Special weather blog for PDX gardeners

A watch for gardeners

There is a very interesting forecast for the Thanksgiving week going into and through the Thanksgiving weekend. A sharp cold front will slide down the coast from the Gulf of Alaska ushering in much colder drier air. There will be precipitation with the front Tuesday evening but it appears that it will dry up after the front goes through. This is typical of our climate where modified arctic air follows the front by a bit. It reduces our chances of snow. And if you don’t want truly arctic air you DON’T want snow cover. That would cause low temperatures to plunge.  So it appears we may dodge a bullet. I have read that this is not very El Nino-like. Well, I remember plenty of El Nino years with modified arctic air- remember that does not preclude us from having cold weather. El Nino affects the WHOLE winter not just the weather week to week. That is an important distinction to make.

A few freezes then a plunge. Is this El Normal?

The good news is that in our current regime we’ve now had two freezes/frosts in the city and considerably colder in the out lying areas. That means that plants have received an early warning and will have hardened off a bit prior to this next wave of much colder air. This is good. By the way, early freezes/November events have happened in the past and they can be pretty devastating- I don’t expect that. (For more information see November 1955 as well as 1985- when each entire month was frigid and temperatures plunged to the teens and lower-horrible for plants.) So, this looks like a fairly typical cold snap. What is interesting about cold Novembers is that the rest of the winter is mild/normal 80% of the time. Its entirely possible- and it has happened many times in the past that this cold weather is our coldest of the winter. That is by no means a forecast but I can say that I’ve seen that many times in the past. Don’t think that this is what the rest of winter will entail- it may or it may not.

Normal weather progression with a buckle

Ridges and troughs that move along the jet stream give us weather in 2-3 week segments and following the wet part of this month it is completely within the realm to have it followed by a dry period. What is different about this switch is that there is a high pressure system in the North Pacific that has moved to the west (this is called retrograde because it is a reversal of the normal movement from west to east). This buckle in the jet stream reflects a conveyer belt moving north to south. Its bringing air directly down the coast. By the way, modified arctic air is just that. Air from the arctic that has moved over relatively warmer Pacific waters. The layer of warm/wet air at the surface mitigates the pure cold air and it is modified- it loses its pure arctic punch.  If the air were arriving from the northeast/east that air would not be modified by the waters of the Pacific. That would be worse. But stay tuned for #2.

Cold air pool- air pools east of the Cascades ROARS through the Gorge

A large area of cold high pressure sets up following the front Wednesday and beyond.  This will increase  the pressure gradient from east to west as the cold dense air pools in the Columbia basin east of the mountains. North/Easterly winds will roar through the gorge- this is called an outflow (or a Bora wind)  and reinforces the cold air. Starting Wednesday night these frigid winds will spread across the metro area. It will depend on the amount of snowpack east of the Cascades (for instance the Pendleton area) that modifies the air to be colder on how cold it will ultimately get in Portland. I generally worry when the temperature in Pendleton is below 15ºF- that is a really cold air source and it is somewhat of a benchmark for how cold we will be. Right now Pendleton is forecast to have a low in the low teens.

Our predicted temperatures:

As of now temperature look like in the northern Willamette Valley they will definitely be in the 20’s with some spots in the high teens. Luckily, highs will be above freezing in the upper 30’s to low 40’s and thawing should occur to some extent each day.  Be aware that wind is a double edged sword. Wind not only transports cold air it also stirs the atmosphere from stratifying cold- it produces mixing. That means that wind keeps the temperature warmer- but it will still be below freezing and that causes damage. Therefore, it may only be 28ºF at the airport but a 35mph wind can cause a lot of damage to plants. I estimate that situation would be the equivalent of 18ºF in still air.  That is how zone 8b (15º to 20ºF) plants can be damaged at warmer temperatures. Away from the Gorge temperatures will ultimately be lower without proximity to wind (wind sheltered sites) and actual lows in the upper teens will cause the same amount of concern as our (relatively warmer) temperature. Ya’ got it?

Dew point- watch the dew point carefully

Arctic air is cold, dry, and dense. So much so that it almost hugs the ground like a liquid and flows thusly. An outflow wind is a product of this dense property. Dew point is a measure of the moisture content of a parcel of air in the atmosphere. The lower the dew point the drier the air (By the way relative humidity is determined by the dew point- it is relative to the amount of moisture at any given temperature).  Arctic air has very low dew points- its freakin’ dry air. That dry air in concert with low temperatures causes damage to plants and wind exacerbates this. Think of arctic air + wind as a torch in the opposite. The immensely cold dry air sucks the moisture out of leaf surfaces and in combination with freezing causes damage to such things as broad leaved evergreens that don’t go as completely dormant as say, deciduous plants. Dew points below 12ºF and subfreezing temperatures spell danger for many borderline plants.

