Hello Dear Master Gardener, Last year we moved to a 70 years old home in Toronto that is facing east. There is a huge brick planter in front of the home, about 3 feet tall, maybe 20 feet wide and about 4 feet deep. The brick retaining wall is tilting and I guess if moisture build up behind the wall, it will fall apart. Thus, the brick planter on one hand is perfect to plant and possibly hide its imperfection, and on the other it might cause more issues. I guess that is why it was filled with mulch when we bought the home. I was thinking to plant Juniperus horizontals. What are your thoughts, suggestions, or ideas. I am very grateful for this opportunity and your time. Warm Regards.
Wow! Lucky you!
Junipers are tough low maintenance plants that can grow very well in containers provided you follow a few guidelines.
As junipers, including Juniperus horizontalis, are drought tolerant and do not like to have wet roots, to thrive in your planter and to try and ensure that the planter walls do not collapse, you should make sure that the planter has good drainage before planting the junipers.
It is not clear from your question whether the brick planter is against your house or otherwise placed in your front yard or whether it has an impermeable base or is open so at the bottom so that water can escape into the ground. The latter would be ideal. However, as you indicate that the brick retaining wall is tilting, the drainage behind the wall is probably less than idea and you should consider taking steps to improve it. Before taking any action, I suggest you test the drainage of the soil in the planter. Soil drainage is usually tested by a “perk” test, made by digging a hole, filling it with water and then determining how long it the water to drain out of the hole. Here is a link to an informative article from Iowa University Extension on testing and improving soil drainage: https://hortnews.extension.iastate.edu/testing-and-improving-soil-drainage
In addition to soil amendments to improve drainage, if the drainage is poor you could consider adding a footing drain and gravel layer at the base of the wall, as well as weep holes along the wall, which will improve drainage and may prevent further collapse. While this type of work should be done when a retaining wall is being built it can be done at a later date by a knowledgable individual. If none of your family members are handy with this sort of work, I suggested contacting a local handy person with experience with retaining walls, or a member of Landscape Ontario https://landscapeontario.com/ with such experience.
Other than good drainage, junipers require partial or full sun. You indicate that the house faces east, but not whether the area where the planter is located is mainly shaded. If the latter, it would probably be best to consider another plant. However, if you have at least six hours of sun a day you should be able to grow junipers.
Here is a link to a previous Toronto Master Gardener question on junipers which discusses the desired soil conditions and how to plant: https://www.torontomastergardeners.ca/askagardener/skyrocket-junipers-dying-in-clay/
Depending on the cultivar, each plant can attain a width of up to 5 feet. As your planter is 20 feet wide you are going to have to get a number of plants to fill the planter. You should consult with your garden centre to determine how many of the cultivar(s) you have chosen are required for the area of your planter. Note that there are online plant spacing calculators if you want to make this determination yourself. Juniperus horizontalis is a slow growing plant. During the period while you are waiting for your junipers to mature, you could consider interplanting them with other plants which like the same growing conditions – slightly acidic dry soil, plenty of light and very good drainage – and which would look well with the junipers you have chosen – based on the shape and height of the other plants, the colour of the leaves of the juniper you have chosen and the leaves and flowers of the other plants. As there are many cultivars of Juniperus horizontalis to chose between, you might also consider planting a number of different cultivars to add visual interest to your planter.
This is an interesting project. Good luck!
Sept. 25, 2022