@when she felt her wings unfold  
Traditionally, the sun in its splendor does include the face on it but a lot of modern grants of arms keep the term in the blazon while dispensing with the face in the depiction. Usually the sun is just depicted as a gold ball with radiating lines or a rayonné edge.
 
In the Zurich Rolls coat I mentioned, there is a “chief barry wavy argent”. There are thin black lines separating the barry wavy segments without being included in the blazon as them being fimbriated sable.
 
Nope, bleu-celeste is not a metal, but a chief is an ordinary and therefore should be a metal when used above a field of another colour.
 
The problem with the third quarter is that, since it is a chief, it should be described as having three of the plants in it, with the remaining eleven (there’s fourteen, not fifteen plants - my bad) being on the field. Since they are in the third quarter, you could probably get away without specifying numbers like “three, three, three and two”.

@Red Cedar  
Very nice! I was wondering about the overlaid cross and downright ran away from attempting the field. I might refine it to:
 
Quarterly; in the first bleu-celeste on the sun radiated or; in the second bleu-celeste on a mount vert in base; in the third barry wavy of five tenné only the bars fimbriated sable, a chief wavy bleu-celeste, issuant from each mount five beet leaves proper; in the fourth vert five heliotropes proper in saltire; over all a fillet cross argent.
 
The sun in her splendour would normally be drawn with a face, so I changed that a bit. “Proper” gets around the rule of tincture, cheaty though it is. Bleu-celeste is totally not a metal okay.
 
I think I prefer the leaves and ridges to be treated as a pattern but if the number of plants needs to be blazoned I think “issuant from the mounts fifteen rooted beet plants proper by threes in pale” would work. Otherwise you’re rattling off “three, three, three…”.

@when she felt her wings unfold  
Heraldry geek challenge accepted!
 
Quarterly; in the first bleu-celeste, the sun in its splendor or; in the second bleu-celeste, a mont vert in base; in the third barry wavy of five tenné, a chief wavy bleu-celeste, issuant from each mont overall fifteen carrot plants vert; in the fourth vert, five sunflowers in saltire or; overall a fillet cross argent.
 
(Quarters 2 and 3 break the rules of heraldry by putting a colour on a colour. The third quarter was the most challenging. Barry wavy of one colour has at least one historical example in the Zurich Roll, but I had to get creative in describing the plants’ positioning, and I made an assumption on what those plants were, insofar as a crop that would be important to ponies.)

_{^{I quite like “fortitūdinem ex terrā” too. “Strength from the earth”.}}
 
/scrawls ROMANES EVNT DOMVS all over the city walls

No, that’s not Latin. If you actually wantyed a gramatically correct pretentious Latin motto, you should have gone with “fortitudo terrae”.
 
Peace out, yo.

Terra, eh?
 
Waits for obvious WH40K refs.

Ponies make the most adorable supporters.
 
Anyone want to try blazoning it correctly?