Here are some examples of permaculture guilds we have tried with planting under or next to trees:
 

• We have had reasonable results planting tomatoes under trees. For some reason, the two seem to work well together as long as the tomato plant receives at least 5 hours of full sun, preferably in the morning. Therefore, we have been planting tomatoes on the east or south sides of an oak tree. Production is less than half what it would be in full sun, however, the fruits rarely have any insect damage or suffer cracking or rot. Perhaps this is because the plants are not stressed by the full sun and heat. An added benefit to this is that the tomato does not need to be covered for an early frost since the tree protects it. We have found that our tomatoes can withstand nights down to 30 degrees without damage in this arrangement. In our climate, this can extend the growing season by a couple weeks or more if we have our typical early frost. 

• We have planted peppers and eggplants under a pear tree providing minimal shade. The plants in this location have performed very well, and with the tree in the middle it is easy to cover the plants in fall with a covering to protect them from frost since I can hook the covering on the tree, thus holding it above the plants. If the covering is in contact with the plant, the top leaves are more likely to freeze.

• In spring of 2005 we began an experiment of broccoli surrounding a 30 foot tall wild cherry tree. I had trimmed the lower branches of the tree to about 8 feet above the ground in order to ensure adequate sunlight under the tree. Outside the broccoli we planted a ring of cabbage, and outside the cabbage we planted a large ring of asparagus (at the drip line of the tree). The asparagus had done very well. The broccoli on the south side of the tree produced well, although those on the north side were not nearly as productive.  I had planted most of the broccoli toward the south side of the tree such that it would get adequate sun in the fall. This worked out well because during the summer months when the weather is hot and broccoli bitter, it did not grow much due to the tree blocking most of the sunlight. In the fall when the broccoli sweetened up again, it received plenty of sun from the south since the sunlight came in under the branches, resulting in renewed harvests of florets. Of course, letting it grow all year does not produce the big heads you see in the supermarket, but the florets are just as useful for our cooking purposes. The cabbage performance was mediocre. We harvested a few average heads but there were no large heads like you would find in the full sun. We had a few small heads at fall harvest, however, that grew back after harvesting the initial heads during the summer. This performance is consistent with other cabbage we have planted in partial shade. It appears that cabbage requires maximum sunlight in order to produce large heads. In subsequent years, we planted a slow spreading mint inside the circle of asparagus and it has done very well.

• In 2005 I planted Irish potatoes under, at the drip line, and just beyond the drip line of a 25 foot pecan tree that had some low hanging branches only three feet above the ground. I was very surprised to find the best production to occur at the drip line. Interestingly, the production directly under the tree where the potatoes were heavily shaded was just as good as the production in full sun. I think this was mainly due to the fact that we experienced a springtime drought in 2005 and thus the potatoes at the drip line and under the tree were not stressed by the heat and dryness brought on by the drought. I noticed that the potatoes planted at the drip line and under the tree also lived longer. I think this may be due to reduced leaf hopper damage since leaf hoppers like to do their dirty work in the full sun. I also planted a ring of potatoes around a small plum tree with similarly pleasant results. I harvested almost a full grocery sack of potatoes from that circle which was ~12 feet in circumference. Again, these plants lived longer than they typically do in our climate when planted in full sun.

• We planted sweet potatoes under a plum tree, and although they showed much leaf growth, they did not produce much tuber. I think much of the reason for this is that they were planted too late in the season. In our climate, sweet potatoes require as much growing season as is available along with plenty of heat and sunlight. Although this planting combination would work well in the tropics, it did not work so well in our temperate climate. It also had the disadvantage of requiring lots of digging near the tree roots in order to harvest the potatoes (in contrast to the Irish potatoes that place their tubers on top of the soil if planted in mulch, therefore requiring little or no digging). 

• We have had excellent success with winter (Egyptian) onions around fruit trees. This onion is almost finished with its harvest period when the tree has just leafed out, therefore, this combination works well together (assuming you have a use for winter onions). Furthermore, planting this onion (or any of the allium family) around stone fruit trees tends to repress the peach borer - a major fruit pest in our area.  In fact, any bulb would make a desirable companion for fruit trees - that means flower bulbs too. The growing cycle of tulips, daffodils, etc. is such that their primary leaf growth is nearly complete when fruit trees are just finishing leafing out. This means that the shade of the fruit trees would only minimally affect growth in the next year's flower bulbs. This would be an easy financial additions to an established orchard since the cut flowers it would produce may bring in as much or more income as the fruit, and using this approach, no additional land would be required. Furthermore, you would have the advantage of the bulbs assisting with insect control in the orchard (although the bulbs might attract voles). 

• Purslane is another plant that we have found to grow well in partial shade. Although some farmers might consider this a weed, we have found it to be a nice late season addition to salads and it reseeds itself regularly. 

• Our tropical cannas have performed well under a shade canopy as long as they have adequate moisture. In fact, we found that they perform better in partial shade than in full sun.

• In general, I have found that broad leaf plants will perform acceptably in partial shade conditions (comfrey is another example I have had  success with).

 

It can't hurt to experiment with various combinations. Such plantings also make the landscape more interesting. I have given numerous tours of our yard/garden explaining some of these applications.

 

See our Permaculture Examples page for more planting examples.