I can't read what was said at that link (maybe it's been taken down) but from what I've gathered from this thread:
"Es sind" often refers to a temporary presence of an object somewhere (which this sentence does seem to indicate - "wow! there are plants in the garden! they won't be there for long, probably!"), whereas "es gibt" is a more permanent presence (and far more widely used) ("there is a garden in the backyard," maybe?), but that's not always the case.
Seems like sometimes "es sind" is describing the state of something, "es gibt" is describing the location.
Guess it's one of these little nuances of the language we'll just have to learn along the way.
I don't know why the link doesn't work for you, it is still active for me. It links to a Google book preview for "Dictionary of German Synonyms" by R. B. Farell. The main comment they have on it is "...es gibt is used in generalization and es ist (sind) refers to the individual and requires to be followed in the predicate by a statement denoting place is not adequate." Followed by (summing up here) that es gibt means that a thing/person exists in a natural way.
So, given what my link says, and what your link says, I think we found it.
The plants in the garden sentence doesn't help me much to remember which is which, so I've been using "Es gibt kein Bier auf Hawaii". A German Schlager song about a guy who isn't married yet because his fiancée wants to go to Hawaii for their honeymoon. He heard that Hawaii doesn't have any beer (so why would anyone want to go there? You can't cool down from doing the hula-hula alone...), so they still aren't married because he's not going to Hawaii since they have no beer.
Original version (to my knowledge): http://www.youtube.com/watch?v=EL-nTBiwdiE
Tom Angelripper version: http://www.youtube.com/watch?v=cLoTkwKgtXE
I am really confused about singular vs. plural here. Why is it "Es gibt Pflanzen im Garten" but not "Es ist Pflanzen im Garten". If we chose gibt instead of geben because of es, then why would the same logic fail with ist vs sind? Conversely, if the plural form sind is forced by Pflanzen, then why wouldn't it be "Es geben Pflanzen im Garten"?
The "es" in "es gibt" is singular, like in "es regnet" (it is raining). It is not referring to the plants, it is more like a fixed part of a phrase. The plants are accusative object here. However, in "es sind Pflanzen" the plants are nominative, the "es" is plural because plants are nominative case. "Es = Pflanzen" has to have congruent case and number.
Addition to bduderstadt's response:
My friend once told me that you could think of Es sind Pflanzen hier as a modification of Pflanzen sind hier, you just put "es" there as a placeholder since the verb has to be at the second position, and you don't want to put Pflanzen there for some reason :) It's not quite true, since the meaning is a bit different, but it helps understand why it's not Es ist Pflanzen hier or not Sie sind Pflanzen hier for that matter.
(Back)yard only means garden in America. In the UK it normally means a small place behind a flat, usually just to keep the bins in or suchlike. Paved or concreted. The only plants will be in pots. A garden has living things growing out of the ground. Now that I think about it I have no idea if Australians use Yard as a synonym for Garden as well. If anyone knows, please let me know.
El encuentro será en mi casa que está en la calle. So no, it's not about perm v temp.
Yes, the "f" has to be pronounced. In many parts of Northern Germany, however, the initial "p" becomes silent, so words like "Pflanzen, Pferd, Pfanne" may sound like "Flanzen, Ferd, Fanne" there. https://en.wikipedia.org/wiki/Voiceless_labiodental_affricate
Depends on context. If "es" refers to something mentioned in a sentence before this one, it could really mean 'they are' or 'it is'. For example "Gärtner kennen ein sicheres Mittel gegen schlechte Laune. Es sind Pflanzen im Garten." "Gardeners know a remedy against bad mood. It is plants in the garden"
However, just by itself, it can only mean 'there are'. "Sag mir, was ist im Garten? -- "Es sind Pflanzen im Garten." "Tell me, what is there in the garden?" -- "There are plants in the garden."
'in' is a two-way preposition. When movement takes place, accusative follows. When there is no movement, dative follows.
Ich gehe ins Kino. Movement, accusative.
Es ist im Ofen. No movement, dative.
I think it is like in spanish, we use Hay = "Es gibt" , to indicate the existence of something (there is/are). But we also use Eso son = "Es sind" literally in english would be like "it are" to affirm or remark what it is in that place.
Not just the existence of something, but what it is, in this case, flowers or "Pflanzen" in the garden