud drop. Fertilize lightly, avoid fertilizers with a high content of phosphorus."

Date 2018-03-01
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Plant Answer Line Question

Keywords: Cold protection of plants, Grevillea, Potting soils

I have a Grevillea victoriae that I bought 2 years ago. It's about 2 ft tall and is in a pot with bagged soil and sand added for better drainage. It hasn't bloomed much, but it was trying. This year it has a lot of frost damage, and I'm not even sure it's alive.

When can I expect to see new growth? Should I prune off the damaged areas and cross my fingers?


The usual rule of thumb about winter-damaged plants is to scratch the surface of a branch or stem with your fingernail to see if there is green underneath. If there is, that is a good sign. Then, you should give the plant until late June or early July to show signs of resurgence from the damage. I will include below an entire newsletter item on this topic from Plant Amnesty's Cass Turnbull:

January 2009 e-mail newsletter: Is Your Frozen Shrub Dead? by Cass Turnbull
"After an extraordinarily cold winter in Western Washington, many garden owners will want to know what to do about the damage to many of our not-completely-hardy shrubs. With many of our broadleaf evergreens, it's common for their leaves to turn brown or black and eventually fall off. The plants themselves are probably still alive. To check, use a hand-pruner blade to peel back a little bit of the "skin" to see if the cambium layer just beneath is alive (green) and not dead (brown). If alive, it'll probably flush out with a new set of leaves. So don't panic if you shrub looks dead. Wait and see. How long? By June you will have an answer.

"By then, those that can put on a new set of leaves will have done so. If you can't stand the sight of the stricken brown shrub until June, try running your hands along the branches to knock the brown leaves off. Then, the plant might seem to be deciduous, not dead. By the end of August, the final report will be in. Freezing weather sometimes does internal damage that doesn't show up until after the stress of the summer "drought". A shrub may look okay through June and July, but then, while it is pumping H2O like crazy trying to keep up with the heat demand in August, some portions can collapse, and you will see die-back. (The non-scientific explanation is my own and may be a little, well, anthropomorphic.)

"Many evergreen shrubs, such as escallonia, that suffer freeze damage, will die from the tip back. These shrubs respond well to radical size reduction which in this case means big ugly cuts to the point of green wood. The plants will "break bud" just below your cuts and many new green-leafed shoots will rather quickly grow out to hide the cuts and provide you with a "new" plant by the end of the growing season.

"Often, (for example,in the case of choisya), branches will split, break or splay flat to the ground due to snow loading. Get your loppers out and whack everything back to 4" to 6" off the ground. Yes, it's really Okay. I promise. I have done this thing many times. As soon as the growing season begins, the majority of cut plants will spring into action. As the renovated shrubs grow up, it is advisable to pinch them back every so often, to encourage branching and thicken them up. 'Pinching' means a very light heading, just nipping the end bud of each branch with your fingernails or hand-pruners."

You may find this link to a Northwest grower of Grevilleas of interest, too.

On another topic, I'm curious about the mixture of potting soil and sand you are using for your Grevillea victoriae. If you were to add sand to most Seattle-area garden soil (which tends to be clayey), you would end up with poorly draining concrete-like soil. I would assume that potting soil which already has perlite or something similar in it for drainage and would not need an addition of sand. Are you planning to move the shrub into the garden at some point? This is a substantial shrub--the mature ones I've seen are at least 6 feet tall by the same width. If you can find a place in the garden for it, it might fare better. As you probably know, plants in pots tend to be more vulnerable to extreme cold.

Date 2017-08-15
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May 31 2018 13:14:08