Using Plastic Containers to Plant Perennials Outside

(Question)

Hi!

I have 5-7 Double Size 7-eleven slurpy plastic cups. I want to use them to grow perennials next year. Of course I will be puncturing holes at the bottom of each cup to allow water to flow freely down the earth.

The reason for my using the cups is that the area I will be planting flowers has a lot of deep-rooted roots – probably from weed?

So, I was thinking that weed can’t escape into the plastic pots and disturb flower growth. And the weeds are free to grow around the plastic containers (if they wish).

I hate weed. I’d love to suppress it especially when I want to grow something as colourful as flowers.

So, what do you think about me digging down to just a little less than the height of the plastic cup (all same size).

Of course, what to do with the extra dirt?

And yes, I’ll need to get the soil winter ready. This is a question for the next time.

(Answer)

Thank you for contacting Toronto Master Gardeners.

Perennials thrive when they have good soil to grow in, water and oxygen available to the roots and a good supply of nutrients. The roots of the perennial grow out and down creating a solid support system for the above ground portion of the plant . Restricting root growth to the size of the cups will not allow your plants to create this support system. With the cup buried in the ground, even with holes in the bottom it will not drain properly as the holes are restrictive and up against more soil with a different a density. This will lead to the air pockets in the soil being filled with water and can drown the roots. The nutrient supply to the roots within the cups is finite and will be quickly depleted.

If the roots in the garden bed are indeed to difficult to remove then you may want to consider a raised bed. When creating a new bed you can first lay something compostable ( like newspaper or cardboard) on the ground to slow down the growth of the roots from the original bed. This layer will slowly breakdown and add nutrients to the soil. The new raised bed can be added on top of the paper layer. If you mulch around your perennials once they are planted it will help keep down the growth of new weeds and hold moisture in the soil so you do not need to water as often.

Good luck and I hope this helps.