My Dwarf Red Dragon Weeping Maple - Grows to only 4-6 feet
	This sapling made it through winter grown in a pot.
Red Japanese Maple and budding peony shrubs

Keep in mind when you place your tree into the landscape that morning sun and afternoon shade suits most maples. Wind and hot sun can wipe a small tree out in no time, regardless of the variety.  Leaves will show signs of stress with burning on the tips. Sometimes the roots will become sun baked and the stress will show up in the leaves as if there has been too much sun or wind. Maples are thin-barked and can be sun scalded during the first year or two after transplanting. This injury can set the trees growth back considerably.  Most maple species are naturally under story plants, we've brought them into the open landscape.

Japanese maples prefer to be somewhat snug in a container. If too much soil is allowed to sit around the root ball there is a greater chance of the soil becoming too saturated with water, which can lead to root rot. This seems to be particularly true for smaller maples in containers.

So it is best not to use a container that is too big for your tree. As a general rule, use a container no larger than twice the diameter of the root ball and half again as deep.  Another way to look at this is not to go more than double the volume of the root ball. As the plant becomes larger, planting in wine barrels or other large containers is a great way to use the maple as an accent on your patio, front porch or backyard.

After two or three years in a container, your tree will benefit from a root pruning and fresh soil.  The outer layer of roots can be pruned or cut off with a saw or sharp knife. Those long, tangled roots around the edge of the pot are not necessary for the plant’s growth.  Only the root tips take up water and nutrients.  If you are returning the plant to the same pot, remove enough root ends so you can incorporate some soil around the perimeter.  There is no need to disturb the center of the root ball.

Start to add a good layer of soil to the pot forming a slight well in the center, as acers prefer their roots to be quite shallow. 

Use the largest pot you can find, at least 5 gallon size (or 14-inches and larger) and make sure there are holes for drainage. Put your container into position in the garden, as it will be too heavy to move once the tree is planted. 

If the compost feels dry to the touch immerse the plastic pot in a bucket of water to ensure your new tree is refreshed before planting. Gently ease it out of the pot and loosen the roots so they're not compressed. 

Position the tree in the well. Fill in the gaps around the roots with soil, pressing down as you go. Make sure the surface is level and the tree is well anchored. The smoothed surface of the soil should be a few inches below the top of the pot. This means that the soil won’t flood out when you water it.

Water the tree well, then keep it watered during any dry spells for the first year until it’s fully established. Your tree will need repotting into a slightly bigger container every few years. Do this in April.

The best time to plant dwarf Japanese Maples or any trees in pots is in early spring or autumn. This is because the weather is still cool, so it won't dry out but also because the ground isn't too hard from the frosts. I prefer to plant them outdoors in pots in spring. Plants in pots are way different than plants in the ground. In a much smaller space, I think they'll get too cold too fast when frost arrives. I want them to have a head start with strong root systems before being left on their own outdoors all winter. I won't be bringing them inside.

All of my Japanese Maples make it through our zone 6 winters without a whimper, and come spring, they're growing buds in March, and leaves in April. I don't wrap or cover them. They stay in their pots with the layer of mulch that they always have to protect their roots. It is advised to wrap them for winter protection, but I have had no harm to my trees by not wrapping them. If I know we'll have awful weather coming, I use frost protection bags over the trees. They have a drawstring at the bottom. Just put the bag on them and secure the drawstring. Watering your plants before ice and snowstorms works for me, as well. Water is an insulator and gives off heat, and it can protect your plant's roots from freezing. To protect the leaves, use the bags.

These maples are happy in all soils, even chalky ones. Heavy clay can be a problem as they dislike waterlogged roots, so be sure to incorporate some organic matter into the hole at planting time. And don’t overdo the watering. 

They’re fairly easy to grow. A sheltered spot out of strong wind is best. Potting your tree into a container twice as big as the pot it is supplied in will give the roots ample room to spread out. Dwarf varieties will thrive in pots and are perfect for small outdoor spaces, like terraces, patios, decks, courtyards, and balconies. As long as you keep it in a spot out of cold winds, they will grow happily in pots for many years. Re-pot every couple of years to help keep them healthy.

You can choose upright varieties or more sprawling, weeping-shaped branches. Go for taller varieties if you're looking to add some height to your garden. If you have an upright tree that's you want to dwarf, pruning and shaping each year, as you would a bonsai (without pruning roots), you can have just about any height bareroot plant and prune to keep it short and the shape you like. For example, if you purchased a tree that grows to 10 feet, and you want to keep it at less than 8, it's easy enough. They grow fairly slowly, so there's not a lot of maintenance.

Water during droughts while the tree establishes itself. Since living in a pot keeps the tree's roots from seeking and finding nutrients in the ground, feed in early spring when the buds and leaves appear, and every 2 weeks until the end of August. Then stop fertilizing until spring. You don't want the tree to grow teeny leaves or new growth that will be frozen off with your first frost. I use 2 organic fertilizers that my trees love. I alternate epsom salts diluted with water or scattered in the pots, and I use Fish Emulsion diluted at the roots, or applied to the foliage. 

I've had spectacular results with these fertilizers on all of my plants and trees. You can read about it here.

Mulching

Mulch is a good friend of your maple. Mulch protects the roots from the heat in summer, the cold in winter and reduces the frequency of watering. Apply a loose mulch, such as wood chips or pine needles over the planted area to a depth of 4 to 6 inches. Be sure to keep mulch several inches away from the trunk of the tree. I "mulch" most of my potted trees with "spillers" and groundcovers.

Fertilizing

Most maples do not require any fertilizer. Once the maple has established a strong root system it will begin putting on top growth.  This sometimes takes one to two years.

