In some climates, it’s easier to grow vegetables and dwarf fruit trees in plastic pots or containers rather than the ground. Such is the case in the higher elevations of Colorado Springs where the winters are long, the ground is very compacted, and the dry summer winds sap moisture from the leaves and the ground. Very little grows naturally in this area, except a small variety of weeds, grasses and the ever resilient Cottonwood tree.
For these reasons, many of us in this area grow our vegetables and small dwarf fruit trees indoors for part of the season in plastic pots or containers. When positioned in brightly lit windows, preferably with direct sunlight, smaller vegetable plants will grow just fine. It’s also a good way to get them started early until such time that they can be transplanted outside into raised garden beds or greenhouses.
Or, as is the case with my dwarf lemon and lime fruit trees, they remain in their plastic pots indefinitely. In the summer months, I move them outside while in the cooler months, I moves them inside. Which brings up the question; is it safe to grow vegetables and fruit in plastic containers?
Are Plastic Pots Safe?
The answer is, yes. But there are a few things you need to be aware of.
First and foremost, knowing what was previously in the plastic pot is critical. If it held oil, chemicals, cleaning fluids, or any other toxic substance, then don’t use it! No matter how much you clean the pot, it’ll never be safe for growing food. Plastics can absorb the chemicals later releasing them into the soil. Plant roots can then uptake the chemicals contaminating the food your are growing (and want to eat).
Secondly, knowing the composition of the plastic is important. Some plastics are OK, while others can break down and release chemicals that could be dangerous to your health. More on this below.
Thirdly, try to keep plastic out of extreme heat. For example, a black plastic pot in direct sunlight can exceed 100F. At this temperature — over a long period of time — some plastics can start to break down into other chemicals which may be hazardous to your health. Many of the plastics used today just haven’t been around long enough to know of the long term affects. For the longest time, BPA was considered safe. Only later we found out it’s not. So it’s better to error on the side of caution.
Which Plastic Pots Are Safe?
If you look on the bottom of a plastic pot, you should see a small triangle symbol with arrows. Inside the triangle is usually a number or some letters (see image to the left). They all indicate different types of plastics.
The numbers safe for growing food are 1, 2, 4, 5. Never use plastic pots containing the number 3, 6 or 7. Fortunately, most of the pots I see in the gardening sections of Home Depot or Lowe’s are HDPE (2) or PP (5), which are considered safe.
The PETE (1) plastic is used in clear bottles. It’s really meant for one-time use and will break down over time. It will absorb its liquid contents which makes it really important you know for sure nothing dangerous was ever stored in it.
The HDPE (2) plastic is used in milk jugs, juice and water containers sold in stores. It’s meant to break down into non-harmful bi-products over a very long period of time. Despite this, it’s a good, safe option.
The LDPE (4) plastic is used in squeeze bottles and plastic bags. It too is safe, but will break down if left out in the sun. I haven’t seen many pots with this marking.
The PP (5) plastic is used to make caps and lids and is more sturdy than the others. It also has a much higher melting point and can be “hot-filled” without breaking down into another substance. Recent studies have found no evidence this type of plastic leaches any chemicals into food (source: Livestrong). This is probably the most ideal long-term plastic container for growing food.
What Other Plastics Should Be Avoided?
Do not grow food in containers made of PVC or any plastics that contain Phthalates. This is kind of tricky because Phthalates aren’t a single chemical. They’re an entire family of them, and they don’t all behave the same way. Three of them in particular are BBP, DBP, and DEHP, which have been banned from toys and items used by toddlers under the age of 3 years old. Some recent studies on animals show Phthalates can disrupt hormones (source: WebMD). What’s not clear is how much is considered dangerous in a human body. Again, it’s just better to error on the side of caution.
Stay away from any plastics that contain BPA, which stands for bisphenol A. This an industrial chemical that has been used to make certain plastics and resins since the 1960s and is now widely considered unsafe (source: Mayo Clinic). Fewer manufacturers are using plastics with BPA, but plastics with the V (3) and OTHER (7) markings could still contain this chemical. If the pot looks really old, don’t use it.
Lastly, any container that is not clearly marked should never be used for growing food.