Miniature or dwarf fruit trees produce regular-sized fruit on smaller trees. A three to four-foot-high apple tree might produce up to 45 apples of a regular apple variety. A two-foot-high peach tree in a pot can produce 25 to 30 fresh peaches. Miniature trees are popular with people who own backyard and balcony gardeners and want a small amount of several fruit tree varieties.
To choose which type of miniature to grow, you'll need to decide if you want a potted tree, a tree trained by pruning (espalier, cordon, fan), or a "bush" tree with minimal pruning. The type of tree you want to grow will need to be kept miniature by one of the methods outlined below. Not all varieties of fruit are available as dwarf trees and the sizes are restricted by various means. It's a good idea to understand what types of trees fare best in particular growing situations.
Genetic Dwarf Fruit Trees
Some miniature fruit tree varieties are genetic dwarf trees—trees that have DNA that causes them to be very short with fairly heavy branches. These are not regular varieties made smaller, so you may not be able to get your favorite apple or peach variety as a genetic dwarf. Dwarf varieties are most often peaches, nectarines, almonds, apricots, and apples, small enough to grow in pots. The fruit will be normal-sized. Depending on your area, these smaller trees may need winter protection.
Dwarfing Rootstocks for Miniature Fruit Trees
Branches of varieties of regular-sized fruit trees are often grafted onto dwarf rootstocks to produce smaller trees. Several varieties of dwarfing rootstock are available which restrict the tree's growth to various sizes. If you're choosing trees for a backyard orchard, you may want to grow several smaller trees of your favorite varieties, rather than one large tree with a few popular varieties grafted on. These trees will need pruning for fruiting buds, but not as much for size maintenance.
Dwarfing Rootstock Varieties
Dwarfing rootstocks all have their own peculiarities. Some are suitable for particular varieties but are too restrictive for others. Some are resistant to drought and will grow on poor soils, others need high-quality soil to produce fruit. The dwarfing rootstocks produce fruit trees that range from three to four feet high apple trees on M27 rootstock, to six to eight feet high on M9 rootstock. Before you choose to grow the smallest possible trees, you need to understand what type of soil and growing conditions will support the tree in your particular dwarf rootstock.
Very low bush apples are easier to manage on highly dwarfing rootstocks such as M27 and M9. To grow an espalier, a fan, or a cordon, you'll need longer branches and a more vigorous tree. M26 or MM106 are better for these.
Dwarfing rootstocks are not the same across all fruit varieties. Although you can produce three to four-foot-high dwarf apples, a dwarf cherry is still a tree 18 to 20 feet tall. To grow a cherry tree, you can cover with netting to keep the birds from eating the fruit. You can also add netting to a cherry tree that's against a building with the espalier technique.
How to Choose a Dwarfing Rootstock
Choose a dwarfing rootstock based on your soil as well as the size of tree you want. The rootstocks which produce the smallest trees are M27 and M9 for apples, Pixy for plums, and Quince C for pears. They're only suitable for high-quality loam soils with good fertility. Trees grown on these rootstocks have extremely restricted root growth and will need to be staked for their entire lives.
Less dwarfing rootstocks; M26 and MM106 for apples, Colt and Gisela 5 for cherries, and Pixy for peaches, need staking for the first five years of life. After the initial staking period, their roots should be able to support them on their own.
Determining Your Nursery's Rootstocks
All nurseries should be able to tell you what rootstocks are used with their dwarf fruit trees. Some specialist nurseries will graft the varieties you want, on suitable rootstocks for your purpose. If you want a heritage apple or a specialty apple on a rootstock for a cordon or espalier, ask a fruit nursery if they can supply you with a particular variety and rootstock combination best suited for your soil and the type of pruning you want to do.
- Dwarf Rootstocks for Apples: The most common dwarfing rootstocks are the Malling (M) rootstocks, developed at the Malling research station in England, or the Cornell-Geneva (CG) Rootstocks created at the Geneva Research Station in New York. Rated most dwarfing to least dwarfing these rootstocks are available as M27 (three to four-foot trees), M9 (six to eight-foot trees), M26. CG 11 is similar to M26 but has more resistance to some diseases. In some areas, MM106 is also used, depending on the pests it must resist.
- Dwarf Rootstocks for Pears: In order from most to least dwarf, the common dwarfing rootstocks are Quince C, Quince A, or EMH.
- Dwarf Rootstocks for Plums, Damson Plums, Peaches, and Nectarines: Plums, peaches, and nectarines are dwarfed using the rootstocks Pixy or St. Julien A.
- Dwarf Rootstocks for Cherries: Cherries are most often dwarfed on Colt or Gisela 5 rootstocks. On Gisela, five sweet cherries may grow to be 10 to 13 feet on Colt rootstocks sweet cherry height is 20 to 26 feet. Sour (acid or "Pie" cherries) are less vigorous, growing 10 to 12 feet on Colt rootstocks.
- Dwarf Rootstocks for Apricots: Apricots can be dwarfed on St. Julien A or if potted up, Torinel.
Controlled Pruning to Produce Miniature Fruit Trees
Several methods of pruning produce fruit trees of a more manageable size. These trees may be on regular rootstock but are more often on a dwarf rootstock chosen to grow to a particular size. Two of the most common types of controlled pruning are:
- Espaliers: Where the trees are grown flat on a set of wires on a building or between posts.
- Cordons: Where single straight branches are interwoven to create fence patterns.
Any variety on any rootstock can be espaliered or grown as a cordon which makes them useful for decorative fences or for growing flat against the protection of a wall. Cherry trees, often difficult to grow as dwarfs (a dwarf cherry may still be more than 20 feet tall) can be grown shorter if pruned against the wall as an espaliered cherry.
Root and Branch Fruit Tree Pruning in Pots
Pot grown fruit trees, with restricted soil and root growth, can be dwarfed similar to the way a bonsai tree is dwarfed, with careful pruning of the roots and branches at the correct time of year. Like bonsai trees, this can be done with any fruit variety on any rootstock. Many dwarf pot grown varieties are grown on dwarfing rootstocks to further restrict their size. These will require careful watering and feeding according to the rootstock used.
Fruit trees can be grown in large pots (10 to 15 inches), except for cherries, which need larger pots up to 18 inches across. Growing trees in pots will restrict their size even without pruning. Fruit in pots should be grown in fertile soil with one-third of the soil mix being perlite or vermiculite to keep the soil from getting waterlogged.
Fruit trees require good fertility. You can use slow-release fertilizer pellets, or feed them every two weeks with a high potassium liquid feeding (tomato fertilizers or another high potassium liquid). Fruit trees in pots should be repotted every year or two after leaf fall. When your tree has reached its mature size, it should be root pruned every other year and replaced back in its pot with roughly 20 percent new soil. Root pruning for this purpose should remove at least the outer inch of roots. In years when the plant isn't being root pruned, you should mulch the soil well with organic material or add new compost to the top of the pot.