Consider the Characteristics of Containers

Plants in containers

Plants in containers

I was in the veterinarian’s office the other day and I noticed that they had a sickly looking little plant in a pot on the windowsill. Being the ever-helpful type I am, I asked them if they needed a hand with the little fellow. The vet tech told me to help myself, but she didn’t think the little plant stood a chance. After taking one look, I could tell what was wrong, and it was probably terminal. That little plant was potted in the wrong kind of container—it was cute, but it had no drainage holes and the soil looked like it had been constantly saturated. The sick little plant most likely had root rot, and although I was sad for it, it got me thinking about pots.

We’ve talked about soil and equipment and plants in this blog, but we’ve yet to discuss pots. With seedling season upon us, I figured there wasn’t a better time to write this particular piece, since you’re soon going to be storming the aisles of your local nursery supply, hardware store or big box outlet in search of all the stuff you need to start your seedlings. I want to make sure you’re armed and ready to pick the right pots so your seedlings will have a much better chance of success than that sad little plant in my veterinarian’s office.

The properties of pots

Pots serve the same function, no matter what they’re made from, but they’re not the same—far from it—and the characteristics unique to certain materials can work better for specific plant species. The two main pot features you need to be concerned with are the drainage and porousness, though other things like biodegradability and insulating ability can be important, too.

Drainage is easy—it’s all about how quickly water you pour in comes out the bottom. There are pots with excellent drainage, pots with poor drainage and pots with no drainage. Most plants can’t survive in any but the first of these, though some hardier specimens may linger for a very long time. Even bog plants do better if you can control how much water remains standing in their pots.  When you’re shopping for pots, leave behind anything without either a large central drain hole or several smaller holes distributed across the bottom. Root rot and damping off disease aren’t fun and once they set in, are nearly impossible to cure.

Porousness is a little harder to see than drainage. Pots are made out of lots of different materials, from compressed peat and cow manure to stone, metal and ceramic and everything in between. Some of these are porous materials—that is, they allow water to readily pass through the walls—like clay, peat and cement. Others are non-porous, including glazed ceramic, plastic and metals. This matters because plants that can’t tolerate being wet will dry out faster in porous pots—that’s why cacti tend to be potted in clay, it’s not just for looks. The same applies in reverse, of course. African violets, for example, like soils that stay a little moist, so they tend to be potted in plastic to make it easier to maintain those conditions.

Choosing the right pots for the job

Picking a peck of pickled pots can get a little tricky, especially if you’re not really sure what your plants need since they’re new to your greenhouse. I’ve tried to simplify that process for you by breaking down the most common container types and explaining their properties and pros and cons.

Cement – Nice-looking, long-lasting porous pots perfect for planting things in areas where there may be concern of tipping or theft. Cement pots weather fairly well and will last almost forever if you take care of them, but they aren’t always cast with drainage holes so you must choose these pots with care. Also, their weight and porous nature make disinfecting cement containers a massive headache.

Clay – Easy to find and cheap, clay pots get heavy and fragile as they increase in size, so they’re a poor choice for large applications. They’re extremely porous, though, and excellent choices for plants like cacti and orchids that need to be able to get a quick drink and rapidly lose the rest of the water they’re given. I love clay pots, but they have their limits.

Compressed peat – In my opinion, compressed peat is the only way to go for seedlings. These pots are lightweight, plantable and change colors when they start to get dry, simplifying watering chores. However, they do dry out quickly and can start to melt if you keep them in the greenhouse too long.

Geotextile –  The idea of geotextile pots is still somewhat new, but it’s a neat concept—the Smart Pot is just one example. These pots are made of the same stuff you’re using for weed fabric, so they’re extremely porous, but lightweight and durable. Honestly, I’ve never used these, but I can see how they would be a real pain to keep watered since you’re basically growing in an unprotected pile of dirt.

Glazed ceramic –  Heavy but beautiful, glazed ceramic pots will stand up to the elements for years to come provided they’re protected from hard freezes and tipping. They’re non-porous, but don’t always have the best drainage, so evaluate glazed ceramic pots carefully before bringing them home for planting. You may be able to cut more holes with a masonry drill bit, but do so carefully.

Metal –  Perhaps the worst material on the planet for housing growing plants, metal pots are non-porous, hold on to heat and frequently rust, making them a difficult sell for me. That being said, I own several old washtubs that I plant annuals in every year, so they can have their places if you choose galvanized or non-reactive metals with excellent drainage and protect them from heat. You’ll need to empty metal pots every few years to check for rust for best results, though.

Paper – Recycled newspaper pots are popular for seed starting, and I can’t say that there’s a lot of problem with this—theoretically they’re biodegradable (there is some research that says under certain conditions they might not break down as well as we hoped), they’re semi-porous and they can be crafted into a number of sizes to accommodate your needs. Like compressed peat, you can’t count on these guys for the long haul because they’ll melt after too many waterings.

Plastic/fiberglass – A good two-thirds of my planters and pots are made of plastic or fiberglass, so I’m a bit biased, but these materials are generally pretty good all around. They’re non-porous, easy to cut new drainage holes into and come in a huge range of sizes, colors and styles. I don’t start seeds in plastic, though, because they can be tough to get out without damaging young roots. Darker plastic pots can also get very hot in the summer.

Reused Materials – NO. Just, no. I’ve been on Pinterest, I know what you guys are doing with old boots and used jeans and little red wagons. Please, just stop. There’s a reason there aren’t pots made of the kinds of materials that are being recycled, and usually it’s because they either rot or rust when constantly in contact with wet soil. Reason number two is that they might contain toxic chemicals like lead that aren’t great for your plants or you. Last, but not least, most of these things don’t drain well.

Wood – Wood’s a tricky material, to be sure. There are applications for wooden containers, to be sure, but the semi-porous material isn’t used as much as it used to be. Today it appears more often in the form of whiskey barrels and raised bed garden frames, where it shines brightly for a few years—often poorly prepared wooden containers like these decompose due to the constant pressure of wet soil. However, wood is also versatile, so if you seal your wooden containers and periodically empty them out to refresh that seal, they could last a very long time. Drainage holes are easy to cut and treated wood weathers beautifully.

[box]by Kristi Waterworth[/box]

image: Rachel Strohm via Compfight cc
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