The tropics is a term derived from certain latitudes, a navigational term in fact. There are five of these lines of latitude, The Equator being the central one. Closest to the Equator as you move to the poles, we have the Tropic of Cncer in the North, the northern most latitude at which the Sun can still be seen directly overhead at noon, an event that occurs on the Summer Solstice in June. The opposite tropic, to the South of the Equator, is the Tropic of Capricorn. Between the Tropic of Cancer and the Tropic of Capricorn are the Tropics.

The other two important latitudes closest to the poles are the Arctic Circle and the Antarctic Circle. The areas between the Tropic of Cancer and the Arctic Circle and to the South, between the Tropic of Capricorn and the Antarctic Circle, are called subtropical or semitropical or temperate zones.

Most of the United States is Temperate or Subtropical.

Given the source of the term Tropical, we can then deduce that plant and animal species found in the tropics are deemed tropical and are typically 1) less affected by seasonal change and do not go dormant, 2) are more varied and 3) are quicker to experience change, mutation and evolutionary pressures.

Semitropical and Temperate plants are generally 1) subject to going dormant in Winter, 2) less colorful and varied and slower to experience evolutionary change.

The two definitions above are very general however as there is no reason to suppose that 1) plants and animals defined as tropical, can not survive in and do not range into temperate zones, and 2) that some temperate plants and animals are not capable of great color and variety, 3) that all temperate plants and animals must dormate and 4) that all temperate lifeforms are not capable of extraordinary and/or rapid evolutionary change.

I hope that helps.

I like the term ultra-tropical to describe REAl tropicals. That is what does not grow in California. Those plants that will not live with months of 40f degree nights..they barely can stand 50+ nights. Breadfruit,Heliconia's from lowlands,lowland tropical Orchids. Mangroves to Mahogany trees,etc...And NOWHERE in California is there a place that does not have those temps in winter.
"Plain" tropicals are those plants that come from all year warm climates but can take a chilly winter or light frosts. Why they have remnant cold hardiness to temps they may never see in habitat would take more than i can explain-or even know!...so those should only be planted in the warm months for a real chance to survive.

Temperature alone is not what explains tropicality. Mount Kilomanjaro lies within the tropics; yet, atop that mountain, you find plants that though they are not strapped to seasonal change, are evolved to a specific temperature range that goes well below 40 degrees F/4.5C, especially at night. You may find these plants no where else but in the tropics and ... on Mt. Kilomanjaro. There are similar analogs in the Andes Mountains of South America or atop mountains in New Guinea and other tropical jungle clad areas of the globe.

We all know intuitively that temps are cooler with increasing altitude because we have seen snow on mountain tops.

But have you ever asked yourself why?

Look to the Grand Canyon for an analog. In Summer on the Rim, it can be warm at over 5000 ft. when a high pressure system clamps down on the North American Southwest, but as you go down, it gets hotter inside the canyon. Death Valley is one of the hottest places on Earth and lies below sea level in the Sub Tropics and may I point out, in California. Why is it hotter, the lower you go and/or the closer you get to the Equator?

The answer has a lot to do both with air pressure, but also solar excitation of atoms and molecules. The gravitational mass of a column of air makes the air denser at the bottom of the column and so, there are more densely packed free atoms and molecules that are forced into contact each other, exchanging energy through electron transfers, photon emissions and so forth. This creates increased heat energy.

At the Equator, the column of air is not only thicker than at the poles, where the atmosphere thins, but seasonally, the sun shines more directly on the Earth's surface there as well. The Equatorial air column is thicker due to inertial forces caused by the Earth's rotation. The Earth is not perfectly round, but oblate, both because of inertial bulging at the Equator and because of the distribution of mountain masses. However, rotational inertial forces cause the air column to be thicker there. Due to the thicker air column, equatorial and tropical latitudes are warmer or hotter than temperate and arctic/anarctic zones. But again, keep in mind, temperatures are warmer in the tropics for two reasons, both the increased air column thickness and because the Sun shines more directly upon the tropics.

