The tree had a hand written tag on it with the name 'Zulko' which may have been 'Zuiko'.

山モモ (yamamomo)
�"�種名 (cultivar): 瑞光 (zuikou or zuiko)

�"�酸っぱい実は�"�食�"�、ジャム等に重宝です。
The sweet and sour fruit is prized for eating raw, making jams, etc.
樹勢強く栽培容�"です。
The tree is vigorous and easy to grow.
庭の片すみに、鉢植えに面白い果実です。
Looks interesting fruiting in a garden corner or as a container plant.

育て方のポイント
Planting instructions:

庭植えの場合
In-ground planting
日�"たいが良く水はけの良い所なら土質は選びませ� �"。
Choose location according to ???
植え穴を掘り、腐葉土と土とを良く混ぜて植え込�"� ��水をたつぷりとそえて下さい。
Please dig a hole, mix in humus/compost, soil ???
肥料は春先に1回、夏・秋各1回位、油かす、化学肥� �たそえます。
Fertilize with rapeseed oil cakes, chemical fertilizer (can't figure out the frequency).

鉢植えの場合
Container planting
6〜7号鉢に赤玉土6、腐葉土3、砂1の割合で植え込む� �
Use 6 parts number 6 or 7 Akadama (bonsai potting soil), 3 parts humus/compost, and 1 part sand.
水やりは鉢土の表面が乾いたらそえる程度でよい。
Water when the surface is dry.
肥料は玉肥を3〜4個、毎年春先と夏に鉢の周りに埋� �込む。
Every year, embed 3 to 4 pellets of bonsai fertilizer around the edge of the pot.

※印刷物の為、写真と色、形が多少異なる場合があ� ��ます。
"Actual plant might differ from image on label" kind of thing

Hopefully you can find out more using the cultivar name. I think some sites say that they have distinct male and female plants.

Anyway, the important thing is that the cultivar is Zuiko. They don't list the root stock on the label. From what's on other sites it might be a female plant.

If you scroll down on this page it seems to list different types of yamamomo cultivars. Google translated page puts Zuiko as the 4th on the list and that "[i]n the bayberry, the most popular varieties."

I assumed all of the trees I ordered were female. I had one tree grown from seed when I placed the order so I was hoping it was a male and would pollinate them. Now, all the trees except this 'Zuiko' have died, including the seed grown one. This one is doing fine but I noticed the root stock was sprouting leaves with a jagged edge that looked a bit different than the top growth. I'm thinking I'll just let one branch of the bottom growth get big enough to bloom along with the top.

I know that in China and Japan they don't have to worry about male trees because there are so many wild ones nearby. Here in the states not that many people grow the tree so it will be harder to find.

Thanks for all your help