I understand that Minimum Cold Hardiness Zone is the lowest zone where the plant will survive, based on how cold the area will get.

I don't understand Maximum Recommended Zone. Would that mean if the Min Cold Zone is 6 and the Max Rec Zone is 11, that the plant will work well anywhere within 6-11?

Thank you, Marilyn (Zone 6a - 14850)

Not as many people actually KNOW the max recommended zone as know the minimum cold hardiness of a plant, which is why a lot of people leave that blank, but no, that isn't what it means.
Some plants are cold hardy, but would not grow well in very hot places. Hostas, some dogwood trees, some cooler growing stuff that maxes out in zone 8...anything over that would be pushing its limit of heat tolerance.
I am in 9A. I cannot grow hostas, Gunnera, all our dogwoods around here died off when global warming made it too hot (Because where I live was ALREADY the southernmost reach of their range), some bulbs that will grow well in the north do not grow here.

@Gina1960 has given you good advice. Many fruits and berries will look nice in warmer weather but need a cold snap to make them sweeter or bloom at all. Because you are in Ithaca you will get all the cold weather you need. After the last frost you can plant your summer crop. For you this is about May 30. The NGA has a page of frost dates for Ithaca:
https://garden.org/apps/frost-...

Start conversations at your local nurseries until you receive a consensus about plants and timing.

I'm in zone 8, and there's plenty that I can't grow either... gets too hot here.

Can you imagine that people plant tulips and then dig them up and throw them away after they bloom once?

too hot here.

you should see the puny taters we harvest... not worth the planting...

but... we can plant canna, flowering ginger, turmeric in the garden and let them over-winter...

Yes, I would love to grow a tulip.

Tulips, snowdrops, daffodils, calla lilies, hyacinths….nope. Gingers, bananas, bromeliads, canneds, brugmandias, lots of palms etc…yes

Folk, you're confusing me! I live in zone 8b. It's 105* to 108* all summer long and I am growing tulips. Not any kind of special tulips. Just bulbs I got from Wally World 3 years ago. This picture is from April 14th last spring. Right now the hyacinth in these beds are blooming, the tulips are growing much bigger then last year and should bloom in a week or two and the crocus are just waking up. And there are daffodils growing in my front yard that I have never watered or fertilized even once. Please help me understand why we are in the same zones but with very different results.

But I can't grow a lily or a daylily to save my life! I'm not blaming that on the heat, just my incompetence. But I sure would like to have them growing in my yard. Any suggestions for my hot climate would be appreciated.

I was wondering the same thing. I grew tulips in my zone 9 California garden. Is the deciding factor the number of chill days? The same numbered zones can have dramatically different climates. The low temperatures might last only a couple of weeks in one location and a few months in another.

"Most tulips need at least 12-14 weeks of "cold period" to develop a beautiful flower. This makes it hard to grow tulips in warm/tropical climates, but not impossible. The cold period is normally given by nature when the soil temperature drops below 55 degrees."

From How to Grow Tulips in Warm Climates
https://wickedtulips.com/pages....

Actually, if a plant is recommended for zone 6 minimum temp and zone 11 maximum recommended, then yes, you do[ have it right; that plant ought to thrive in all the zones in between.

SedonaDebbie, for many spring bulbs, summer dry is as important as winter cold. Many plants (not just some bulbs) respond to dual or multiple triggers for seasonal changes. Often, these triggers will work in tandem, so that together, neither needs to be as extreme as either working alone.

You apparently still have a seasonal temperature change that is enough because you have low humidity and summer dry to work in tandem with the seasonal temperature change. The same zone in Florida does not. Similarly, growers in cold zones have enough cold to do the job by itself, even though their summers are not hot and dry.

We do not have the number and duration of cold days here to grow tulips and other flowers like them. And our summers are wet. Many people in Florida say we have a monsoon season. Winters can be sorta dry, or also sorta wet. Usually it rains every time a cool front from the west/northwest comes and runs into the warm air here. It was 85F here today but a cold front is coming through tomorrow and it will rain. Probably our last cold front this year.

Gina1960 said: no, that isn't what it means.

The cold hardiness is EXACTLY just that- cold hardiness- and only that! It deals only with winter severity, and so it's only function is to help you know if a plant might survive through your winter.

If it survives your winter in zone 3, it WILL ALSO SURVIVE the winters in all higher zones, which explains the range- zone 3 to zone 9 (or 11.) It will survive the winter in all those zones.

If it could survive your summer- through heat and possibly drought, you'll need to find other sources for that info. This is an important distinction- while a plant with a hardness rating of zone 3-11 will survive wonderfully in all those zones through every winter, it may succumb to summer heat or dryness in all zones above 8!

USDA said:
The map is based on the average annual extreme minimum winter temperature, displayed as 10-degree F zones and 5-degree F half zones.

FWIW, the chart makes no attempt to account for 'chill hours' needed for some plants to develope fruit or bulbs to flower. In other words, if a plant NEEDS a minimum cold for a span of time- this chart may not help you. The zone chart extreme cold temp. might only be for a day- but it could be that cold for a month- the zone chart can't tell you that difference. Other charts do- and so will your local extension service.

An attempt has been made to formulate a heat index, but it hasn't gained traction since developed in the 1990s by The American Horticultural Society.
https://www.gardeners.com/how-...

Drought tolerance is another factor that has become a rating for plant summer survival, but has no standardization.

The advice to ask a county extension agent is good.

I meant that the heat tolerance was not what it means. The OP asked SPECIFICALLY about the Max Recommended Zone...the heat tolerance zone. They said they understood cold hardiness. Most people don't know the max heat zone, so they don't list it in their posts to the database.