What kind of plants will be damaged?

Tender plants (zone 9) will be very challenged and most likely die. Plants that are still in active growth will lose that new growth to the freeze. Hardened off older foliage should be fine. Zone 8b plants (15ºF) will be damaged but probably not die- those in wind sheltered spots will fare better. This will likely NOT kill or marginally injure Phormiums. That should give you context for past cold waves/years. One slight amount of luck that can be good is that we’ve had a very warm summer which hardens off the wood of semi-tender plants. One bad thing is that we had the mildest October of all time. See how confusing this can be? Protect containerized plants if they are not hardy below 15ºF. Water containerized plants that are hardier than that. It appears that the real wind/cold goes from Thursday morning to Saturday. Then slow modification. If I may be allowed to geek often the coldest night of Portland cold snaps is the last night. That is because winds have slackened off and radiational cooling in the calm stratified air takes hold. So- the wind is good and bad.  But be wary of calm air as well.  There is still time to apply mulch and protective covering but make sure it is in place by Wednesday evening.

**** Wait and see***

The NOAA and other sources are very much on board with this forecast. I’ve noticed that their forecast ultimate lows have been very conservative. This is a good sign. However, I’ve seen this weather regime before and thats why I’ve prepared this post.   I’ll update it as things progress.






Special weather blog for PDX gardeners

To Tidy the garden or NOT.

November. Pretty much.

Today was a blasting, chinook, classic stormy November day in the PNW. The wind blew gusting to 40 mph  for a good 12 hours straight and the rain came down in sheets. Once the cold front swept through this evening I took time out to survey my garden. I was a little wary because there was a stupid ‘Paul’s Scarlet’ Hawthorne that had been split in half at the end of my block from the swirling winds. (Of course it broke where heart rot had whittled away the interior- that seems to be the case in about 75% of the tree failures that I see. ) What I found was not damage but the garden definitely looked like it had been through the wash. Best of all the leaves had been stripped off of ALL of my deciduous trees and flung far away. In this frost free autumn, I was curious to know when they would go.


Leaves, leave the leaves

Recently I read an article saying that it was more environmentally sound to leave leaves rather than rake them up. It touted all sorts of benefits and all I could take away was UM, NO shit. There has to be nothing more idiotic than stuffing bags full of leaves to be hauled away. A phenomenal waste of time, energy, and money. (Even more hideous is when the leaves are ensconced in PLASTIC bags….never to decompose and forever stuck in landfills.) Leaves are good. They are designed to go away. Thats their whole reason de etre. And they break down into all sorts of wonderful things like leaf mold, compost, and soil. True some leaves take longer to break down than others but for the most part they all go away in a reasonable amount of time. I take the leaves from my trees and the neighbors contributions and use them to mulch my beds. They do all sorts of great things, like protect the soil from frost heaves, encourage biological activity and save me money the following spring on compost. I try to move the leaves to the edge of dainty perennials and bulbs leaving their crowns exposed so they won’t smother. Some plant that get that treatment are Cyclamen coum, Tommy Crocus (Crocus thomasinianus) and small scale ground covers,  (Ellisiophyllum, Pratia, Veronica liawanensis) and remove them from evergreen Sedums.  Other than that I use them to cozy up to such perennials as Astelia nervosa, for added cold protection and I tuck them under the leaves of evergreen Epimediums for the promise of spring.  So, is it environmentally beneficial to leave the leaves and let them break down? What do you think?

