Peat pots come in various sizes and shapes. Source: www.greenhousemegastore.com
In this season when so many gardeners are starting their flowers and vegetables indoors, here are some thoughts on the “peat pots” commonly used as containers for seedlings.
Several seedlings (zinnias, melons, castor beans, etc.) have fragile roots and can suffer during transplanting if you sow them in plastic pots or cell packs because this exposes their root ball to damage as you try to replant them. This is where peat and other biodegradable pots come in.
Typically, these round or rectangular pots are made of pressed peat with a bit of added wood fiber. Note, though, that many so-called peat pots no longer contain any peat at all. Coir (coco fiber) pots have replaced peat ones in sort parts of the world and one manufacturer even produces “cow pots” made of pressed cow manure! In gardening lingo, though, they’re all still called peat pots!
Roots grow right through the sides of peat pots. Source: www.hobbuysell.com
All these biodegradable pots are strong enough to use as plant pots, but unlike plastic pots, they are porous, letting air and water circulate … and also allowing the roots of your seedlings to grow through them. You’ll actually see the roots penetrating the wall of the pot as they grow. You’ll find both individual pots and “strips”: lengths of square pots linked together.
Add water to a peat or coir pellet (on right) and it will expand into a pot (left). Source: university.upstartfarmers.com
Pots That Grow
You’ll likewise find “pellet pots.” Hard and flattened when you buy them, they expand into pots when you soak them in water. They’re made of peat or coir through and through, with only a thin fiber netting on the outside, so are already full of “soil” when they expand: you won’t need to add any seedling mix. I must admit that I’m not a great fan of pellet pots: I find them very dense and poorly aerated and also, they tend to stay too moist for my taste. I prefer to use regular peat pots I can fill with a lighter, better draining seedling mix, often simply a locally available commercial one. However, everyone’s growing conditions are slightly different and they may work well for you.
Fill and Sow
To use peat pots, simply fill them with your favorite seed-sowing mix and moisten well before sowing. Then sow the seeds, water and take good care of the seedlings until planting time. When that time does come, all you have to do is to plunk the pot into a planting hole, without removing the pot, and cover with soil. Water well … and your seedlings will continue to grow without slowing down, as they were never subjected to transplant shock. Not only will the roots grow right through the walls to establish themselves in the surrounding soil, but the pot itself will decompose over time, leaving no trace in the soil, although that can take a year or more.
Homemade Biodegradable Pots
You can turn various products around your home into biodegradable pots, like these recycled toilet paper tubes. Source: www.thriftyfun.com
You can also cheaply make your own biodegradable pots, usually from some sort of paper product. Toilet paper and paper towel tubes (the latter cut in three) will hold soil if you fold the bottom in. They are biodegradable, although a bit small for some seedlings. And they do tend to become covered with icky mildew (more on that later). Cardboard egg cartons also make decent if, again, rather small biodegradable pots. You can also turn newspaper into biodegradable pots using a tool called a potmaker.
Strange Advice
Using biodegradable pots is so simple you might wonder why I’ve even bothered explaining how to use them, but … there are always people who manage to get it all wrong and then proudly publish their errors on the Internet.
One bit of false information I often see on the Net is that peat pots are harmful to seedlings because, being permeable and absorbent, they “steal water” from the seedlings. Now, that is technically correct: they do absorb a bit of water, certainly more than a plastic pot (it uses none), but that’s actually a good thing, not a flaw!
Notice how the planted peat pots to the right are starting to dry out, but are not yet as pale as the unused pots. They aren’t quite ready to water. Source: gardenclub.homedepot. com
You see, for seedlings to grow well, their potting mix needs to at least start to dry before it is watered again. As soil dries out, this leaves tiny air pockets in the mix and that “pulls” oxygen—necessary for root growth—into the root zone, a major plus for your seedlings. That’s why you actually wantyour growing mix to dry out just a smidgen before you water again.
Seedlings in plastic pots require more careful monitoring, because it’s not easy to see whether their soil is moist, just a bit dry (bingo! time to water!) or very dry (not good for seedlings). As a result, we tend to water more than we should, often before the seedlings needed more moisture, leaving the roots oxygen-starved. Also, the impermeable walls of plastic pots slow the flow of oxygen to the roots.
Biodegradable pots, on the other hand, change color dramatically from dark brown to pale brown when they reach the point where they are nearly dry and need to be watered again. So you know at a glance when they are ready and there is therefore less risk of watering too early. In addition, oxygen more readily penetrates their permeable walls.
There is no logical reason to pull the bottom off a peat pot … yet this advice is widely shared on the Internet. Source: my garden.blog
Here’s another bit of dumb advice you’ll read on the Web: “you have to tear the bottom off the peat pot before planting so the roots can grow down into the soil.” Wait a minute! The roots are already growing through the bottom of the pot. If you remove it, you’ll damage them … and didn’t we just say biodegradable pots are designed specifically for plants that have fragile roots? Just plant the whole pot: there is no need to tear the bottom off and risk harming your seedlings!
