Small-space gardening is popular in places with little to no yard, such as urban areas and office complexes. It may surprise some that flowering trees can be kept in containers or planters. Just like trees in the ground, they need adequate light, air, water, nutrients and drainage (make sure the planter has holes in the bottom). Careful selection of your tree and an adequate-sized container can give you years of enjoyment.
Types of Flowering Trees
Not just any flowering tree will do well in a planter or contained space. Smaller trees (and their corresponding smaller root zones) are the best choice for planters. Many flowering fruit trees have dwarf cultivars, such as oranges, apples, lemons, plums, pomegranates and cherries. Other flowering trees that are naturally small or have dwarf cultivars are crapemyrtles, star magnolias, flowering dogwood, kousa dogwood, fringe tree and vitex (or chaste tree).
Keep in mind that the root zone of the tree usually matches or exceeds the canopy. So if your small tree is meant to get 12 feet wide, the roots are going to try to go out at least that far. This doesn't mean the container needs to be 12 feet wide, but it does mean that every increment less than that will restrict the water availability, nutrients and cold protection that the tree roots are looking for.
Types of Planters
In-ground planters, which are used frequently in public landscaping projects, offer the best protection from weather extremes because of the insulation from the surrounding ground. Large, sturdy containers also work well, but can be expensive for the size needed to hold the root ball of a flowering tree. Box planters can be crafted above the ground with no bottom (functioning as a raised bed for better drainage and soil quality), or just crafted to fit the size of the anticipated root ball. If a planter is constructed against a wall, the wall must have a layer of root barrier and waterproof lining to prevent structural damage.
The fact that planters restrict the root area and the soil available for water and nutrients means that they will require more than trees grown in the ground. Check the planter between rains for dry soil, and water as necessary. Adding layers of compost and regular doses of compost tea or organic fertilizer will help provide nutrients that the tree might be lacking in its small space. Avoid overfertilizing with chemical fertilizers, since this will only encourage the tree to outgrow the limits of the container, placing additional stress on the tree later.
If you're going to be moving the tree around a lot (i.e., moving tropical trees indoors for the winter), put your planter on casters. Set the planter in an area that has a relatively flat path to the entrance of the building. Try to position above-ground containers in the shade of other plants or structures, while leaving the top of the tree in adequate sun. This lowers the risk of frying the roots. Areas sheltered from wind will help prevent rapid water loss through transpiration.