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!
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.
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 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.
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!
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 want your 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.
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.
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.
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.
- Amaranth or love-lies-bleeding (Amaranthus spp.)
- Amsonia or bluestar (Amsonia spp.)
- Anise (Pimpinella anisum)
- Annual phlox (Phlox drummondii)
- Bachelor’s buttons (Centaurea cyanus)
- Baptisia or false indigo (Baptisia spp.)
- Bean (Phaseolus spp. and others)
- Bean, Hyacinth (Lablab purpureus, syn. Dolichos lablab)
- Bedding lobelia (Lobelia erinus)
- Beet or beetroot (Beta vulgaris Condivita group)
- Bells of Ireland (Moluccella laevis)
- Black-Eyed Susan Vine (Thunbergia alata)
- Blue lace flower (Trachymene coerulea, syn. Didiscus coerulea)
- Burning Bush (Bassia scoparia, syn. Kochia scoparia)
- Cabbage (Brassica oleracea)
- California poppy (Eschscholzia californica)
- Candytuft, Annual (Iberis amara)
- Carrot (Daucus carota)
- Castor oil plant (Ricinus communis)
- Celosia or cockscomb (Celosia spp.)
- Chervil (Anthriscus cerefolium)
- China aster (Callistephus chinensis)
- Clarkia (Clarkia unguiculata, syn. C. elegans)
- Climbing snapdragon (Asarina, Lophospermum and Maurandya)
- Corn or maize (Zea mays)
- Cucumber (Cucumis sativus)
- Cup & saucer vine (Cobaea scandens)
- Cypress vine (Ipomoea quamoclit and others)
- Dill (Anethum graveolens)
- Dwarf morning glory (Convolvulus tricolor)
- Eggplant or aubergine (Solanum melongena)
- Everlasting (Xerochrysum bracteatum, syn. Helichrysum bracteatum)
- Fennel (Foeniculum vulgare)
- Flax (Linum spp.)
- Four O’Clock (Mirabilis jalapa)
- Gerbera (Gerbera spp.)
- Globeflower (Gomphrena globosa)
- Godetia (Clarkia amoena, formerly Godetia amoena)
- Heuchera (Heuchera spp.)
- Hollyhock (Alcea spp.)
- Job’s tears (Coix lacryma-jobi)
- Kniphofia, torch lily or tritome (Kniphofia spp.)
- Larkspur (Consolida spp.)
- Lavatera or tree mallow (Lavatera spp.)
- Lisianthus (Eustoma grandiflora)
- Lovage (Levisticum officinale)
- Love-in-a-mist (Nigella damascena)
- Lupin (Lupinus spp.)
- Malope or mallow-wort (Malope trifida)
- Melon (Cucumis spp.)
- Mexican poppy (Argemone spp.)
- Mignonette (Reseda odorata)
- Milkweed (Asclepias spp.)
- Moonflower (Ipomoea alba)
- Morning glory (Ipomoea spp.)
- Nasturtium (Tropaeolum spp.)
- Nemophila or baby blue eyes (Nemophila spp.)
- Nolana (Nolana paradoxa and N. humifusa)
- Painted tongue (Salpiglossis sinuata)
- Pea (Pisum sativum)
- Peanut (Arachis hypogaea)
- Pepper (Capsicum annuum)
- Perennial pea (Lathyrus latifolius)
- Perilla (Perilla frutescens)
- Persil (Petroselinum crispum)
- Poppy, annual species (Papaver spp.)
- Portulaca or moss rose (Portulaca spp.)
- Pumpkin (Cucurbita pepo)
- Quaking grass (Briza maxima)
- Rodgersia (Rodgersia spp.)
- Squash (Cucurbita spp.)
- Statice (Limonium sinuatum)
- Summer savory (Satureja hortensis)
- Sunflower (Helianthus annuus)
- Sweet pea (Lathyrus odoratus)
- Toad lily (Tricyrtis spp.)
- Tulip poppy (Hunnemannia fumariifolia)
- Watermelon (Citrullus lanatus)
- Zinnia (Zinnia spp.)
- Zucchini or courgette (Cucurbita pepo)