Worse yet, some people suggest peeling the entire peat pot off. Yet more nonsense! If you intend to remove a pot at planting time, why use biodegradable, one-time-use pots at all? Plastic pots and cell packs are much easier to remove and can be reused year after year, so are therefore cheaper. Use them if your eventual goal is to remove the pot.
Correct Advice
When you plant a peat pot, the entire pot must be buried. If any part of the pot rim remains above the surrounding soil, pull or cut it off. Source: dewharvest.blogspot.ca
There is something you might want to tear off a peat pot, though. When you transplant the seedlings in peat pots, you have to be careful to bury the entire pot. If the top edge sticks out of the ground, it will, under certain circumstances, act as a wick and dry out the root ball. So if any of the pot does show aboveground and you’re not going to be covering it with a mulch, yes, by all means tear or cut that part off.
Mold Concerns
The white mossy growth seen on this pot edge is mold … and it’s not harmful to the seedlings. Source: The Garden Hub
Another complaint you hear is that fungi can form on peat pots and indeed, you do sometimes see a little “mold” (fungus) on pot walls. This is most common on pots that are always kept soaking wet and you can avoid it in many cases by letting the pot dry out a bit before you water again … something you should be doing anyway!
Even so, these fungi are rarely harmful to plants and may even be beneficial (the white mold you see integrated into pot sides is often the mycelium of mycorrhizal fungi, friendly fungi plants need in order to grow well). What do you expect? Peat pots (or coir or cow manure pots) are natural products and fungi will grow on them, especially over time. What can I say? When you use natural products, you have to expect natural results! I just ignore the fungus and have never had problems with it.
I find paper pots (notably toilet paper pots) especially subject to mold. If that bothers you, use something else.
For Use on Fragile Seedlings Only
Let me repeat something before closing: peat pots are an added expense to growing plants from seed and one of the main reasons gardeners sow seeds is to save money. Commercial peat pots offer no benefit whatsoever to the majority of seedlings compared to plastic pots or cell packs. It is simply wasteful to sow tomatoes, petunias, marigolds, and most other garden plants in peat pots unless they are ones you made yourself out of recyclable materials. Instead, reuse and recycle other containers for use in starting seedlings. Keep one-use-only peat pots for those seeds whose fragile roots would otherwise make transplanting difficult.
Seeds That Need Biodegradable Pots
The following plants are ones that would benefit from sowing into peat pots. All have roots that are either very fragile and therefore absolutely need to be sown in biodegradable pots or fragile enough that they can be set back if the root ball is mishandled when transplanting.
Hello! I’m fairly new to gardening and decided to start my own seeds this year. I chose biodegradable peat pots and I am finding black mold under a few of them- not many. Should I dispose of those seedlings or simply transplant them to a new pot? Thanks for your help!
Don’t worry about it. It’s simply normal decomposition. The pot is designed to decompose and the mold is just giving it a head start. It will hold together long enough for you to plant it.
Regarding Castor Oil Plant (ricinus communis)
It is a perennial and toxic—to the point of lethal. It is considered
A quick summary from Wikipedia:
“The toxicity of raw castor beans is due to the presence of ricin. Although the lethal dose [no known antidote] in adults is considered to be four to eight seeds, reports of actual poisoning are relatively rare.[26] According to the Guinness World Records, this is the world’s most poisonous common plant.[27] Symptoms of overdosing on ricin, which can include nausea, diarrhea, tachycardia, hypotension and seizures, persist for up to a week. However, the poison can be extracted from castor by concentrating it with a fairly complicated process similar to that used for extracting cyanide from almonds.
“If ricin is ingested, symptoms commonly begin within 2–4 hours, but may be delayed by up to 36 hours. These include a burning sensation in mouth and throat, abdominal pain, purging and bloody diarrhea. Within several days there is severe dehydration, a drop in blood pressure and a decrease in urine. Unless treated, death can be expected to occur within 3–5 days; however, in most cases a full recovery can be made.[28][29]
“Poisoning occurs when animals, including humans, ingest broken castor beans or break the seed by chewing: intact seeds may pass through the digestive tract without releasing the toxin.[28] The toxin provides the castor oil plant with some degree of natural protection from insect pests such as aphids. Ricin has been investigated for its potential use as an insecticide.[30] The castor oil plant is also the source for undecylenic acid, a natural fungicide.
Commercially available cold-pressed castor oil is not toxic to humans in normal doses, either internal or externally.[31]”
In addition to its poisonous character, he plant was introdused to the US from Africa. It is invasive, overrunning and displacining native plants.
Thanks for these thoughts. Of course, in most parts of North America, at least, the castor bean is far too tender to ever become invasive, and is strictly used as an ornamental annual.