Rock steady

This first wet month of winter (technically in our region) often comes with gales. After a good blow its a great time to check on shrubs that may have rocked in the whipping blast combined with saturated soils. Go around the garden and give a wiggle to any fast growing, relatively new shrub or tree. If you see something listing to the left there are several things that you can do. First I check to see if I can right the plant and then give it a good stomp on the loosened side of the root ball. Don’t be bashful (also don’t stomp so hard that you tear the roots) but give it a good firm push. Normally that will work magic and you are set. Keep your eye on especially fast growing shrubs such as Grevilleas, Arctostaphylos, Italian Cypress, Arizona Cypress which can get a little over enthusiastic here in their eternal spring. If you have to stake the plant then so be it. I use rebar for the bigger things and 6mm by 2mm x 1m  metal stakes for smaller things. Thread the stake through the middle of the shrub (candidly hiding it from view) and then attach it with velcro straps (garden velcro is magic- if you don’t know it you should).  When everything is staked in a sturdy manner make sure to check back and loosen the velcro if growth warrants it. Most often this situation and boisterous growth will set things right in a season or two. If stakes are not in your palette then consider a big rock on the loosened side of the root ball. Rocks as all gardeners know are magic.


In the last 15 years Greg and I have made extensive mental notes about how to grow a huge amount of plants. One thing that we can say unequivocally is that gardeners are too tidy. A mild fall day that coaxes the gardener into “clean up” can spell doom for many plants. And there is scientific hoo haw to back it up. First of all many perennials go through a process of dormancy that can trick the gardener. Top growth loses leaves and looks withered. The first instinct is to cut this off. On many plants this will spell doom. If you look carefully at a plant, Agastache for example, you will notice a low dome of foliage that erupts at soil level below the “dead” woody structure in autumn/winter. What isn’t evident is that what looks like withered stems is actually a form of protection for that ground level winter season set of foliage. The tracery of stems mitigates the coldest temperatures and the semi-woody hollow stems can  provide a source of oxygen to the roots- very essential in our winter saturated soils. Cutting this away exposes this fresh growth and interrupts this dormant status. I’ve done it, Greg has done it and when the first freeze hits-  the exposed dome of semi-dormant foliage is destroyed. This spells doom for the plant. It may look messy but resist all urges to cut the top growth on these following perennials until all possibility of freezing weather has passed- that could be mid-April. Salvia greggii, Salvia x jamensis, Salvia muelleri- pretty much any semi-woody Salvia, if you have any doubts don’t do it. Agastache. Stachys coccinea, Antirrhinum sempervirens are just a few. We are convinced that people are losing these perennials from this kind of over enthusiastic tidiness and then they are proclaiming the plant NOT HARDY.  So try it and you will see. Penstemons, Scutellaria, Zauschneria (Epilobium), Dicliptera. So if you have lost these plants in the past. Just do nothing until all danger of frost has past. If you are a neatnik and you can’t handle this there are some boxwood that may peak your interest.

If you simply must

There are some plants that you CAN cut back in mid winter and they will shine when the time comes. So now that I’ve taken away your winter tidying fun I will give you a list of perennials that definitely benefit from some grooming. Hellebores x hybridus, Epimedium, Ferns, Beesia, Heucheras, There: that should give you something to do.

The weather

So far we are having a very NORMAL November. The polar jet has been going strong despite the continued strong El Nino. After our scorching and dry summer we should all be happy to see moisture again. In the next month there doesn’t appear to be any surprises in the offing. If there is a change in the forecast then I will chime in.  Until then. Happy Thanksgiving from Team Xera.




To Tidy the garden or NOT.

The Ultimate Pest Control: Diversity

IMG_0241 IMG_0156

A little helpful information:

Gardening in our climate is not just about the weather. Pests and diseases can interfere with our personal Eden. Since the weather has slipped into boring November mode (as opposed to exciting November mode) I thought I’d pass on a few observations that I hope will add to your gardening knowledge.

Yer really buggin’ me

For the most part avoiding plant pests is easily 75% dependent on correct culture. We all know that if you don’t want aphids you should probably avoid Roses. The healthier a plant is the less it will be bothered. Grow plants to their ultimate cultural requirements and that is the ultimate pest control.  But several excellent plants are afflicted and for the most part they shouldn’t be chucked out completely.  Hellebores are one such perennial that inevitably suffers aphids. They almost always do and though it can be gross to us humans there is an easy solution. Do almost nothing. OR spray the aphids off with a strong jet of water. I have found over the years that resorting to poisons is a worthless, costly, and dangerous way to spend your time. The plant industry is heavily founded on the predication that gardening is a problem that needs to be solved. They will happily sell you any kind of dangerous concoction to fling about your beautiful space. The truth is: its not necessary. So, in the case of Hellebores- where the aphids do almost no damage, either spray them off with water- they are soft bodied insects and this will damage or kill them or do what I do. Simply ignore them. By winter when it is time to cut back the foliage to make way for the flowers the aphids will have disappeared. POUF!