The differential heating due to air density variance with altitude nonetheless, creates tropical zones that do not necessarily have what we would think are tropical temperatures and tropical plants that surprisingly are not what we might think qualifies as a tropical plant based on temperature alone.

High altitude desert succulants and other plants, thus, though tropical, would die in a rain forest with what we would think of as tropical temps. Yet 32F,0C is a tropical temperature in some places, even right on the Equator.

The one thing that is true about the temperate zones and the Arctic/Antarctic regions is seasonality. The tropics do not see the same seasonal variance that are seen in other latitudinal zones. Therefore, tropicals do not go through seasonal triggered changes such as dormant periods. Nor are their seed's germinations triggered by temperature changes from cooler to warmer, requiring so-called Winter sowing. But be aware, nature has hidden secrets ... plants in what are currently tropical latitudes may have at one time evolved in temperate zones, due to movements of the Earth's crust and shifting of the Earth's rotational axis over huge durations of time. Thus many tropical plants retain vestigial propensities to have seeds that germinate due to temperature triggers and may shed leaves in an annual cycle that does not make sense for tropical plants.

It's a mixed bag due to long term factors and migration of species over time.

Nothing is cut and dry simple.

"Hidden Secrets" "Mixed bag"..very true. Another real factor is that many tropicals can put up with very cold temps for very short durations and die at warmer temps over a longer period. You know what a perfect example is? Pothos.That plain ordinary house plant that grows nowhere in California outdoors-not even the claimed zone 11's. But it does grow in central and into northern Florida( where it climbs with large leafs into the Oaks) and where they have far fewer exotic "tropicals" than coastal California. That's a strange one. Heliconia's that rot in San Diego will return from the roots in upper Florida.
For bay areans,Californians,i have found that night temps might be the "tropical factor"..if they dont grow or can't take cool nights-they wont grow here.Even soucal only has a few months a year of above 60+ year night temps or more...not enough for ultra tropicals.

Humidity and rainfall must be put into the mix as well. CA's summer dryness will be the demise of many tropicals, A good example would be a tropical such as Tacca (Bat Plant) that grows fine in Fla's zone 9 which provides the high humidity it needs.
On the other side of the coin, our low winter temps along with wet weather will cause rotting in many tropicals which tend to go into a somewhat dormant state during cooler weather. Many tropicals will survive our winters with protection from an overhang or cover if they are kept dry.

As pointed out in Bearstate's post, the Tropics have many microclimates. In researching which tropicals may survive depends upon knowing where they come from...not just the country, but the conditions, rainfall and locale where they thrive.

A simpler answer to your dilemma about planting and fertilizing times for so-called tropicals refers to not encouraging fresh tender new growth late in the season that would be more subject to freeze damage. Tropicals in this sense refers to any plant that is not winter hardy in our climate, and would best be planted at the beginning of the warm season to get as established as possible. You avoid fertilizing these plants late in summer so that they foliage has a chance to harden off and not be in active new growth which will freeze more easily.

Many common annuals are actually perennials in the tropics, and might even be used as tender perennials here in California where the winters are warm enough, so annuals can also be tropical plants, but not all of them come from the tropics.

Any plant that comes from the tropics is actually a tropical plant, but not all tropical plants require tropical year round conditions, as other posters have explained above. High elevation cloud forest tropical plants are often particularly suited to coastal California growing conditions, especially in fog belt areas. These plants lend themselves to tolerating subtropical or our mediterranean climate conditions as they will take some winter chilling, yet prefer it to stay above freezing, as our coastal winters mostly do. Tibouchina, Brugmansia, Cannas, Iochromas, etc are all good examples of such plants that have proven widely adaptable to California conditions, as long as they get irrigation during the summer, as all come from places that have summer rainfall in habitat. None of these are suggested as good candidates for planting in late fall, although they can be, as they may get nipped by freezes and die back. So they are the exceptions to planting hardier plants, which are always best planted in fall to best establish them with least amount of supplemental watering and heat shock to the small plants.