I grow a lot of tropical plants and orchids, and this type of stuff is very important for that. Unlike more Southern climes in FL, I live in North Central where we have a real, albeit short, winter. Knowing the recommended heat tolerance is supremely important in growing a lot of orchids and higher elevation cooler growing Anthuriums and other aroids.

The heat tolerance of some genera is not absolute across species. That is why orchids are divided onto cold growing, cold to cool growing, cool to warm, and warm to hot.

I can easily grow a cold to cool orchid here in winter. But come summer, it will die a very painful death in the heat.

I can easily grow all of the lowland tropical plants year round in the greenhouse, where I can heat it in winter. But its a lot harder to make the cooler growing highland plants happy. They might easily like 48-50F in winter, but come summer, when its 90+F here day in and day out, they will die.

It's the same for many non-tropical plants. No one grows stuff like red hot pokers here, or Japanese magnolias, etc because while they would easily go through winter, they would not go through summer.

So I take the 'maximum zone' recommendation on the NGA site with a grain of salt. If someone actually puts a value in that spot, I would definitely do my own research and look that specific plant up, and see what its heat tolerance REALLY is. There is a reason why some plants are popular in the North, and others popular in the South. Its heat tolerance, more than cold. Because you can always dig up and store, heavily mulch, bring in a pot, or treat as an annual, a plant that is not cold hardy in your zone. But a plant that isn't HEAT tolerant somewhere like Texas, Louisiana and Florida is a waste of $$$

Like perennial poppies... Like perennial delphinium...

Die from our summer heat...

I can grow annual poppies, and annual delphinium (larkspur).

Gina1960 said: I meant that the heat tolerance was not what it means. The OP asked SPECIFICALLY about the Max Recommended Zone...the heat tolerance zone. They said they understood cold hardiness. Most people don't know the max heat zone, so they don't list it in their posts to the database.

Hope I didn't confuse the OP further. Thxs for your clarification.
There is a lot to unpack in this thread... heat indexes, chill hours- especially for beginning gardeners!

I agree. I fond the climate zones actually to be kind of worthless too. Because every year is different. We had a zone 10 winter this year. And we are in 9A. When the climate maps got redrawn this time, we remained in 9A, while Houston TX was moved to 9B. We are at the same latitude. And while they were absolutely decimated by the polar fronts that moved through there in 2021 ands 2022, we were almost untouched here. So how are they 9B, and we aren't?

Last summer, my town broke the record for the most days over 90F, ever. I think we may have only had 2-3 days UNDER 90. We usually think of October as starting to cool down. But the 90's ;asked into November last year.

I think a good rule for everyone to follow is...research the specific plants you are thinking of planting in your garden, or keeping in your greenhouse. I desperately would like to grow some of the very large leaved/large flowered Pleurothallis orchids in my greenhouse. Ones like P. gargantuan. teaguei, P. titan. But I am hesitant.
I grow a miniature, P. grobyi, that I have had out there for 15 years at least. Even though all these orchids are the same genera, Pleurothallis, some are more heat tolerant than others.
P. grobyi will take a minimum of 40F, while it can take max temps of 95F.
The others I mentioned need warmer nights (around 52-55) and max out in heat tolerance around 80F. Since its routinely 85-90F in my greenhouse, the heat might kill them, and since they aren't cheap, its a risk.

Its the same with flowers and trees in the garden. We have always been told that we are too cold for Tabeuia trees here. Yet, there are scattered specimens growing in peoples yards, both pink and yellow, that have been there for decades. Literature says they need a zone 10 climate. So they shouldn't grow here, right? yet, there they are. If you do your own research, you are much more likely to find things you can reliably grow in your yard than if you rely COMPLETELY on published data. I use that as a guide at best

Then there are the microclimates in one's own site.

Gina1960 said: I meant that the heat tolerance was not what it means. The OP asked SPECIFICALLY about the Max Recommended Zone...the heat tolerance zone. They said they understood cold hardiness. Most people don't know the max heat zone, so they don't list it in their posts to the database.

The Max Recommended zone has nothing to do with heat tolerance per se, for what it's worth. There is always some confusion on this subject.

Let me try to clarify:

The Minimum cold hardiness in the database refers to the absolute minimum temperature a plant can tolerate without dying or experiencing significant damage.

The Maximum cold hardiness in the database refers to actual winter cold requirements, eg. plants that won't bear fruit or make flowers if they don't experience a certain amount of cold. It tells you the maximum zone (which again refers only to cold temperatures in winter) in which a plant will thrive or flower or whatever. Tulips and stuff like that.

For what it's worth, a lot of the Max zones listed in the database are not actually right, because some references end at zone 11 (or whatever) which would be the limit in the continental US. But Hawaii goes all the way to zone 13. So take max zones in the database with a grain of salt if you live in a subtropical or tropical climate.

I say this with a bit of twisted experience because I live in zone 11. You might think that is hot, but no, our annual maximum is usually just over 90°F. The zone 11 designation refers (only) to the winter temperature minimum here, above 40°F or so. Well above freezing. But our climate is not hot in any sense of the word really.

Yes, its definitely misleading. I take it all with a grain of salt and just experiment LOL. I am in zone 9A, but I am in a hot zone 9A. We do have the occasional freeze. This past winter, we had only ONE freeze. Yet San Francisco is in zone 10. They may rarely freeze, but, they don't get warm enough overall to grow a lot of tropical plants. Their nightly lows are great, but, their daily highs just are not hot enough. So my zone 9A is actually better for some kinds of plants than their zone 10 would be.
I am a zone pusher. I always have a few extra plants hanging around, and I have no compunction about planting them out in the yard, even if 'they' say that they won't make it, because usually, a few actually DO make it, and make it long term

I think every person you ask might interpret the meaning of the climate min.max and climate zones differently.

Excellent information Everyone! I don't know about the OP but I think I finally get it! Thank you my friends.