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Sep 8, 2017 9:58 AM CST
Thread OP
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Xeriscape Container Gardener Hummingbirder Native Plants and Wildflowers
Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator Garden Ideas: Level 2
What does the max zone mean in the plant database?

More specifically, by way of example, what would make a (max 10b) plant refractory to hardiness zone 11, but not zone 10b?

https://garden.org/plants/sear...

I understand some plants might need actual cold in winter to flower or bear fruit, but what plant would survive 40°F winters but not survive 45°F winters? I am having a hard time making any sense of max zones in this context. I would appreciate any feedback. Thank You!
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Sep 8, 2017 10:00 AM CST
Name: Karen
New Mexico (Zone 8a)
Region: New Mexico Region: Arizona Region: Ukraine Cactus and Succulents Plant Identifier Plays in the sandbox
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I've wondered the same thing, Baja.
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Sep 8, 2017 10:05 AM CST
Garden.org Admin
Name: Dave Whitinger
Southlake, Texas (Zone 8a)
Region: Texas Seed Starter Vegetable Grower Tomato Heads Vermiculture Garden Research Contributor
Million Pollinator Garden Challenge Charter ATP Member I was one of the first 300 contributors to the plant database! Garden Ideas: Master Level Region: Ukraine Garden Sages
My understanding is that plant sellers for decades have used hardiness zones to also show how far south their plants can be grown. Lilacs do not grow well in the south, so sellers have historically said they are available down to Zone 7 or 8.

Without a universal "heat zone" available, the USDA zones are used instead.

That's my best guess, anyway.
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Sep 8, 2017 10:16 AM CST
Thread OP
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Xeriscape Container Gardener Hummingbirder Native Plants and Wildflowers
Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator Garden Ideas: Level 2
The hardiness zone is not a great substitute for a "heat zone"... especially on the upper end of the scale.

For example take our climate. We are zone 11 here (winter minimum 45°F). But our summer maximum is about 90°F which would put it below most of the US, I'm guessing. This is not a hot climate, despite the hardiness zone. Those two things do not necessarily go hand in hand.

Supposedly all the plants on the list I linked earlier would not survive here. I would seriously doubt that, not knowing anything about them specifically.
Last edited by Baja_Costero Sep 8, 2017 10:17 AM Icon for preview
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Sep 8, 2017 10:24 AM CST
Garden.org Admin
Name: Dave Whitinger
Southlake, Texas (Zone 8a)
Region: Texas Seed Starter Vegetable Grower Tomato Heads Vermiculture Garden Research Contributor
Million Pollinator Garden Challenge Charter ATP Member I was one of the first 300 contributors to the plant database! Garden Ideas: Master Level Region: Ukraine Garden Sages
I agree but I'm not sure what options are available to us given that the industry by and large has adopted this despite its weaknesses.
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Sep 8, 2017 10:56 AM CST
Plants Admin
Name: Zuzu
Northern California (Zone 9a)
Region: Ukraine Charter ATP Member Region: California Cat Lover Roses Clematis
Irises Celebrating Gardening: 2015 Plant Identifier Garden Sages Plant Database Moderator Garden Ideas: Master Level
"Maximum recommended zone" is the right wording for this category. It's not a matter of hardiness. Certain plants will survive in a higher zone, but will not perform properly. Some classes of roses and peonies, for example, need lower winter temperatures to perform well. The Gallica class of roses will survive in zone 9, but they will not produce as many blooms as they would in zones 4-8, and my herbaceous peonies will not bloom in zone 9 unless I pour ice cubes into the flower beds in winter. The addition of heat zones will not make any difference in this case. Gallica roses and herbaceous peonies are not more vulnerable to higher temperatures than other classes of roses or tree peonies. They simply need colder winter temperatures to perform well.

Last edited by zuzu Sep 8, 2017 11:03 AM Icon for preview
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Sep 8, 2017 1:04 PM CST
Thread OP
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Xeriscape Container Gardener Hummingbirder Native Plants and Wildflowers
Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator Garden Ideas: Level 2
Thank you for that detailed explanation, Zuzu. I understand the use of the max zone category as you have described it.

Can you guess why any of the plants listed as max 10b (link above) would not perform properly in zone 11? I am wondering if maybe some clarification would be helpful when people specify this info. In other words, I question the utility of the max zone category where its meaning is perhaps unclear to the users. For example all these house plants which require near-freezing temperatures in winter (plus a couple dozen more which require freezing temps).

https://garden.org/plants/sear...