Protect the predators and you will win

Lady Beetles (Lady Bugs) – especially their larvae eat aphids. They should be encouraged to proliferate. By the way, the larvae look like little black alligators. They cannot fly and scramble around the plants foraging for aphids. Even Yellow Jackets will consume aphids so they have in part some reason for existence. Ants will farm aphids- they will actually physically move them to the soft  tips of the plant. Aphids are born pregnant by the way which relates to their seemingly overnight increase.  Don’t go killing the ants- again spray water or squish the aphid populations at the tip with your fingers and you will have progress. There are various other critters that can make a home. Luckily, in our climate- unlike the east we do not suffer Japanese Beatles or other voracious things. There are exceptions and they do turn up from time to time. An example is the Marmorated Stink Bug which has recently leapt to our shores. It tends to gather in great numbers on specific plants. You can easily identify this guy – as opposed to other shield plated green stink bugs by the fact that it is brown and the prominent antennae are striped horizontally. They are attracted to felty leaved things such as Clerodendrum and Paulownias. For the most part they do very little damage other than to mass and gross us out. Already their numbers are declining from natural predation. They can cause problems for home food growers- a topic of which is outside the scope of this blog- flowers man, its about flowers. So, it should be obvious that spraying poisons kills the good guys as well as the bad. No need to upset the balance and cause potentially long lasting harms. Let it be.

Slugs piss us off

Slugs (and snails) can be a real pain on attractive plants and they are part of the cost of doing business in our region. Personally, they are not a huge problem in my garden because I now avoid plants that call them in. Hand picking slugs in the evening on susceptible plants is one way to lower the population. It may seem futile, but trust me the amount of damage that a single slug incurs is more than you think. Many slugs spend their  day time in the soil beneath the plants. Mulch and tidiness are a great help here. Cultivate the soil gently around Hostas and you will find the hungry culprits. Slugs are especially damaging to plants that are just emerging. Focus your energy there and the plant once up and growing can withstand attack.  There is slug bait which can work very well if you are persistent. Sluggo (TM) is not toxic to pets and it does work- but it must be applied constantly- preferably in mid spring and though slow it really will put a dent in the population. As an aside in the past I have used metaldehyde (Deadline) when the whole gastropod thing was totally out of hand. The ONLY way to use it is to put it in the bottom of a bottle or jar and lay the container on its side. The bait will lure them in and the container will protect pets who are also attracted to the lethal goo. Simply discard the container when it is full of slug holocaust. Snails are just as pernicious as slugs and hand picking is surprisingly affective. You can also make traps. One way is to take a 2″ x 4″ and pour beer on it. Then prop it up with two bricks. During the day the snails and slugs will congregate in the shade on the underside of the board. Simply pick and dispatch the offenders.

Some perennials that are resistant to slugs: Geranium, Dicentra (Lamprocapnos), Epimedium, Vancouveria,  (The Hosta cultivar ‘June’- shows remarkable resistance), Oxalis oregana, Ferns (nearly all), Euphorbia rigida, Cyclamen coum, Hybrid Hellebores.

Stupid little notches

The Strawberry Rootweevil is a pest that shows its presence in several different ways. Most conspicuously notching of the leaves of broad leaved evergreens is a sure fire indicator. As an adult the shiny black 1/4″ long weevils are surprisingly slow and dumb. They are active at night and I’ve gone out and shaken the bushes to watch them drop lethargically onto the ground. Put a pillow case under the shrub and do this and then simply squish the dumb things. They move pretty slow. More damaging is the larval stage. They insert themselves into the root mass of plants and feed. Obviously strawberries are one of the victims but I have found them on nearly everything- perennials, shrubs etc. They may feed so heavily that the plant collapses or loses enough root mass that it appears drought stressed. By then its too late. But there is great control with predatory nematodes. This should be applied as a liquid. They come on little sponges (avoid exposing the sponges to large swings in temperature) Simply place the sponge in a watering can and then pour around the base of the plant. They require liquid to travel through the soil so don’t let it dry out. Weevils seem to prefer dry shade conditions. Regular watering and mulch and healthy plants appears to dissuade them.

The soil giveth and the soil taketh away

Nothing is more disheartening than having a plant up and croak. Believe me it happens to ALL gardeners in ALL gardens. Often it is a complete mystery and the best way to deal is to simply move on- plant something new and commit the dead to the garbage. It could be culture, it could be the way the plant was raised to begin with, its possible that an errant gust of wind rocked the plant and tore the roots. No reason to over think it. Here are some culprits that really do warrant attention.

