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Designers List of Shade Plants for Root Weevil Resistance

NE Portland Hostas with Root Weevil Damage

Root weevil damage distracts from an otherwise beautiful collection of shade loving plants.  

Designers List of Shade Plants for Root Weevil Resistance

I wanted to write a blog about shade plants for root weevil resistance. Root weevil disfigure so many shade garden plants and can make a garden look ravaged. It’s disappointing to see hosta and other plant leaves looking all chewed up. Can we design a shade garden with beauty and style without using root weevil favorite snack plants?

“Well HELL that’s not much of a shade garden” is what I said when I thought about eliminating all the plants root weevil like to eat. I was disappointed in the tiny number of plants that would work and wandered off to write about something different, something a bit cheerier!!!! However, I’ve been thinking about it and yes, we have some great plants we can use. 

Evergreen Shrubs  

Fatsia japonica Spider's Web in SE Portland Residential Landscape Design

Sometimes choosing an interesting variegated leaf, such as this Fatsia japonica ‘Spider’s Web’ can hide the notching caused by Root Weevil (look close!)

Aucuba, Daphne and Fatsia are not root weevil favorites and if you select the variegated forms the notching doesn’t show as much. To be specific, Daphne odora ‘Marginata’,  Fatsia japonica ‘Spider’s Web’, and Aucuba japonica ‘ Gold Dust’ are varieties that I recommend.

I have never seen much leaf damage on our Native Huckleberry (Vaccinium ovatum) probably because the leaves are so tiny.  

Three Root Weevil Resistant Rhododendron for Part Shade 

Grant Park Garden Design Rhododendron with Root Weevil resistance

The fuzziness on the bottom of the leaves on some Rhododendrons reduce Root Weevil damage.

I’ve found the official lists less than helpful since most Rhododendron listed are sun lovers. Root weevil prefer part shade to shade. 

Rhododendron ‘Clipiense’ is my best weevil resistant compact rhododendron for shadier situations. This rhody has fine hairs on the leaves so root weevil rarely bother it. It’s a slower growing variety and can take more shade than the other two I have listed but not deep shade.

Rhododendron ‘Fred Peste’ is a compact red rhododendron.  Fred does well in morning sun and afternoon shade, although he can take more sun than average.  

Rhododendron ‘Blue Diamond’ can take full sun but does well in full am sun and afternoon shade. It can get taller than wide.

Perennials   

NW Portland Sword Fern and Hardy Geranium in Residential Landscape Design

Sword fern (Polystichum munitum) and Hardy Geranium (Geranium macrorrhizum) do not show Root Weevil damage.

Sword fern (Polystichum munitum)  has a fuzzy frond (leaf) and root weevil don’t eat fuzzy leaves typically. Most fuzzy fronded ferns will be root weevil resistant and are an important player in a root weevil free planting. 

Hellebore argutifolius is perfect for NW Portland Landscape Designs

Helleborus argutifolius photo credit: Great Plant Picks

Hellebores are typically safe from weevil once they are mature plants. When the soft and munchable new leaves unfurl in February the root weevil have not hatched yet (here in Portland) so are not present until late April or May. The harder leafed hellebores like Helleborus argutifolius seem particularly impervious. 

Groundcover Plants   

Oregon Oxalis (Oxalis oregana) doesn’t seem to get a lot of weevil attention in my gardens and it is fun to add to salads. Same with our native piggy back plant Tolmiea menziesii. It has hairy leaves and is great for shade. For Saxifraga varieties, use the hairy leaved varieties for weevil resistance, the smoother ones are on the weevil munch list. Hardy geranium varieties that smell like cedar and have a fuzzy leaf are 100% weevil resistant – Geranium macrorrhizum for deep to moderate shade and Geranium x cantabrigiense for part sun areas. Another good bet is Sweet woodruff (Galium odoratum)

Last but not least, Euphorbia Rob’s spurge (Euphorbia amygdaloides var. robbiae) is a tough evergreen ground covering shade plant. I consider it a thug but it’s great to use in gardens where I have a path that doubles as barrier to their creeping roots. This plants roots must be contained or it will march right over your hostas. I’ve never seen any root weevil damage on this plant.

