Morning Glory, https://parkseed.com/heavenly-blue-morning-glory-seeds/p/01049-PK-P1/. and Cardinal climber, https://ferrymorse.com/products/cardinal-climber-vine?variant=7388602204208&gclid=EAIaIQobChMI8tX-w_OW4QIVE7aWCh2gEgDqEAQYBCABEgKIK_D_BwE, are two of my favorites. They both do have lots of seeds, but are easy to mow down or pull up.

Whatever you do, do not plant trumpet vine, Campsis radicans, you will never get rid of the tubers and they will show up 40 feet from the plant. At least they do here. After the apocalypse, the only things left will be cockroaches and trumpet vines.

Gardengal lives near you and should be by soon with some local ideas.

Unfortunately, other than the weedy bindweed type of morning glory, it seldom gets hot enough here in summer to encourage these to bloom. Dismal failures in the Puget Sound region!

If you want an annual vine, I'd go with one of the black eyed Susan's - Thunbergia alata. Grows fast and blooms hard until frost. If you want something more permanent, I'd consider honeysuckle (and our resident hummingbirds will thank you!). You could also do clematis.

A Cost Co near here had evergreen clematis in 5 gallon pots this week, in bloom and already starting to send out the yards long bursts of new growth these produce. If you are only covering 15 ft. one plant would do it. Otherwise an independent garden center near you should have multiple different possible choices.

Not gonna work in the PNW. Other than the bindweed, morning glories just do not do well here....well, they grow fine but just never flower :-) It just doesn't get hot enough here in summer for them to flower at all reliably.

Please try Luffa (Loofah) vines! They grow like crazy and have lots of beautiful yellow flowers the bees and pollinators love. It's an annual so a temporary solution to your problem but a quick solve. Plus you get the sponges at the end of the season! I used one summer to bring some life to the garden while re-landscaping.

Certainly throughout the PNW down to central OR - further south gets a lot hotter in summer. But west of the Cascades the climate is a modified Mediterranean with mild winters and cool, dry summers. Average summer temps are 75-80. Any temps above 90F are unusual and typically occur only a day or two at a time.

Wow. I live in central NH and my purple and pink morning glories grow and bloom like crazy as long as I put a little Miracle Grow on them a few times a season. The blue not so much, but there is a lot of competition because I have so many pink and purple and am trying to seed in blue. I am not much of a gardener. They are on top of a retaining wall and get sun almost all day long. I love them because they keep coming back every year and I hardly have to do anything. Our temperatures aren’t much different than yours. Either I have the perfect micro climate or they are wicked sensitive to a very small difference in temperature or some other aspect of the climate or soil.

2012 Edition of New Sunset Western Garden book has Ipomoea nil, I. purpurea and I. tricolor designated as being suitable for "All zones" - I wasn't aware that there was a problem getting one or more of these to bloom in the PNW. And am sure I have seen blue morning glory plants with flowers all over them from time to time in gardens here - by whatever means this was accomplished and whichever species these have been in each instance.

But I don't remember seeing any around here that were particularly large or lush, suitable therefore for screening.

My morning glories in central NH in full sun didn’t bloom until August for me. I would rather have things that bloom all summer If I am planting annuals. I live in a cool spot, though.

You could also consider medium shrubs as a choice such as blueberries.

I would never plant 'Grandpa Ott' again. While the flowers are pretty, they are too small to be exciting, and it has been the weediest plant. Still fighting sprouts 5 years since getting rid of it. Heavenly Blue is much better all around. Another great annual vine for quick cover is moonflower vine.

I am not at all sure why there is such insistance on morning glories to cover this fence!! There are scads of other quick growing annual vines that are much better suited to cool PNW summers. And that can guarantee flowering much earlier than the late August or September, when an MG might be persuaded to produce a flower or two here.

