Here's a rough guide to what fruits are in season now, early summer. I hope it might be useful to you in staying well fed while you are in China.
The list will obviously differ from one part of China to another. Best to ask some local gray-hair/long-beard types who have lived in your new temporary hometown for a long time. Even many younger locals, especially the women, will have been schooled by their mothers and grandmothers and can help you some.
In the market I always ask lots of questions. I ask the old lady who is shopping for same thing I am why she buys this piece of fruit instead of that one. Why the dark ones and not the light ones?; why the ones with leaves attached?; why those big ones with the obvious blemishes? They usually seem to enjoy helping me. I also ask the vendors why one bin costs more than the one next to it. Maybe simply that these are small and those are large. Maybe those others over there are very ripe and need to be used today. Vendor must move them out. Don’t assume or guess; better to ask.
What I did when starting out was to actually follow people who seemed to fit the demographic of “wise locals” in the outdoor wet market/"farmers market" 农贸市场 and copy their buying habits. I also made a note of how much they paid after bargaining, so I didn't have to shell out the "foreigner price." I took lots mobile-phone snapshots; still do. I made a point to learn the name of things. I asked the vendor, I looked for signs. I whipped out my notebook and a pencil and asked someone standing nearby to write it out for me. Then I read up on it when I got home to try and learn a little more. Baidu is great for that. Run it through a translation app if your Chinese isn’t up to the task.
Vendors love to tell you how to cook whatever it is that they sell. 95% of them are eager to help you turn it into a good meal. Share your plans. “I was thinking about frying this with some ham, what do you think?” Some are reserved at first, but once they see your ears are open, realize you aren't arrogant, the good, sound advice pours out. It can be priceless; save you tons of grief.
Don't try to be James Bond about any of this; it is not a covert action. If people gave me a funny look, I just explained I was recently arrived here on these shores and was trying to learn how to shop wisely by studying their methods. Most seemed flattered and some took me under their wing to voluntarily explain all sorts of other stuff I would not have dreamed to ask. Even what bus to take to get home, where to get an honest bowl of noodle soup; good place for a haircut or a foot massage.
One very common buying axiom, that locals apply to most vegetables as well as fruits, was “buy it today, cook it today” 今天买，今天吃。 Especially true for leafy greens, of course. Potatoes, carrots, and big red onions would a keep a couple days longer. Ginger and garlic could be kept on hand. There were other exceptions: lemons, limes and oranges could last several days.
Several fruits are better poached or stewed. Seems counter-intuitive, but it’s true. This is probably the default method to enjoy local peaches and plums, for example. Lots of Chinese people seldom eat them raw. Poaching enhances flavor; boosts the taste. Some fruits are real good steamed, even though that approach is uncommon in the west.
I seldom, almost never, buy fruit and vegetables in the supermarket. Very simple reason: longer supply chain. It may have been picked or harvested a couple weeks ago. The produce I get at the outdoor market was in the ground or on the tree yesterday. At least much of it. Need to seek it out. Learn how to get the good stuff for your own table. One insider's tip: shop in the morning if you possibly can. Vendors often sprinkle water on fruit (and vegetables) all through the day to keep it looking fresh.
You don’t have to be a great sleuth to figure most of this out. If you go to a fruit store 水果店, just look to see what’s featured; what gets most of the counter space. If you go to the outdoor farmers market, see what is piled up left and right. See where locals are lining up and look at what’s in their shopping bags if you meet them on the street.
Anyhow here’s a “from the top of my head” list of what fruit is locally available and in season now in Kunming. Please contribute if you see errors or omissions. Please expand it with info from your part of China.
Remember, where you live the crops might very well be different; Harbin is a long way from Guangzhou.
Apricots, peaches, plums, nectarines. These are the “summer stone fruits.” 杏儿、桃子、梅子、油桃。Good right now. Will be finished in three weeks or so, depending on the weather (mainly how much rain falls.) Here's a recent post about one good way to deal with the peaches:
Smaller, locally grown cherries 樱桃 are in season now (almost at the end.) The great big ones 车厘子 from South America (Chile) arrive in the winter.
Blueberries 蓝莓 are abundant now, but they have a short season. Won't last long. Big ones cost more than little ones.
Mangoes 芒果 are in. Lots of them are from Thailand and Burma. They will get cheaper in a week or two. In three or four weeks, they will have vanished.
Watermelon 西瓜 is abundant and flavorful. I think the small ones are sweeter. Some are trucked in from Burma. 5 or 6 yuan per kilo. Get the seller to cut it up. Doesn't cost any extra. (Ditto for other melons.)
Cantaloupe 哈密瓜 and Honeydew melon 蜜露瓜 are good now. They are just starting. Some are local, some from Xinjiang and Qinghai. The best will be from Xinjiang in two or three weeks.
Grapes 葡萄。Many local, green ones and red ones; seedless and seeded; tender skin and thick skin. Large vineyards near Mile 弥勒县。Some brought in from Xinjiang and Qinghai. Parts of Gansu and Ningxia.
Bananas are still good. They have a long season. Some are from South Yunnan. Some are from Hainan. 5 to 10 Yuan per kilo. The small ones from South Yunnan are excellent. They are called 八角 and have twice the flavor of the big ones. Cost 50% more.
Lemons are cheap and good; limes are expensive and kind of dry. Six weeks ago, the situation was reversed.
Dragonfruit 火龙果 is good now; plentiful and relatively cheap. 10 to 15 Yuan per kilo.
Lychee 荔枝 are great now. About 15 Yuan/kilo. Look for ones that say 妃子笑。It’s a particularly flavorful cultivar. Local ones from South Yunnan, Honghe Prefecture. Many are from Vietnam. Some from Thailand.
Longyan 龙眼 aren’t ready yet, but will be soon. Wait a week or two. Keep your eyes peeled.
Strawberries, raspberries, blackberries are over for the year. So are local (south Yunnan) pineapples. You can still find a few, but they cost twice what they did three weeks ago.
Forget about avocados牛油果。Imported ones don’t ripen well and cost way too much. Local ones are scarce. Chinese don’t much like them. No demand means very limited production.
Grapefruits 西柚/葡萄柚 are arriving to some fruit stands, not all. They aren't local; not sure where they're from. Frankly, I"m not sure about them.
Pomelo 柚子 (much larger than grapefruit) is finished (it’s a winter fruit.) See a few oranges and tangerines, but not many. (More in the cold months.)
Pears get good when the weather turns chilly in the fall of the year, after 中秋节。Apples are at their best in fall and winter too. The big orchards of NE Yunnan are dormant now, for example. (昭通州)
Shanzhu 山竹 (mangosteen) are finished for the year. Best are from Thailand.
Yangmei 杨梅 and rambutan 红毛丹 are finished for the year. (early spring fruit.)