 Know Thy Enemy?   

Root Weevil have no natural predator here in the Pacific Northwest so it’s rare to find a shade garden without them.  We can cut the population of root weevil down to tolerable numbers and thus get our beautiful shade garden back. Read my blog “Attack of the Root Weevils”  to learn what can be done to reduce their population in your garden. 

 

Attack of the Root Weevils

Or Why you should care about root weevils,  and what to do about them once you do

Close Up Picture of the Root Weevil

I have noticed that most established shade gardens have visible leaf damage  from adult root weevils (see photo showing leaf notching). It is ugly, but it doesn’t kill your plant. The serious problem is caused by their larvae who eat the roots of your plants during the late fall and winter. It is very difficult to kill the larvae because they live underground nestled into the roots of your plants to be close to their chosen food source. Think of them as tiny, tiny zombies! Rooooooooooooooootttttssssssssssssss………..

So how do you know if you have a root weevil problem? Here is what I recommend:

Its the damage done to the roots that we worry about. We must control the adult weevil before she lays her eggs.

Its the damage done to the roots that we worry about. We must control the adult weevil before she lays her eggs.

Check your indicator shrubs for notching! These are Hydrangea, Red Twig Dogwood, Azalea, and Rhododendrons. Many perennials will also show the notched leaves such as Hostas and Coral Bells (Heuchera).  If you have only a few notches, you don’t have to do anything or you could treat once a year as a preventative measure.  If you have more than a few notches, we need to talk but you can also check out my blog for all the gory details of killing root weevils.  It is tricky to do.

Don’t bring them into your garden………Here is a timely tip, be very picky about buying plants on discount, or at fundraisers!  Look for notching on the leaves, and don’t buy any plant that has notching, or is near plants with notching. That means there are probably eggs in the potting soil that will hatch in your garden. You don’t want to introduce them into your garden.

Now the important part. How do you get rid of them?

The easy answer is, in the long term, the harsher one. The chemical products out there are either harmful to you or harmful to the bees which we need to keep our gardens productive and beautiful. Using chemicals to get rid of root weevils is definitively not the way to go.

I purchase living nemotodes that are specifically listed for root weevil. Properly applied, they will swim through your soil, enter the body of the root weevil larvae, and lay their eggs. The nemotode hatchlings will eat the larvae. Initially you will do this in both September /early October and the following May which are the ideal nemotode vs. larvae times!

The two  most important things ares that the soil must be warmed up and moist and you must apply the nemotodes must be applied at dusk, never in direct sunlight.   If we are having a cool May you may want to wait until June or call me and ask. In September you want to be sure your soil is well watered prior to the treatment of nemotodes, and then water well for two weeks following the treatment. This will eliminate some of the root weevil problem for 2013. You will have to repeat the biannual treatments for a few years to get the weevils properly controlled, and then continue with a once a year preventative treatment cycle (still in September OR May).

The good news is that it is really easy to do!
1) Take a 5 gallon bucket and fill it up with water.
2. Treat the water with a product called pondzyme (people use it to protect their fish from the additives in our water). I use 1 and ¼ teaspoons of Pondzyme to 5 gallons of water.
3) Add the nemotodes to the water.
4. Using a plastic pitcher I then water the nemotodes into the soil where I see leaf notching.
It is very little effort for a dramatic and healthy result.   Good gardening!

Resources:
Living nemotodes for root weevil larvae can be purchased now through September at: Portland Nursery
http://www.portlandnursery.com/
Farmington Gardens
http://www.farmingtongardens.com/
Cornell Farms
http://www.cornellfarms.com/
and other higher end garden centers.
Tranquilty Ponds has 3 locations and they sell an 8 oz bottle of Pondzyme for $26.00.  Remember you need the pondzyme to protect your nemotode warriors from chemicals in our water so don’t skip this step.  It is very concentrated so it should last you a very long time.    http://portlandpondsupplies.com/