To be honest, I would much prefer to have a perennial vine for this purpose and there are no shortage of options to choose from. The Clematis armandii mentioned above is an excellent choice and is evergreen to boot!! And all manner of vining honeysuckles as well, most providing summer long color, fragrance and hummingbird attraction.

OP here. Thank you to all who are responding— I am learning a lot! I just want something that will grow as fast as possible, regardless of looks, yet not be invasive such that we create a headache for later.

I see morning glories are being debated, so is there any consensus I could choose Clematis instead for something quick growing by summer and lush for privacy? And how many plants one would need for that size fence?

The other ones I’m looking at are Passion flower or honeysuckle, but am not sure if they are a good choice.

You have to be reasonable in your expectations of fast coverage :-) Permament, perennial vines - clematis, honeysuckle, passion flower - will take some time to establish and fill in. But will be a better long term solution as they will provide better, denser and longer visual screening once fully establshed. And do not need to be replaced each year.

Annual vines may grow fast but have a much shorter functional life as a screening plant and will need to be replaced seasonally.

For 10-15' feet of fence you would probably need only one plant if choosing a perennial vine, as most will grow at least that large if not larger. But it won't hurt to plant more than a single vine if you want more complete visual coverage faster. You could plant one at either end and train them to grow towards each other or space out three equally along that distance.

If you opt for a perennial vine in multiples, make sure they are all the same species (not one each of the clematis, honeysuckle or passion flower) as they grow at different rates and with different vigor and one will outcompete the other(s). And any perennial vine available at your local independent nursery will work for this purpose....although some will work much better than others :-)

"I am not at all sure why there is such insistance on morning glories to cover this fence!!" Because Heavenly Blues are freaking gorgeous!! Been to Portland several times in summer and didn't think it all that cool. Just average. MG do not take all that long to flower, but the show is worth the wait. Still, not saying it's the ONLY thing. Just one good dirt cheap, fast option.

To clarify my OP, we have intentions of redoing our own backyard sometime next year (with a professional landscape designer that will likely take it out) but can afford a temporary/fast solution to serve in the interim. -- So a fast-growing annual would actually fit the bill here over patience for a perennial as it may very will be replaced early next year. My apologies if I didn't make that clear in the OP!

"Because Heavenly Blues are freaking gorgeous!!"

And so are large flowered clematis!! And with a much longer season of interest/flowering!

The PNW is known for its cool summers. Growing tomatoes here is a challenge as one has to pick very short season. cold tolerant varieties to get any hope of a successful or bountiful harvest. And some plants common to other areas of the country wth a similar hardiness zone do not thrive in this climate as it is either not hot enough for them to bloom well (eg, the MG's or crape myrtles) or to successfully ripen new growth to withstand winter (eg, loropetalum).

This really is a very unique climate area that is dissmilar to anywhere else in the continental US. That's why plant selection advice from those living in the midwest or east coast, where summer temperatures can routinely exceed 90F for days on end and with high humdity, tend not to be very practical or helpful.

This climate is far more closely related or similar to that of the UK. Not Florida or New Hampshire or Missouri :-) And like the UK, summer temperatures exceeding 80F for more than a few days at a time is considered a heat wave!!

Just now seeing you would prefer an annual vine, I'd suggest you look at hyacinth bean vine (Dolichos lablab), scarlet runner bean (Phaseolus coccineus), blackeyed Susan vine (Thunbergia alata) or cup and saucer vine (Cobea scandens). All grow very rapidly, flower early and continuously throughout the summer and all do well in our mild climate. But will need regular watering during our very dry summers!

I can vouch for morning glories not working well in cool maritime climates. Apart from the lack of heat and limited growth, MGs close if the sun isn't out, so they're shut quite a bit of the time in cloudy climates.

How about scarlet runnerbeans? Leaves, flowers and delicious beans.

Or hops? There's a golden leaved one.

But that fence really would look fabulous with Clematis armandii on it. Deliciously scented, evergreen and flowering right now.