There's ALWAYS enough natural light for plant growth to start. Soil temperature is the primary limiting factor in spring, but once soil temperatures start rising above 55*, light can/does play a more significant role as a potential limiting factor of growth rate.

E,g.: If all potential limiting factors except light and soil temperature are static and perfect, a plant in 55* soil at the vernal equinox might grow very slowly. Increasing photo-period or photo-intensity won't do much to increase growth rate, but increasing the soil temp to 65* will - at which point soil temperature is no longer the limiting factor - low photo-exposure is).

At the summer solstice, a plant's growth rate in 65* soil should be at peak or close to it. Reduce the soil temperature to 50* and even in perfect light and ideal ambient temperatures, growth rates are likely to plummet to near 0.

You can read more about limiting factors by clicking on the embedded link.

Al

Lovely link! and highly relevant as the Seattle garden is in containers. I have no trouble at all with the basic concept of limiting factors.

So, maybe the question should be rephrased. At what point in the spring does Seattle soil warm sufficiently for good plant growth, and how much can this be accelerated by passive measures such as row covers or cold frames?

It is my belief that in Seattle, the cloud cover makes it much harder to get an early start than we find in some of our other (MI?) regions that are nominally a couple of zones colder.

E

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A close re-reading of Coleman's _Four Season Harvest_ does seem to substantiate the idea that sunlight may be contributing heat as crucially as light ("the determining factor is the effect of the sun rather than the temperature of the air. As the days shorten, the sun's path is lower in the sky and there is less solar radiation to heat up the frames. Once the sun's path is low enough, there is a period of about three months... when the gardener's only work is harvesting..." (p. 92)

Nope, not the cloud cover. Western Washington springs are very cold and damp and that is what slows plant growth, not the cloud cover or short days. Soil here, in spring, is fully saturated, even after a relatively 'dry' winter, and wet soils are cold soils. Our proximity to the eastern side of the Pacific Ocean basin keeps things cold in spring too - cold upwellings from the bottom of the ocean hit the west coast of the continent and keep things cool. Spring is cool, summer is late, fall is fantastic, because the upwelling slows seasonal warming.

Anything that increases soil temperature will increase plant growth. Planting in raised beds for better drainage is one way. Using black plastic pots to absorb whatever solar radiation there is, is another. Remay for frost protection. Clear plastic mulches to warm soil. Cloches and wall-o-waters for added warmth. Sloping planting beds towards the south, so sunlight hits the soil at more of a 90 degree angle instead of a lower angle.

West Coast gardening is very different from anywhere else in the country. Nation-wide gardening references are not very useful here. For the PNW, you really need either region-specific references, or British books as their climate is similar. So, good you came here for answers, but don't expect the books that work in MA to be relevant for Seattle too.

I don't plant peas until March or April, myself.

The growing season here is over 200 days. Last spring was abnormal. I seriously doubt that there is anywhere in the northeast that has a longer growing season than the maritime northwest. What dawdles or even fails here is kinds of plants that need a really hot summer climate, ubiquitous example the tomato plant. But specifics of how a planting of this is handled (variety and site selection, timing etc.) are what make or break it, and not just the climate.

Here is a link that might be useful: Sunset climate zones: Western Washington

E - I'm far removed from you, but I wait to put most bedding plants and plants not known as cool weather crops in the ground until soil temperatures reach 55*, which usually occurs here between May 20-May 30.

Sure, absolutely, the impact of passive solar gain on soil temperatures is part of the overall picture, and anything you can do to supplement the increase in soil temperatures will be helpful to the degree that limited light (or some other limiting factor) allows.

I don't think we can unequivocally say that light is not or can not be a limiting factor. As soil temperatures rise to the degree that some other factor is most limiting, we cannot eliminate light as one of the possibilities. In fact, the better you are at making all other (than light) potential limiting factors as close to perfect as possible, the more likely it is that photo-exposure will be limiting.

