As Dave61 rightly notes, pretty much all cactus fruit are technically edible, but most range from bland to tasteless to unpleasant. Nevertheless there are a large number of cactus fruits that range from passably good to utterly delicious. Most will be at their best when just fully ripe, and often ferment or dry out soon afterward, so strike while the iron is hot. Perhaps the most commonly grown cacti with edible fruits are some of the Mammillarias. These fruits are often quite small, though in a few they can be the size of a nice plump raisin. One of the most commonly available species with tasty fruits is Mammillaria prolifera. Like the much larger but harder to find and to grow, fruits of some species of Echinocactus, the fruits of M. prolifera have a strawberry flavor. They are ready when they turn red, and once they start to shrivel may be past their prime. One wellgrown plant may yield scores of fruits in a summer.

As to pollination, the majority of cacti are what are called "obligate outcrossers", that is, a clone cannot fertilize itself but must be crossed with a genetically different clone of the same species. Of course, in a house there would be no pollinators anyhow (though one might try hand pollination); and for fruit production, it is likely that if you have more than one plant of a similar sort, even if not the same species, they may still be crossable, at least to produce fruit. So if you have a Mammillaria crinita and a Mammillaria prolifera in bloom together (or a gracilis, or whathaveyou) and you want fruit, try using a small brush or Q-tip to transfer pollen from one plant onto the stigmas of the flowers in another... choosing the stronger plant to receive the pollen.

Here in Florida we have a number of large cereoid cacti that grow in yards, the most common being Cereus repandus (syn Cereus peruvianus), whose large red fruits are quite tasty (the red rind is tough but the white pulp, laced with tiny black seeds, is excellent). And many of the local prickly pears, too, have nice fruits. (The Santa Rita and some other ornamental ones, alas, have dry or leathery fruits not very good for consumption.)

Bon appetit!
John in St Petersburg

I have only seen an Epiphyllum fruit once, last summer when i worked for a campgrounds as a grounds keeper. I learned encyclopedias worth of junk about random plants. But i know that these fruits are edible.

I am now actually growing one of these cacti myself. I've only had it for a year, and I'm still trying to figure out what it likes. Have any tips for me?

I just can't wait for it to bloom. Its flowers are just immaculate.

Good luck with yours!
Sandely<3