With shmitta now upon us, there is still a lot of confusion about the different options available during the shmitta year for buying fruits and vegetables. I found the following article online, on the Kosharot website, written by Rav Moshe Katz, and decided to translate it (and add a few words for clarity in the translation - any mistakes are mine). This article is very clear in its layout and explanation of the various option for keeping what he calls "shmitta laMehadrin".

NOTE: I am not writing this here for psak. Any psak mentioned is from Rav Katz and Kosharot. Feel free to disagree or follow your own rabbi. My purpose here is not to publicize a specific psak, but for the clarity of his explanation of the possibilities.

Shmitta LaMehadrin?
[...]
To begin, one must stress that today shmitta is rabbinic in nature and unfortunately we do not merit today to receive the blessings in full that are written in the Torah, that the 6th year will produce enough produce to last for three years. Therefore, we need to find other solutions to the question what we will eat during the shmitta year.

There are 7 possibilities before us:
1. (Isum Shishis) stored from the 6th year - these are produce that gree before the shmitta year began
2. Otzar Beis Din - produce that grew with kedusha of the shmitta year in a way that was permitted via messengers of beis din
3. grown in hothouses, detached from the ground (matza menutak) - shmitta laws do not apply
4. produce grown in the southern Arava region - the area of the southern arava is outside of the halachic broders of Eretz Yisrael for shmitta purposes and thus the produce grown there does not obtain kedusha of shmitta.
5. imported from abroad - imported, not from Israel, thus shmitta does not apply
6. hetter mechira - produce grown, bhetter, during the shmitta year on land that was sold to a non-Jew
7. non-Jewish produce - produce grown in Eretz Yisrael during the shmitta year via non-Jews

each method has its benefits and detriments, we will review them all briefly.
1. 6th year storage - a wonderful solution closest to the solution given by the Torah. The problem is that there is not enough to supply the entire country with produce, especially as there are not many fruits and vegetables that can be stored for long periods of time

2. Otzar Beis Din - it seems, this method is good and worthy, but there are poskim who hold that Chazal did not intend at all for such a form of a business transaction (which includes working the land via a messenger of beis din), but they allowed an organized distribution of the hefker fruits that remained in the field after everyone who wanted to already finished taking. Another problem is with 7th year vegetables, as according to the Rambam these vegetables remain prohibited under the category of sfichin. One using this will rely on the opinion of the "Rash" who allows these vegetables to be eaten.

3. hothouses, detached from the ground - an excellent solution, but from a halachic perspective one is obligated to grow such produce only in a hothouse. This significantly limits the types of vegetables that can be grown using this method (especially as there are poskim who hold that a hothouse is not considered a roof and one would need an actual walled structure). As well, this solution does not provide a solution for all the types of field produce (e.g. potatoes, carrots, onion, etc)

4. southern arava - according to many poskim these areas were not captured by the Jews who came up from Egypt, and therefore for shmitta their status is like the Diaspora and one can grow fruits and vegetables as normal. There are poskim who argue about this, so it is not a complete solution according to all opinions.

5. imported produce - this method has no problems at all of shmitta. The biggest problem of it is that it hurts local Israeli agriculture, which as we have said has yet to merit the abundance of the blessing promised by the Torah and can not yet be an alternative to imported produce.

6. hetter mechira - as its name implies, so it is - a hetter and not preferred from a halachic perspective. The poskim who created the hetter mechira, 2 shmitta cycles prior to Rav Kook arriving in Eretz Yisrael who based his hetter on those who allowed it before him, saw this as a temporary solution based on the economic situation in prior years, and it was deemed a dangerous situation of pikuach nefesh for the people of the new settlement. There is no doubt that today the situation is different, with agriculture in Israel being a small percentage. Still, even during this shmitta year the chief rabbis have paskened to use the hetter mechira.

7. non-Jewish produce - this is produce from Arabs living in Eretz Yisrael. It seems to be an excellent solution, as the prohibitions of shmitta do not apply to them and they can grow produce and sell it to us. However, this causes serious harm to Jewish farmers who need for their parnassa to use the hetter mechira, along with serious ramifications of strengthening the strong grip on our land, whether by Israeli Arabs or by Arabs from Judea, Samaria and gaza, Also, this method goes against the halachic preference of buying from Jews as a fulfillment of the commandment of "Your brother should live with you".  

To summarize, these issues have broad and deep debates and discussions. We have been brief here presenting these topics. In practice, according to Rav Elyakim Levanon, the president of Kosharot, all options presented here are allowed from a halachic perspective. The order of preference brought at the beginning of the article is the order of preference from a halachic perspective.

I thought this was a very good, brief, review of the topics and options for fruits and vegetables. Again, for practical purposes, consult with your own rav, or learn the topics more thoroughly yourself,  about each and any of the solutions you might want to consider eating and require an actual psak about. Rav Katz was very brief and there are many more details and arguments about each and every one of the topics discussed.

The one thing I dont get is that he calls this "shmitta lamehadrin". If he includes every possible option of shmitta produce under the title of mehadrin, what does he consider regular, non-mehadrin, shmitta solutions?