Al

If 2010 was abnormal, that's happy news!

I figure Gardenweb PNW is probably my best source for PNW gardening, and I also read the Territorial catalog. The Seattle gardener has some local resources. My other Seattle (OK, Port Townsend) friends were very careful about choosing adapted apple varieties but didn't get any set this year. My main contribution has been to suggest cool season crops - seems like maiche should be a real winner based on what I've heard this year.

What about spinach? Spinach is difficult over here, my CSA farmer tells me, because it wants to bolt before it can get enough nitrogen from the cool soil to really produce. But it SHOULD be real good in the PNW right?? I'm just baffled because I have a few years' experience with Coleman's 4 season harvest, and really thought an earlier start should be possible in the PNW.

Wait, what?? Sunset zone is 5? Isn't the USDA zone 7, for Seattle?

It's true that I don't use Sunset here in the east because it doesn't work well here - even their New England volumes are all redwood decks and yuccas.

Down here, we typically say April 28th is Tomato Day...
but the past two years we've had slow, cool, wet Springs. I put my peppers in the ground
on May 1st last year, and the rains and the slugs nearly destroyed my entire crop.
Next year I'll probably wait until the end of May, so the soil can warm sufficiently.

My friends, even at higher elevations, had better early crops by using containers
and capitalizing on the easier to warm small soil volume.

Josh

Seattle is USDA zone 8. Olympia is USDA 7. Most every where else in the Puget Sound area is USDA 8.

Sunset zones are entirely separate. Olympia splits between 4 and 5 depending on proximity to the Sound. I don't know about Seattle. Probably some combination of zones 4-6.

Cool season veggies like peas, spinach, some greens and most brassicas can be planted quite early here, often around the beginning of March. They don't seem to mind the cool soils and cloud cover has minimal impact. Poor drainage or overly saturated soils are definitely a limiting factor but quite possible to get around. Growing in containers is one excellent way to accomplish - raised beds another. Both will offer soils that respond faster to warmer air temps as well - they will heat up faster than regular landscape soil. Personally, I wouldn't bother with the warm season plants like tomatoes, peppers, corn, etc. until June, although many gardeners start them early indoors and then plant out once both soil temps and air temps are appropriate, which is usually around the beginning of June. Earlier, they just sit there and do nothing......or chill off or rot :-)

Most of the community farmer's markets start sales in April (if they are not open year round) and early/cool season veggies are often the first harvestable crops available so that might provide some indication of how early some crops can be planted, although not all are necessarily grown out in the weather unprotected :-) FWIW, my dad had spinach growing pretty much year round in his Seattle area veg garden and routinely planted peas on the traditional Washington's Birthday marker.

The best resource I have encountered for vegetable gardening in this area is the Maritime Northwest Garden Guide published by Seattle Tilth. It provides a month-by-month guide to veggie gardening in this area. Most local garden centers sell it or you can order online.

Here is a link that might be useful: Maritime Northwest Garden Guide

Hello Elizh,

I used to garden at the University Heights P-Patch on U Way and 50th NE until very recently. The general wisdom around here is that snow peas should be planted out around President's Day. These are a fairly cool weather crop, so I don't think you need to take extreme measures to have them germinate and grow at that time, in the past I just covered the planted spot with row cover fabric (mainly to keep the birds off, this is important!) and removed this when the pea vines seemed to be getting too big for it. I find that slugs get a few of the plants, but usually they grow fast enough that the slugs no longer want them, or cannot hurt them seriously. However, some slug bait might be a good investment this early in the spring. You can make simple hoops out of heavy gauge steel wire (a pair of pliers with a wire cutter is enough to handle it) and put the fabric over that to form a rudimentary super-low tunnel; but just draping the fabric on the ground works OK as well. I imagine that using clear plastic instead might coax the plants into growing faster, but I think peas are pretty easy to grow without that much protection.

