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Container Garden Containers

The three main considerations when choosing a container for your container garden.

By Thomas J. Fox

tomato container garden

Photo courtesy of Digital Vision/Martin Poole/Thinkstock

One consideration when starting your container garden is using plastic pots.

Excerpt from Urban Farming by Thomas J. Fox with permission from its publisher, Hobby Farm Press, an imprint of BowTie Press. Purchase Urban Farming here.

There are three main considerations when choosing a container for your container garden.

1. Drainage: The container must have adequate drainage so that air can get to the roots of your plants, unless you are planning on growing aquatic plants.

2. Volume: In general, the greater the container’s volume, the better; a big container is better.

3. Construction material: Involves both function and aesthetics

For the most part, there are four main options for a container plant container: pottery, metal, wood and plastic.

Pottery can be very attractive, but it has a number of significant downsides for the active urban farmer. For one thing, pottery is very heavy. A 2 1/2-gallon glazed pot might weigh 10 pounds empty and the soil will weigh another 20 pounds or so. Add a plant and water, and that’s a container garden you’ll rarely want to move.

Unglazed pottery, such as terra cotta, may be a bit lighter, but its porosity can cause significant water loss through evaporation. That can be OK for dryness-loving houseplants and herbs, but many vegetables are a thirsty bunch.

In addition, pottery is more breakable than you might want for an urban farm that you expect to be heavily trafficked. Ceramic pots are particularly susceptible to cracks in colder zones through freeze/thaw cycles. Metals are suitable for garden containers, from a physical perspective. Metal containers are strong, relatively light and not porous. From a chemical perspective, however, many metals can be problematic. Aluminum, copper and zinc can all be toxic to plants.

Copper looks great, can develop a nice verdigris, and is sometimes used in crop fungicides, but it can also be very toxic to plants — check out the ingredients of root killer.

Brass is comprised of copper and zinc, both dangerous.

Bronze contains copper and sometimes aluminum.

Galvanized steel contains zinc and can be contaminated with cadmium, which may be fine for plants but not so much for you. According to the Centers for Disease Control and Prevention, high doses of cadmium over a short period “severely irritates the stomach, leading to vomiting and diarrhea,” while low doses over a longer term can lead to cadmium buildup, kidney disease, lung damage and fragile bones. Whether or not a metal’s potential harm will actually be a problem depends upon a lot of factors. So unless you’re a chemist and know better, I’d recommend avoiding metal, with possible exception of stainless steel if you can find it.

Wood is relatively tough, light and cheap — all attractive qualities for containers for container gardens. It’s even organic — in the sense that it contains carbon and has been alive, if not in the sense that it grew without synthetic inputs.

The problem is that wood rots. You can buy treated wood or preserve it with chemicals yourself, but then you have to weigh the safety of the additional chemicals in your growing container against the value of prolonging a wood container’s useful life. Half-barrels are often charred to prevent rot, which is preferable to chemical additives if you’re planning on growing food.

Whatever kind of wood container you use, make sure it drains well.

Another solution is to line the inside of the wood containers with something impermeable, which takes us to the next option: plastics. You can even buy plastic liners for those half-barrels to make a fish pond or long-lasting planter.

Plastics are probably the most flexible of container materials for container gardens. They can be extremely light, exceptionally strong and have just about any appearance. Many, but not all, are recycled.

If you are going to use plastic, however, consider making two practices part of your life. First, reuse what you can — those plastic kitty-litter buckets being a perfect example. Even though the plastic itself may be recyclable, reuse eliminates the energy (of manufacture, shipping and sale) and resources used to make the new container you would otherwise purchase, as well as the resources involved in the recycling process itself.

Second, if you do buy plastic containers, try to buy easily recycled kinds, such as polyethylene terephthalate (PET, indicated by the number 1 in the triangle on the bottom of a container) or high-density polyethylene (HDPE, number 2 in the triangle). Whatever you buy, use the container to death.

One caveat: Avoid reusing plastic containers that have contained potentially harmful chemicals, such as solvents. You can reuse ones that have held salts (halite, for example) after you clean them thoroughly.

The simplest plastic container is a bag of soil. Punch a few drainage holes near the bottom of the sides, cut a slit in the top, and plant directly in the bag. You can buy specialized grow pots to facilitate things, but you don’t need them.

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Look on any material safety data sheet and you will see that zinc is used in making galvanized steel. Zinc is the element in question here with galvanized steel containers and gardening.

Zinc is the 27th most abundant element in the Earth’s crust.

It naturally exists in air, water, soil, and the biosphere. Most rocks and many minerals, as well as humans, plants and animals contain zinc in varying amounts.

In fact, approximately 5.8 million tons of zinc naturally cycles through the environment annually by plant and animal life, rainfall, natural phenomena, and other activity.

Zinc is also common and essential to all life. All living things from the tiniest micro-organisms to humans require zinc to live as it helps with specific metabolic processes.

The minimum daily requirement for zinc is 15 mg, and it is fairly common to take 100 mg per day for short periods to help ward off colds and flu.

Zinc blocks more UV rays than any other single ingredient used in sunscreen and helps with a baby's sore bottom.

People collect rainwater off of galvanized roofs for rainwater collection and then store that rainwater in galvanized steel tanks.

Water districts use larger galvanized tanks to hold public drinking water while most cereals and grains that you buy in the grocery were stored in galvanized steel silos before being processed into Wheaties, etc.

Zinc is all around us and is in much of what we drink and eat. Again, it is a required part of our diet.

But even so, it has been shown in testing that zinc does not leach into the plants growing inside galvanized containers.

A group of professors at The University of California tested plants growing inside galvanized containers.

After this testing, the group has no concerns about zinc leaching within the containers. Even when zinc does show up at low trace levels in soils, the leaves and fruits of plants test negative.

Bottom Line: you will be hard pressed to find zinc in the soil within any galvanized steel garden, and you will not find the zinc within the plants themselves.

But if you are still have concerns then there are certain paints, coatings and liners that can adhere to the inside of your garden
John, Austin, TX
Posted: 8/8/2015 5:25:01 AM
I use plastic 18 gallon totes. Cheap, works for one or two seasons, and super easy to move around the yard
Denise, Przybylowicz, TX
Posted: 4/12/2015 3:27:17 PM
Posted: 2/18/2015 4:39:51 AM
I live in sand on the Central Coast of California. It is too cool here for tomatoes so I buried large pulp pots in the sand, up to their rims, filled them with good compost, planted my tomatoes (Sweet 100 and San Marzano)and then topped them with 3.5' high clear plastic tubes I found online. The tubes came without any air vents so I slapped on some duct tape and cut holes. So far, so good. I am harvesting the best Sweet 100s I've been able to grow in my ten years here. The San Marzonos look terrific but are still green. I am hoping the pulp pots will last 2-3 seasons.
Diane, Los Osos, CA
Posted: 7/13/2013 2:43:32 PM

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