Will Plastic Bottles at the Bottom of Large Flower Pots Harm Plants?

Soil Volume

• If the plastic bottles take the place of a large part of the volume of the container, leaving insufficient room for soil, they could harm your plants. Too little soil volume may cheat your plants out of nutrients and the support they need. Tall, weighty plants may become top-heavy and tip over, particularly under windy conditions. Select bottles that fit the relative size of your container, but leave plenty of room for soil depth and width. Keep in mind that larger plants will need a greater depth and volume of soil.

Root Growth

• Plastic bottles can impede root growth if they are placed in the zone where your plants' roots will grow. Research the soil depth needed for the plants you want to raise. For general planting, place soil around the bottles and then add a 6- to 12-inch-deep layer of soil above the bottles to give your plants' root systems plenty of room to expand. If your plant forms a taproot, arrange the bottles around the outside edge of the container to allow the taproot to grow down between the bottles. This will provide an additional few inches of soil depth as well.

Trapped Water

• Plastic bottles could create a reservoir at the bottom of your planter, trapping water that should drain away. If your plants' roots remain wet, they could develop issues with rot, which can kill plants. Avoid using open-mouthed bottles or bottles cut to fit the container. Use bottles with the caps firmly in place. Make sure the bottle arrangement does not block drainage holes in the bottom of the planter.

Leaching

• For the most part, plastic bottles resist decay and should not shed harmful substances into the soil. The eBottles website disputes many of the common fears over chemicals leaching from plastic bottles; however, if you still have a concern, only use the bottles in connection with plants not used for food or choose bottles that do not contain phthalates, BPA or PET. To be on the safe side, use bottles made for drinks or food, rather than bottles made to store chemicals or poisonous substances.

Bioplastics

• Bioplastics are made to break down and decay readily, so this type of bottle may not work well in the bottom of a planter over the long term. Outside of composting conditions or direct sunlight, the bottles may only partially break down or do so slowly and unevenly. Even under composting conditions, bottles made by Biota require 80 days to biodegrade, so you may risk their use in planters where you plan to place annuals and biennials or to temporarily house perennials.