I believe a lot of spring crops such as coles or salad greens are planted out a week or so after this. Scallions/onions etc. probably can be started around that time too, but I am not sure because we've always grown them from transplants.

As for heat loving vegetables such as tomatoes or peppers, they need more help. The last frost date in Seattle is April 20, and as far as I know it's not worth transplanting seedlings out before then. If you want to grow tomatoes early, you can plant them out after April 20 inside a low tunnel, which I have covered with cheapo landscaping plastic. If you don't want to build a short tunnel you'd probably best wait until Mother's Day (May 15?) before transplanting tomatoes etc. (and use a season extender such as a "wall'o'water"), which is what a lot of people do. Low tunnels are actually pretty easy to make, but they can be more trouble than some people want, and if you are not careful they can cause problems such as over heating or fungal disease.

Beans can be planted in early May IIRC, as long as the weather is not especially cool. I have planted them under clear plastic in the past to help germination and keep the birds away (row cover fabric is OK too, just remove when the sprouts seem to be established). As with peas, slugs tend to attack them, but if they grow fast enough they survive this without much long term effect.

You can plant squash from seed in early May as well, but be sure to plant them under clear plastic to warm the soil up and help germination, and keep planting after a week or so if none appear to germinate. They have to be planted out early as seed, and do not like to be transplanted in my experience. Last year I couldn't get mine to germinate after one try, so I tried to grow them from transplants and put them out later- I ended with vines but no squash as a result.

Cucumbers are similar to squash (don't like to be transplants) but they need to be planted three weeks later or so; they are very sensitive to cool weather and can be hard to grow here, but if the vine gets established you'll get some OK crops by August in my experience.

Anyway, if you want to have reliable info on planting times and the like, the best reference is the Seattle Tilth's book Growing Vegetables West of the Cascades which is divided into sections for each month, and lists the crops than can be planted during that month at the end of each section. I think it's worth the $15 price.

I think you've confused the title of Steve Solomon's book with the Tilth guide referred to in the preceding post.

Yes, you're right. I got my two main gardening books up. Growing Vegetables West of the Cascades is a book by Steve Solomon; among other things it has useful info on specific crops grown in the PNW. The book I was thinking of is the one referred to by Gardengal48. It's the best reference for when to plant stuff here as far as I know.

My favorite soil warmers are TunLCovers. I have bought from the manufacturer, but I get them now from Gurney when they have an offer to buy $50 and get $25 off in February. I haven't noticed damage from heat, usually the plants love it, including the weeds. You can push the plastic up the ribs for ventilation if you want. If its going to be unusually hot I can just take them off, too. I have to take them off to water anyway. They are double-walled plastic, which might make some difference. Also they are only 18" tall so by the time tomatoes are big enough to start blooming I usually have had to take them off. This way I can reliably grow tomatoes in the 72-85 DTM range but above that I may not get fruit until too late to really get a good crop. Of course here with the cold night temps all summer the DTM may be more like 115-125 days. That's why getting those mid to long season tomatoes out in April really makes a difference in getting ripe fruit. The early plants bear consistently earlier than those planted later. I also grow some early tomatoes like Juliet, Oregon Spring, Siberian Pink, and Verna's Orange Oxheart so I start getting tomatoes earlier. After last summer's cold temps I am cutting back growing tomatoes a lot this year though, and growing more beans and greens.

The really neat thing about the tunnels is they also can be used to dry out the soil for planting as they keep the rain off, so I put them out for a couple of weeks before I want to plant. I used to wait until April 15 to plant tomatoes but found a 30-year weather report and there is only a couple of degrees difference between then and April 1. I start seeds under lights in late January to February and start planting out about April 7, or when the plants hit the lights at 11". I just have to have some dry time to actually dig holes as I plant, and I put fertilizer and compost into the planting hole. I bury the plant up to the bottom leaves so it will only stick up 6 or so inches, then the tunnel boosts the temperature during the day and also at night. I've had frosts and snow on the tunnels with no harm to the seedlings. Since the tunnels keep rain off I need to water sometimes, and I also use Iron Phosphate snail bait under them as slugs like the plastic.