I’m rotting, I’m rotting.

In our region there are two soil borne pathogens that really can wreak havoc. They are Phytophthera and Verticillium (wilt). They are either present in your garden soil or they are not. Phytophthera is almost universally present in my experience. It causes root rot and it can seemingly snuff out a plant in a day or two. It forms masses of threads in the soil that are tiny – don’t go trying to locate the threads- and the spores travel through water in the soil. It can be introduced from moving a plant (with minute amounts of garden soil on the roots) from one garden to the next. But as I said, chances are that it is already present. It is greatly exacerbated by over watering or watering when the temperature is high. A plant may  live happily and then simply collapse in a short period of time. I wish there was a comprehensive list of everything that is susceptible- and there are many things that are not- but with so many zillions of new plants on the market I somehow doubt they would all be covered. Plants native to summer dry climates are the most at risk- as well as drought tolerant plants to begin with. Here is where culture and plant origin dictate how you grow them. Avoid watering a drought tolerant plant on a hot day. ( Watering to establish a new plant is different- water until you see new growth, then taper off)  Some plants that are susceptible are our native Chamaecyparis and its millions of cultivars. (Chamaecyparis lawsoniana), Grevilleas, Ceanothus, Arctostaphylos, Cotinus- you see a pattern. Here is a little more information that I found:

“Plants typically die from phytophthora dieback at the end of summer when the plants are under the most stress. For this reason phytophthora dieback can often be confused with symptoms of drought. Phytophthora dieback will affect a range of different susceptible plants, but will not impact on resistant plant species. If the disease is suspected, a likely mode of disease transmission should be identified. The best method to confirm the presence of the disease is testing of soil and/or plant samples by a diagnostic laboratory.”

Skip the laboratory. Do not over water drought resistant plants- in this case that CAUSES stress. And I have found that even a small amount of water on a hot day can spell disaster. Instead, rely on a plants natural adaptation to dry conditions. Let the plant rely on all that falls from the sky. In winter when soil temperatures are cool Phytophthera is not an issue. If a plant succumbs to this you can choose to NOT replant with the same thing- if your Daphne croaks, do not plant another Daphne there – thats just common sense. Try for a completely different genus. Experimentation and diversity are the key.

I’m wilting, I’m wilting.

Verticillium (wilt) is also present in many garden soils. It manifests itself differently. Instead of taking out the whole plant- it does it in irritating stages- Its hallmark is one dead branch at a time. This too has a long list of plants that are susceptible and a list of tolerant plants. Verticillium infects the tissue by plugging it with mycelium spores on the interior wood- girdling one portion of the stem at a time. It is known as a wilt because that is how it presents. Japanese maples are frequent victims as are Hebes. There has been some success in using well composted mulch to diminish its affects. Dormant in the winter it arrives with the warmth of spring. The best recommendation I can make is again to plant for diversity- if you are replacing an afflicted plant- remember to make it a different genus. If your maple is affected consider a Crape Myrtle, they are resistant and one of the reasons we grow them. Other good choices are Nothofagus antarctica, Trochodendron aralioides, Eriobotrya japonica, Gingko biloba, Metasequoia glyptostroboides, Ceanothus and Feijoa.  Once again, this is where diversity is your friend. Monoculture- as we know has its drawbacks. Think differently. If you do choose to mass a plant take a moment to find if it is resistant. Again, as with Phytophthera a stressed plant will be the first affected. This is where grouping plants together with similar requirements pays dividends. Dry with dry, wet with wet. I have seen plants recover from this- prune out the affected tissue with a sterilized pruner and make sure to sterilize it again before its re-use. Use mulch to moderate the ground moisture and temperature. Avoid stressing a plant.

Diversity leads to a healthy garden

The key to avoiding pests and disease is through diversity in our gardens. Pay close attention to the ultimate cultural conditions of a plant. Consistency is also a healthy way to approach growing plants. Group those with similar requirements together. It all comes down to having a plan. That may be easy to say but less easy to live. If a plant succumbs to a disease- do not plant the same genus- move on. The greater diversity of plants in your garden the less likely you will suffer devastation by pests and disease.  A good garden steward knows how to roll with the punches. Pests, disease, weather are all part of the great outdoors.


The Ultimate Pest Control: Diversity