Try bark and sand, with slow release fertilizer. Bark doesn't need to be composted, probably better for not being pre-decomposed as it often tends to break down and turn mucky quicker than might be desired anyway.

For convenience and reproducibility, using a commercially produced mix (ie, Promix or Sunshine brands) has a lot of advantages. And if you buy it wholesale in the big bales, the price is decent even for a small grower.

It seems like your wish to mix your own might be based on a desire to avoid peat? Have you had enough experience with coir to feel comfortable with it? I could not get it to do what I wanted, and finally stopped using it.

You could also post this question in the Market Gardener Forum.

Hi, Drmedica!

"Am I silly to want to mix my own?"

Absolutely NOT. You get a standing ovation from me for just thinking about it. WHAT you grow in is really not very important - honest. You can grow plants in almost any media (w/o toxins or pathogens, of course) that will provide anchorage and air. It's really only important that the soil holds water and nutrients for your convenience - you won't want to water every 10 minutes, so it's convenient if the soil holds some water. Please don't discount what I just said. We know that hydro-culture and hydroponics are soilless methods of growing.

When you build your soil, think of air first. You can adjust every other cultural requirement easily. Water, sun, and nutrients are a snap to change, but aeration is not. If your plants are to grow as close as possible to their potential genetic vigor, you must insure that the soil you use remains well aerated for the life of the planting. Soggy soil = sullen plants. If you're profit-minded, you might wish to use one soil for quick turning plants, another for plants that will grow for a year before they are ready to sell, and still another for plantings you will have on hand for a longer period.

I have promised myself I will learn the advantages/disadvantages of growing in coir, but as yet, I have not. I use large volumes of soil and the expense is prohibitive. I am also very happy with the mediums I make with pine bark as the primary organic component. Pine bark is rich in a lipid called suberin that helps prevent micro-organisms from cleaving the hydrocarbon chains it is made of. In other words, it breaks down slowly & retains it's shape - and shape is important to aeration - is important to root health - is important to healthy, vital plants - is important to the "bottom line". ;o)

The pine or conifer bark is worth looking for. Given where you live, you'll need to be sure the logs it came from weren't ponded in salt water. Fir bark is even better if it's available. If you can find it partially composted, all the better - if not, uncomposted will work, but will require frequent N applications.

Here is a basic mix you can add and subtract from to fit your exact needs:

5 parts pine bark
1-2 parts sphagnum peat
1-2 parts perlite or 1/8 - 1/4 inch pumice
garden lime
slow release fertilizer
micro-nutrient source (powder/frit/seaweed emulsion/Earthjuice

For other readers, this is a superb mix for garden container plantings, too (and half the price of bagged soils).

Avoid using any sand unless the particulates are large, around BB size - more like small gravel. Yes, sand can help drainage, but it clogs micro-pores & reduces aeration. The same goes for compost. It provides nearly nothing in actual nutrient value & the small particulate size also clogs pores & causes soil to retain extra water.

The commercial mixes you can buy vary widely in quality. I would consider them for fast turning plants & keep an eye on drainage/aeration to see if they need amending with perlite or another drainage enhancer (pumice, perhaps), or just build your own.

I don't usually hang out on this forum, but a friend (who I admire for her ability to provide consistently reliable info) thought I might be able to help. I'll try to remember to ck back here, in case you have questions to ask of me. I wish you the best of luck. ;o)

Al

When I worked on a rhododendron and azalea farm they potted into pure bark, still fresh and steaming. Granular/pelleted fertilizer was used in combination with fertilizer in the irrigation water.

A friend uses bark and sand to grow a variety of plants for his mailorder/specialty nursery, varying the proportions with the type of plant. The sand is incorporated to provide a mineral component. Pelleted fertilizer and micronutrients are mixed in. Lately he's also been using corn gluten for weed control.

Due to the tendency I already mentioned for even comparatively coarse material like bark to break down rather rapidly and become poorly aerated, I would be wary of materials (like peat) that are already partly decomposed.