Thank you for the information. It was quite helpful and explains a lot. In my experience with transplants, I noticed that if you transplant a delicate plant to a pot with potting soil, it takes quite well as the soil is similiar. For example dill and fennel both died in my garden when I placed it in the ground, but did well in my containers. Other plants such as zucchini and cucumber, do not die necessarily, but can take a long time to establish in the garden. Yet other plants, such as carrots, definitely do not transplant well. I bought some last year planting them in a container, and they were all deformed when It came time to harvest.
Good advice about peat pots, but I wonder how valid the point is about plants that don’t like to be transplanted? I grow a lot of plants from seed and use plastic pots. I have grown just about all of the perennials and trees on your list without problems at transplant time ( I don’t grow annuals). Even the difficult to grow Baptisia will do just fine in a pot. https://www.gardenmyths.com/growing-baptisia-australis-from-seed/.
I actually didn’t include many trees, shrubs and perennials, as most really don’t mind transplanting. But it can throw off some of the faster-growing plants. It will stop a Ricinus dead in its tracks, for example. And the taproot plants (carrots, beets, etc.) won’t produce a taproot. (You might wonder why anyone woulds start carrots and beets indoors, but if you lived in, say, Chicoutimi, with its even-so-short growing season, you would). You can grow many of the plants listed in regular pots if you’re very careful, but why risk even a short delay when summers are so short?
Hello! I’m fairly new to gardening and decided to start my own seeds this year. I chose biodegradable peat pots and I am finding black mold under a few of them- not many. Should I dispose of those seedlings or simply transplant them to a new pot? Thanks for your help!
Don’t worry about it. It’s simply normal decomposition. The pot is designed to decompose and the mold is just giving it a head start. It will hold together long enough for you to plant it.
Thank you! ??
Regarding Castor Oil Plant (ricinus communis)
It is a perennial and toxic—to the point of lethal. It is considered
A quick summary from Wikipedia:
“The toxicity of raw castor beans is due to the presence of ricin. Although the lethal dose [no known antidote] in adults is considered to be four to eight seeds, reports of actual poisoning are relatively rare.[26] According to the Guinness World Records, this is the world’s most poisonous common plant.[27] Symptoms of overdosing on ricin, which can include nausea, diarrhea, tachycardia, hypotension and seizures, persist for up to a week. However, the poison can be extracted from castor by concentrating it with a fairly complicated process similar to that used for extracting cyanide from almonds.
“If ricin is ingested, symptoms commonly begin within 2–4 hours, but may be delayed by up to 36 hours. These include a burning sensation in mouth and throat, abdominal pain, purging and bloody diarrhea. Within several days there is severe dehydration, a drop in blood pressure and a decrease in urine. Unless treated, death can be expected to occur within 3–5 days; however, in most cases a full recovery can be made.[28][29]
“Poisoning occurs when animals, including humans, ingest broken castor beans or break the seed by chewing: intact seeds may pass through the digestive tract without releasing the toxin.[28] The toxin provides the castor oil plant with some degree of natural protection from insect pests such as aphids. Ricin has been investigated for its potential use as an insecticide.[30] The castor oil plant is also the source for undecylenic acid, a natural fungicide.
Commercially available cold-pressed castor oil is not toxic to humans in normal doses, either internal or externally.[31]”
In addition to its poisonous character, he plant was introdused to the US from Africa. It is invasive, overrunning and displacining native plants.
Thanks for these thoughts. Of course, in most parts of North America, at least, the castor bean is far too tender to ever become invasive, and is strictly used as an ornamental annual.
Thank you for the information. It was quite helpful and explains a lot. In my experience with transplants, I noticed that if you transplant a delicate plant to a pot with potting soil, it takes quite well as the soil is similiar. For example dill and fennel both died in my garden when I placed it in the ground, but did well in my containers. Other plants such as zucchini and cucumber, do not die necessarily, but can take a long time to establish in the garden. Yet other plants, such as carrots, definitely do not transplant well. I bought some last year planting them in a container, and they were all deformed when It came time to harvest.
Your observations are very just. And most root vegetables – not just carrots – really should not be transplanted at all!
Good advice about peat pots, but I wonder how valid the point is about plants that don’t like to be transplanted? I grow a lot of plants from seed and use plastic pots. I have grown just about all of the perennials and trees on your list without problems at transplant time ( I don’t grow annuals). Even the difficult to grow Baptisia will do just fine in a pot. https://www.gardenmyths.com/growing-baptisia-australis-from-seed/.
I actually didn’t include many trees, shrubs and perennials, as most really don’t mind transplanting. But it can throw off some of the faster-growing plants. It will stop a Ricinus dead in its tracks, for example. And the taproot plants (carrots, beets, etc.) won’t produce a taproot. (You might wonder why anyone woulds start carrots and beets indoors, but if you lived in, say, Chicoutimi, with its even-so-short growing season, you would). You can grow many of the plants listed in regular pots if you’re very careful, but why risk even a short delay when summers are so short?