Never put fertilizers such as dry pellets or fertilizer spikes containing nitrogen, when planting a maple in the back fill because root injury may result. Be careful with top dressed granular fertilizers which can sometimes release too much fertilizer at a time and thus cause damage to your tree.

Fall and winter are a common time to prune and shape most deciduous trees and shrubs – exceptions to this are maples because they will bleed or ooze sap.   When maples are pruned in late winter or early spring the wounds may flow with sap. If heavy sap flow occurs, pruning should be delayed until it stops or wait until midsummer. This flow of sap can lead to disease invasion and weakening of the tree. 

The trees should not be pruned is during early spring when buds are breaking during leaf expansion or in late autumn because the wound won’t have enough time to heal before winter conditions of freezing or dampness. Maples should be given a thorough pruning every three years and minor “touch up” pruning annually.   A thorough pruning involves removing dead limbs, crossing branches (or branches that will cross in the future). A certain number of branch tips will have died back and these tips can be snapped off with your fingers, or larger branches cut with a pruning tool.

Remove any shoots growing from the base of the plant whose leaves look different from the rest of the plant.  Maples are grafted onto an understock that in most cases will be more vigorous than the grafted scion.  If left to grow, this shoot will take over and out compete the main tree.

Give newly-planted trees and shrubs only minimal pruning. Removing too much top affects the production of food energy (carbohydrates) and can result in poor root development. After planting, prune out broken branches. With young trees, leave some of the lower limbs and sprouts even though they will be removed later. These limbs provide the closest source of food energy for root development.

More Cold Hardy Japanese Maples For My Northern Friends.... 
These are hardy at least to Zone 6.
Many are dwarf enough enough to spend years in pots, and are easy to keep short with pruning.. 

* = trees i grow

*Dwarf Red Dragon Weeping Maple - Grows to only 4-6 feet. My best and favorite dwarf so far. Zones 5-8. 
Red Dragon' is a compact, slow-growing, dissected form that typically matures over time in an upright-pendulous mound to 4-6' tall.  Leaves emerge bright cherry red in spring, mature to burgundy red in summer before finally changing to crimson red in fall. Leaves retain good color throughout the growing season. Purple leaf stalks. Dissected leaves resemble the claws of a dragon. This graceful, small tree creates a focal point or accent for lightly shaded gardens, and is ideal for containers. It drapes beautifully in a decorative pot.

*Orangeola Weeping Laceleaf Japanese Maple- Zones 5-9. Outstanding laceleaf. Orangeola is known for its bright spring foliage and its delicately cascading branches. The leaves have a somewhat glossy appearance. The orange leaves turn to red-green as summer approaches. Weeks later, a new flush of orange leaves arrive and continue throughout the summer. As the fall season arrives, Orangeola's leaves turn dark red before turning a beautiful orange-red. Orangeola performs well in the sun, especially compared to other laceleaf cultivars. Orangeola is a vigorous grower, yet is one of the smaller laceleaf dissectums at 6-10 feet.

Waterfall – A short tree at 6 to 8 feet, this Japanese maple gets its name from the domed, cascading shape of its branches. Its delicate leaves are green through spring and summer but turn stunning shades of red and yellow in the fall.

*Mikawa Yatsubusa – A dwarf tree that reaches only 3 to 4 feet in height. Its large, layered leaves stay green through spring and summer then change to purple and red in the fall.

*Inaba-shidare – Reaching 6 to 8 feet  tall and usually a little wider, this tree’s delicate leaves are deep red in the summer and shocking red in the fall.

Aka Shigitatsu Sawa – 7 to 9 feet tall, this tree’s leaves are a medley of red and green in the summer and bright red in the fall.

Shindeshojo – 10 to 12 feet. this tree’s small leaves go from pink in the spring to green/pink in the summer to bright red in the fall.

Coonara Pygmy – 8 feet  tall, this tree’s leaves emerge pink in spring, fade to green, then burst into orange in the fall.

Hogyoku – 15 feet tall, its green leaves turn bright orange in the fall. It tolerates heat very well.

*Koto-no-ito – 6 to 9 feet, its leaves form three long, thin lobes that emerge slightly red in spring, turn green in summer, then turn bright yellow in the fall.

Winterizing your maple if you live where there are particularly severe winter conditions

Choose sites out of the wind as much as possible.  You can minimize weather problems by picking a good planting site with stable temperatures. Planting near buildings and along inner fence lines helps stabilize temperatures.

Do not fertilize into late summer. Make the last feeding of the season at least two months before you expect the first frost to avoid damage to late new growth. 

Water heavily just prior to freeze. If autumn rains have been insufficient, give your plants a deep soaking to supply water to the entire root system before the ground freezes.  Deep-soaking will help to guard against water loss in winter.

Wrap Japanese maples with burlap (if you experience heavy snows) for at least the first three years. Snow falling in the colder climates can both protect and endanger plants. A good snow cover will insulate the soil similar to a mulch. However snow accumulating on Japanese maple branches will weigh them down, risking breakage. *I mulch the bases, but I haven't needed to wrap the trees (zone 6).

Pruning

A Japanese Maple requires little pruning. It's really a low maintenance tree. Your tree will grow into an eye-catching shape if you let it develop naturally on its own. As autumn comes to an end you might need to give it a quick trim by snipping off any dead twigs. If you feel it's growing too tall or spreading further than you’d like, simply snip back any unwanted growth back to a side branch.

Growing Dwarf Japanese Maples in Pots has become a little hobby for me, sort of a big bonsai, and they're very beautiful and easy to care for. Try It! They can fit into your garden designs just about anywhere.

Additional sources:
This Old House
Gardening Know How

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