Growing Japanese Morning Glories: Tips for Stunning Late-Summer Blooms

I use the term "Japanese morning glory" loosely to refer to exotic Ipomoea nil cultivars, as opposed to the more common Ipomoea purpurea types. The blooms of Japanese morning glories are usually larger but produced—in my climate at least—in much lower numbers than their common cousins. Fortunately, gardeners tend to have a weakness for challenging plants!

I don't have ideal growing conditions for Japanese morning glories. They prefer sandy soil, but the long utility building where I plant most of mine sits on nearly pure clay. They also appreciate a long growing season. Here in Pennsylvania, I usually have to wait until late May to set them out. Since they tend to stall during the hottest part of summer, by the time they begin blooming well in late August, nights are already cooling. That combination of chilly temperatures and heavy dew on their large buds causes many flowers to tear themselves apart as they try to open, leaving the blooms I do get often ripped and tattered.

I don't have a trellis either, so I improvise with green baler twine, which we have plenty of on the farm. I run one horizontal line near the ground along the length of the building, another about halfway up, then tie vertical strings between them.

I try to keep each morning glory on its own string for seed-saving identification, but they quickly tangle with neighbors. It's probably just as well, since they seldom have time to set seeds here anyway.

So why bother with Japanese morning glories? Simply because few blooms are more beautiful. They also give me something to anticipate in late summer when most other flowers are fading.

Growing Your Own

If you want to grow them, you'll likely need to trade for seeds or purchase them on online auction sites, as few large seed houses carry them. I frequently request specific Japanese morning glory seeds for Christmas gifts—ensuring at least one present I'll love!

Morning glory seeds remain viable for quite some time, so I plant both old and new varieties each year. I select about 20 types from my accumulated seed packets. Using small pudding or yogurt cups labeled with names, I soak two seeds of each type overnight. Then I sow the seeds (which usually have started to crack open) about 1/4 inch deep in six-cell planting packs of seed-sowing mix—three varieties per pack.

They germinate quickly, within a couple days to a week. Sowing two seeds per type usually ensures at least one germinates—though not always! You may need to nick the hard or fuzzy coats on species morning glory seeds before soaking, but Japanese varieties seldom require this.

When transplanting seedlings into a long row on the east-facing wall of the building, I sprinkle leaves with cayenne pepper to deter rabbits and groundhogs. Slug bait around the plants is also wise.

I don't fertilize morning glories, having heard horror stories about excessive foliage and few flowers. You might get away with a bloom-booster fertilizer low in nitrogen—if any of you have tried this, please share your results!

Finally, don't forget a morning walk to admire the blooms. Many close by noon, though they stay open longer once weather cools. The shiver you feel when you spot them won't be entirely from dew-soaked shoes!

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All photos are my own. The thumbnail shows the Japanese morning glory 'Ukigumo'.