I hope that helps you understand the basic concept, without being too technical...

wow, i didnt even ask and my head hurts from all this info. Good stuff!

The most widly dispersed plants that are tropical, temperate and Arctic/Antarctic are probably Algaes. Kelp is a particularly visible example and ranges globally across all latitudes, despite the incidence of sunlight and temperature spread.

And this elides to another fact about species range, the mechanisms by which plant species spread ... carried by water, wind or in the digestive tracts of animals, most commonly ... birds, but could also be fish and other vertebrates, possibly even invertebrate species. Small insects have been found on the wind high above the stratosphere and there is no reason to suppose that seeds and spores don't ride high in the atmosphere ... especially after something like a hurricane's passage. The more common means of conveyance these days is the hand of man ... commercial trade for food, feed and ornamentation, to and from virtually anywhere to virtually anywhere, even into zero G space. Pat yourselves on the back folks. Not only can we change the global climate, but we provide the means of redistributing life's genetic diversity ... without even an a thought of the impact we have.

The melting pot of terrestial zones for plant growth is therefore ever subject to change and injection of new species that alter or mutate with time. The diversity of a latitudinal or altitudinal zone therefore, can have very many surprises.

The definition of a tropical then can be very diverse indeed.

I'd like to take one big half certain guess at answering the original poster's intent ... how to fertilize and care for tropicals.

I think we have established that tropicals can be very like a lot of temperate plants, even in some cases, having vestigial tendancies towards dormancy and special temperature triggered germination requirements.

Soil type is a topic that applies not just to tropicals, but to all plants. There are sandy and well drained soils, acidic, alkaloid and saline to state things basically.

What makes a soil sandy? Silicon in the form of quartz crystals, the break down of silica rocks. But sandy soils need not be silica soils. Granitic or other rock soils qualify. And these soils are typically found at high altitudes in granito-dioritic mountain peaks or in oceanic deposits where the sands are from limestone, coral or shell weathering. Sandy soils are good for rapid drainagea and are important to plants that adapt to those types of soils.

Acidic soils are due to decay products and can be found whereever decay products accumulate, forest floors and so forth.

Alkaloid soils are more difficult to explain, because I haven't that good a notion here as to what causes alkaloid soils, except for maybe, the leaching out of acidic soil components and nutrients, leaving alkaloid remnants. These then would be hard soils found in deserts or drought stricken areas.

Saline soils are what you'd find in tidal areas and mangrove swamps. These soils are typical of areas indundated by salt water and can exist not just along the coasts of continents, but out in the middle of the Oceans on eroding limestone islands where decay makes the soils both saline and acidic.

The types of plants that thrive in these soils have adapted to them over long periods of evolution and may be either tropical or temperate.

If someone else out there can further illuminate on soil types starting from my humble guess, please do so. It's a topic that is of importance to myself and I would think ... every gardener.

I forgot 'clays'.

Clays are mineral rich and very adhesive soils that both retain water and act as a barrier to water transfers deeper into soil layers below them.

Rocky soils can be considered part of the classification of sandy soils ... I suppose. And other place rocky or sandy soils can occur is in riparian contexts.

Then too, there are water submerged soils and epiphytic soils, soils that are actually accumulated by the plants themselves ... so called 'air plants' and carnivorous plants, fly traps and pitchers, etc.

And if its ok,i would like to repeat my definition of a tropical ,semi tropical climate.I think it's one of the better around. My yardstick is....ta da-what is the temperature of your pond(unheated) swimming pool in Jan?. That is for all the boasting of mild climate,water temperatures dont lie. If your in the 30-50f range.temperate.50-60 range mild temperate.65-75 semi tropical..over that,tropical. Give or take a degree. I was reminded of this when on a recent episode of 'Desert Speaks' tv show i saw swordtail fish in a creek in central Baja California.Those are fish famous for actually prefering SEMI tropics.Waters never over the low 70's.Warmer or cooler water being lethal over time.
Just thought i would toss that in..