Japanese Maples make great container plants, but there are some differences from planting them in the ground. Initially, small maples should be planted in an ornamental container and not kept in the black plastic pot they are shipped in. The black plastic pot absorbs the sun and can cook the roots. It does not provide insulation for summer or winter. I do not guarantee maples that are left in the black plastic pot they are shipped in. Either keep the plastic pot in the shade, during the summer, or put the black plastic pot inside another container to keep the sun off. Transplant to an ornamental container in the fall or winter. This time of the year helps to prevent transplant shock. Use SuperThrive for all transplanting.
Important Note: Make sure your container is larger at the top than the middle or the bottom. Pumpkin shaped containers look good, but do not allow for easy transplanting or root pruning without mangling the root ball or breaking the container.
The new ornamental container should not be more 4-6” larger than the current pot. This gives the roots 2” or a little more room to fill. Do not put a small root ball into a large container. It cannot absorb all of the water/moisture in the container and will get root rot. When repotting use a loose/inexpensive potting mix that has wood bark in it or buy some to add. Do not buy a potting mix with fertilizer in it. You want a loose potting mix that provides good drainage. To check on the looseness of the potting mix take a handful and close your hand to make a fist – if the potting mix stays in a ball after you have opened your hand then the mix is too rich and more wood chips are needed.
Maples do not like a lot of fertilizer and may lose their variegation if over fertilized. You only need to fertilize maples in containers – they do not need fertilizer when planted in the ground. SuperThrive works better for in-ground maples by stimulating the roots to grow which helps the maple to thrive. For containers, only fertilize once in the spring, with a slow release fertilizer like Osmocote or Apex 14-14-14 (you can go smaller on the Nitrogen level the first number in the sequence). Small maples should live most of their lives in a pot or at least until the maple is about 3’ tall with a nice trunk. The best time to transplant any maple from a container to another container or to put in the ground is in the winter when they are in their dormant period. The dormant period is also the time for root pruning which is another subject I am working on.
During hot summers it is sometimes difficult to keep a smaller pot watered as they tend to dry out more quickly. Once the soil is too dry the water runs right through the container and is not absorbed by the root ball. Every couple of weeks I often water from the bottom the smaller containers by placing the pot in a couple of inches of water in a bucket or tray – whatever you have available. Sometimes I use this opportunity to add SuperThrive to the water in the bucket, but not quite as strong as when I initially plant my maples. The pot should be set in about 1-2” of water – then carefully pour some additional water into the pot and allow the water to run through the pot into the bucket/tray. Leave the maple in the water for 10-15 minutes. To make sure the maple is well watered – use the weight of the pot as a guide. In other words a heavy pot doesn’t need water. Repeating this process once every couple of weeks may be too much water. Use the weight of the pot as your guide. Remember slow growing maples use less water than faster growing ones. You may only need to water a slower growing maple every 7 to 10 days. When the container is light the maple needs water. It is important to water thoroughly by leaving it in the bucket until the roots have absorbed as much water as they can and then allowing the maple to dry out before watering again. Keeping your maple wet all of the time will eventually cause root rot. Statistics show that 99.9% of all maple deaths are caused by over watering and/or poor drainage. Once the maple is weakened with the rot it is susceptible to Verticillium wilt or Pseudomonas.
I hope I have covered all the dos and don’ts. But there is always something else to learn about maples.
Please contact me if you have any questions.
Sam, the Maple Lady
Phone 360.263.2662 Pacific Time – Please check your time.