Hi Paul - The soil may be deficient in phosphorus and I would suggest a Bloom Booster fertilizing nutrient application that has a high phosphorus NPK ratio...

Here are some url's to where I have addressed the subject of Morning Glories and nutrients previously...

http://forums.gardenweb.com/forums/load/vines/msg0815113416623.html?3
http://forums.gardenweb.com/forums/load/vines/msg0713394217613.html?3
http://forums.gardenweb.com/forums/load/vines/msg0718450327887.html?1
http://www.google.com/search?q=nutrients+%22Ron_Convolvulaceae%22&num=100&hl=en&lr=lang_en&as_qdr=all&filter=0

Hope the information will be helpful to you...

Regards,

Ron

Here is a link that might be useful: Morning Glories,fertlizers myths and optimal nutrition

Ron, thanks a lot--really appreciate the info. Most sources say MGs grow anywhere, and don't talk about specific needs you may have. You've given me some definite ideas I can apply.

Thanks,
Paul

Paul, I grew the most outstanding MGs in New Mexico at 6000 feet elevation and very poor, hard soil. Even still, you might want to add some compost. I highly recommend a half-inch top layer to all of your flowers every year.

What is 'poor soil'...(?)...This is something that may 'seem obvious' to many people but appearences in this case can often be deceptive...

You cannot reliably determine what nutrients are in a soil simply by looking at it...

Mountainous regions are often rich in Macro-nutrient minerals like Phosphorus,Potassium and Secondary nutrients as well as trace minerals,although Nitrogen is often in short supply...

The soil consistency may be hard or pliable but this is often related to the amount of material that would render the soil conditions permeable to air and water,but soil permeability is not necessarily an indication of the ratio of all Macro-nutrients and secondary nutrients...

So,when referring to 'poor soil' is is helpful to indicate what you think the soil is poor (i.e., low) in (?!)...as soil may be rich in any number of nutrients like Phosphorus or other minerals but low in Nitrogen,but although the soil may be relatively low in Nitrogen,if All of the various nutrients are simply ignored when referring to 'poor soil' then the 'poor soil' term becomes tantamount to another fuzzy misleading term just like the often misused term of 'fertilizer'...

I have tried to address the usage of fuzzy non-specific terms and how they can be very misleading in my previous posts,but Old Myth-leading over-generalizations can be stubborn to dispel...

Think about it...(!)

The Morning Glory species that grow wild in the high deserts are adapted to those conditions and definitely manage to scratch out a living,but the same species when ideally attended to by a gardener and provided with optimal nutrition produce plants that are larger with lush well developed foliage and produce more flowers with healthier seeds...

http://davesgarden.com/guides/pf/showimage/216054/

Hope the aspects that I have mentioned will prove to be helpful for those who are interested to consider the different factors...

Best Wishes (!)

Ron

P.S. My Elementary school teachers always emphasized to "Put your Mind in gear before you put your jawbone in motion..."

Generally I have found this to be good advice...

Here is a link that might be useful: Ipomoea cristulata in the PlantFiles...superb speciemens