The soil is just too cool here for peppers and eggplants, so I do plant them in pots to keep the roots warmer.

I get great results setting squash and cucumbers out early with them too, which I start 6 weeks before setting out- with the tunnels I can start them in April, without I would start them about May 1. The squash plants really love them.

I haven't had good luck with spinach either, I'm glad to hear why. I do like to plant winter hardy coles like overwintering broccoli, turnips, and wild red kale by July 15 so they get big enough to live through the winter, then I have early greens the next spring. One year I had great bok choy planted in July as a fall crop, too. Chard, collards, and mustard do very well here as well.

Unfortunately, I also tried tunnels over pea and fava bean seedlings, in an area I had grown pole beans for a couple of years. I guess it had built up a big vole population. I pulled up the tunnels to check on germination and the ground was just churned with vole tunnels going up and down the entire bed, only about 3 peas managed to come up. I do succeed with peas planted in March in a box with hardware cloth in the bottom.

loads of excellent info, thanks to all!

I have rarely calculated my actual days to maturity, although I record seed starting, transplant, and the occasional first harvest dates. Although it would be particularly valuable here (MA) for fall crops. It took me a while to get the hang of planting them early enough -- it was so counterintuitive to sow in the heat, until I noticed the foxgloves and forget me nots popping up after a big rain in July or Aug. My favorite mistake now is to transplant Savoy cabbages too soon in the spring and have them bolt from frost stress. I think they must be less frost tolerant than other cabbage types - probably better in your climate. I wonder where spinach is really at home, climatewise...

oh - what are you using as a baseline for days to maturity, hemnancy?
how about the Territorial catalog?

Hemnancy, where do you live? I live in Portland and have great pepper and eggplant yields.

I planted all my greens in February and by April I was eating salads from my garden.

Unlike most everyone in the northwest, I also had a HUGE crop of tomatoes that I could not even keep up with them. Big ones, little ones, yellow ones, green ones! I would post a photo of one of my weekly yields if I knew how to do it on this forum. I think I owe my success to organically fertilizing with vermicompost and diluted fish emulsion.

From time to time I've heard folks talk about how you can plant peas in February. Well, you can, and they will survive for the most part. But they germinate and grow so agonizingly slowly it's best to wait another month. When they grow that slowly they're not much more than slug appetizers. Not to mention the soil critters that feast on the peas and their roots.
I figure the growing season here in Canby (south of Portland) is 150 days max. The last frost us usually not much later then May 1st, and by October 1st the light levels are too low for anything to grow. So you get May thru September.
I had a friend who used to live back east comment that the growing season here is not ended by a killing frost, but rather by light deprivation.

Western valleys: 150- to 250-day season; warm days, cool nights; length of season may vary from year to year

Here is a link that might be useful: Growing Your Own

Speaking for Seattle, snow peas do grow very slow in mid February, but I have not found that the slugs kill them off, and I think you still get the same crop of peas earlier than you would if you waited one month. The best bet is to put them under fabric or plastic... unless you're really unluck and get a pest infestation attracted by the warmer ground, it should work.

Towhees go for recently sprouted pea seedlings. If you find the new tops lying there with the pea part removed, you are feeding a bird.

We made a raised bed last fall with hardware cloth on the bottom and hoops with bird netting over them so I can finally have a mole free area to grow smaller plants; peas, spinach, strawberries, etc. I just couldn't get them to grow well with the moles tunneling everywhere else. The netting will keep out the birds and deer too, so it may be my most productive growing area. I may put plastic over the hoops to warm it up more since I don't get sun all day long because of the mature trees.

Serious home vegetable growers I know use plastic tunnels a lot. In addition to a cool climate you have to deal with carrot flies and cabbage butterflies. Excluding the adults with row coverings prevents the larvae from spoiling the crops.