The succulents which are listed at max zone 10b (the only plants I would know about) would not be limited above their specified max zone, to the best of my knowledge here in zone 11, except maybe in how they flower, for a few cases anyway. Which is not much of a limitation in the big picture.

I have been seeing little "i" icons on the database edit pages which I can hover over and see a question mark... for example next to Plant Height here.

Thumb of 2017-09-08/Baja_Costero/0812bf

but they are not clickable. (Mac/Safari) Am I supposed to be able to see explanatory text if I click there? Just guessing. Would a similar (but clickable) icon be useful for the Max recommended zone? Something like "Winter temperatures should dip to the minimum temperatures in this zone (or less) for proper plant performance" maybe?
Last edited by Baja_Costero Sep 8, 2017 1:39 PM Icon for preview
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Sep 8, 2017 1:32 PM CST
Plants Admin
Name: Zuzu
Northern California (Zone 9a)
Region: Ukraine Charter ATP Member Region: California Cat Lover Roses Clematis
Irises Celebrating Gardening: 2015 Plant Identifier Garden Sages Plant Database Moderator Garden Ideas: Master Level
Those icons are not clickable, as far as I know, but I'm not using a Mac. When you hover over them, they should offer the explanatory text. As far as your suggested information is concerned, I think it might not be necessary. I think that most of the plants with 10b listed as their maximum recommended zone are on the list in error. Many websites seem not to recognize the existence of zones 11, 12, and 13, and they routinely list zone 10 as the highest. If information for our database is taken from those websites, which tend to list appropriate zones as 5-10, 6-10, etc., it's incorrect information and should be corrected. I think that certainly would apply to the succulents.
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Sep 8, 2017 1:42 PM CST
Garden.org Admin
Name: Dave Whitinger
Southlake, Texas (Zone 8a)
Region: Texas Seed Starter Vegetable Grower Tomato Heads Vermiculture Garden Research Contributor
Million Pollinator Garden Challenge Charter ATP Member I was one of the first 300 contributors to the plant database! Garden Ideas: Master Level Region: Ukraine Garden Sages
The explanation on those "i" icons is simply reminding the user to write "inches" instead of using the quote marks.
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Sep 8, 2017 1:46 PM CST
Thread OP
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Xeriscape Container Gardener Hummingbirder Native Plants and Wildflowers
Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator Garden Ideas: Level 2
The history explains a lot. Thank you Zuzu.

I'm not sure how to correct the legacy entries you mention (the big "bump" of plants at zone 10b) except to remove the max zone listing from most of that group... not knowing what to substitute in its place, perhaps better nothing. Though of course that will incur some information loss.

When I hover over the "i" icon, I see a question mark (only), everywhere it appears on the page. Maybe that's a Mac thing.
Last edited by Baja_Costero Sep 8, 2017 1:46 PM Icon for preview
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Sep 8, 2017 2:15 PM CST
Plants Admin
Name: Zuzu
Northern California (Zone 9a)
Region: Ukraine Charter ATP Member Region: California Cat Lover Roses Clematis
Irises Celebrating Gardening: 2015 Plant Identifier Garden Sages Plant Database Moderator Garden Ideas: Master Level
It would be a good start to remove the 10b maximum zone information from plants that you have seen growing well in your zone, and I think it's best not to enter a substitute in these cases. Just leave the maximum zone field blank for those plants. It's possible that planetary climate change could be adding new zones before long. I may be mistaken, but I think our own database once went up only to zone 11 and didn't include zones 12 and 13 among the maximum zone options.
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Sep 9, 2017 11:28 AM CST
Thread OP
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Xeriscape Container Gardener Hummingbirder Native Plants and Wildflowers
Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator Garden Ideas: Level 2
OK, I'll tweak where I know the plant.

Maybe it would be helpful to make the max zone dropdown items look like the minimum zone dropdown items? Indicating the minimum temperatures in the same detailed way next to each zone.

That would presumably be some sort of virtual copy and paste (I can only imagine) but maybe it would help emphasize that the winter minimum is the thing that matters in this category as well. And it's not necessarily redundant if you haven't already clicked through the min zone part first.
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Sep 14, 2017 10:14 PM CST
Thread OP
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Xeriscape Container Gardener Hummingbirder Native Plants and Wildflowers
Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator Garden Ideas: Level 2
For the curious, there's an interesting (and relevant) article here on "chill hours" and the sharp decline in Georgia peaches, which relates to the importance of winter chill for performance.

https://fivethirtyeight.com/fe...
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