Container Ideas: Upcycling Plastic
Growing microgreens can be an easy low-cost activity if you look for your materials in the right places. Let’s upcycle some of your plastic containers from the grocery store to grow your own fresh food in the form of microgreens.
In general, if you're starting with a hard plastic container that was made to store food, then it is probably safe to grow microgreens in. It ultimately seems to depend on how the item was made and what it was made for. Some items are made to be one-use and break down much faster, some items are made to hold up for much longer. Most of these containers are made for one-time usage, so I would limit the number of uses before recycling in favor of a new container.
When looking at plastic containers to use for growing microgreens, one clue into the type of plastic that it is made of is on the recycle symbol on the container. According to my research, you ideally want to use a plastic container that has the numbers 2 (HDPE), 4 (LDPE), or 5 (PP). I’ve personally never seen a suitable container made from LDPE, but several that were HDPE or PP. You want to stay away from (3) PVC and (6) PS when it is in styrofoam.
Let’s take a look at some of the upcycled containers I use.
When upcycling plastic containers, I look ideally for containers that are not only safe for food, but safe for hot foods. These plastics seem to have an extra layer of protection that prevent anything from leaking at any temperature.
I picked up a rotisserie chicken from the grocery store one night and noticed it was a nice shallow container that I’d be able to grow a sizable amount of microgreens in. The plastic was labeled as a 5 (PP) on the recycle symbol. This means it is made from polypropylene. Polypropylene is a tough plastic that will hold up to higher temperatures.
This container fits the necessary specs nicely. It is about two inches deep. And it has a nice lid that will hold in humidity during the germination phase. I put some small holes in the bottom to help with drainage and it was ready to go.
The next is a milk jug that I have cut a few inches from the bottom. I put a few holes in the bottom for drainage, cleaned it really well, and it was ready to go. The great thing about a milk jug is it is semi-transparent. This helps with seeing just how wet the soil is.
Milk jugs like this are typically made from 2 (HDPE) plastic which is a durable plastic that is food-safe. This plastic tends to break down faster than the other choices here though, so limit the number of uses before recycling in favor of another container.
PET or PETE
This is a salad container that is made from (1) PET. This is used in almost every cold food container that I could find in the fresh section of the grocery store. It is also used in the plastic in bottled water. PET is probably the easiest one to find out the choices here, and it is usually transparent.
I have grown several crops of microgreens in this type of container, and right now I’m using one as a water basin to bottom-up water the microgreens in my milk jug. There’s something oddly satisfying about growing fresh greens in the container that I bought my store-bought greens in. The transparency really helps me to know what is going on with my microgreens.
Despite that, out of all the types of plastic I upcycle, PET seemed to be the most controversial. PET or polyethylene terephthalate seems safe as long as it is not exposed to high temperatures (140+ F) (source). Some opinions were that it was safe, some thought it wasn't. So I mainly use it as water basins for other containers, or as a container for seed packets.
I think it is also worth mentioning that while some plastics mentioned here may leach chemicals at certain temperatures or over certain periods of time, it would be questionable whether any of this would be taken up by a plant.
I love ideas that solve two problems at once. Protecting the environment and growing fresh food is a great way to start any week. Plastic is not at the top of my list of environmentally-safe materials, but reusing it to reduce your need for more grocery store containers is a good way to make it more environmentally-friendly.
A final word on choosing a container. Make sure you know what it was made for or has contained in the past. Certain plastics can absorb some of the materials they are carrying. If the container has carried pesticides, poisons, metals, or chemicals, it could get into your soil and water. Small growing trays can cost as little as a few dollars each, so it simply isn’t worth the risk.
You have to be cautious when upcycling, but it's also a chance to get creative. It can be a quick way to get some microgreens going when you don't have access to more traditional solutions like growing trays.
Want to do your own research on the different types of plastics? Try this pdf from National Geographic.