Thank you all for your info, and Al for the very detailed info and encouragement to mix my own. I'd been told by one of the local suppliers of mixes that I couldn't use raw bark, just composted so I'd been stumped. Thanks - Donna

Most welcome, Donna.

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Bark actually breaks down very slowly in containers, making it an ideal choice as the primary organic component. Aeration is always the first consideration in every soil I build, and conifer bark fits requirements nicely. A mineral component is not necessary in container soils unless ballast is needed to prevent toppling. As noted, sand, unless it is almost BB size or larger, is added at the expense of aeration. On the other hand, an organic component is not necessary in container soils either. There are few plants that could not be happy growing in 100% Turface, a hi-fired (almost ceramic) clay granule.

Raw bark is fine. Let the pile sit and cool for awhile if concerned about burning transplants. My point is that if you start out with a finer material like peat it has what may be undesirable textural characteristics right at the beginning, before there has been any decomposition. Likewise, the mulch type bark that I see being used for potting of hardy plants here has bark dust in it that will make it less well aerated than the washed(?) bark used for orchids.

Major commercial grower Monrovia nursery (see monrovia.com) has gone to using some sort of sandy soil as a major component in their mixes, I've seen it in their products (plants sold here) and heard it mentioned in conversation but have not read any details.

I'm not sure what you're getting at? I agree that peat does not compare to conifer bark in its ability to retain structure in soils. The object is to strike the best medium between water retention and drainage while insuring that aeration is not compromised for the intended life of the planting. You can usually use up to 15% peat in bark soils with no compromise as the peat, in small %, washes from the soil as it breaks down. Container soils are also about timing. Often, as the soil ages & decomposes, drainage issues are not as large a problem as you might thing. When roots fully colonize the container, water is used faster & each time you water, a fresh flush of air is brought into the soil. Roots also become a part of the actual soil structure and can promote the return of macro-pores in an aging soil.

Al

I am just visiting this forum....
Al; I am not in disagreement with your initial concern with regards to avoiding septic media conditions, however your first post hints at other factors:"...adding or subtracting (components) to fit your exact needs..." What is implicit in this forum is that production growers factor in and make an attempt to match/and work with: container size; specific plants they grow at different stages of development; media porosity (per cultivar modifications/container size); irrigation methods; specific fertilizers (any variation per plant group/stage of development/water characteristics); environmental factors they are operating under x turnover time...

I'm not sure if that's a nice way of saying, "Unless you're a production grower ..."?

The "adding subtracting (components)" comment was in recognition of the probable need to modify this basic recipe to suit plant material and cultural variables. While it is true that each variable you list might have sway in the pursuit of an "ideal" soil, it is also a probability that introducing these variables via a list of questions might well have confused or frustrated Donna.

Al

Hi 'Guys', its Donna again. I appreciate the input from everyone and want to make sure everyone plays nice. I know my quest to make my own soil mix is probably pretty adventuresome - I've heard speakers from production nurseries tell of using the wildest variety of materials - seems some will try anything once. As I've been discovering in my education, alot of things in growing plants are variable - for example in texts on propagation I'd read this worked sometimes and this worked other times - so many things are not SURE things.... But I like that you're all giving your opinion and sharing your experience - I can learn from it all.

I too often mix my own soil using compost, pine bark, etc. There's no question in my mind that a person can make a good mix that meets their needs. The point I was making, that may have been missed, is that when you are trying to start a business, eliminating variability and saving time can work in your favor.

You need time to develop a recipe and make sure it works for you before potting up plants, selling them, and having the customers come back and complain that they didn't do well.

If you go with the tested recipes that people provided, it still takes extra time to mix up potting material (as opposed to opening a bag), and you have to be sure that all ingredients are readily available. You need to set up an area to stockpile ingredients, a mixing area, and a place to store the mixed soil.

Depend on what scale you're starting out at, you may have time to figure these things out as you go along, and it sounds like you won't lose your shirt. But growing for market is sure different from gardening...

It is of my opinion, Donna, that we are lacking important information with regards to your operating conditions : do you have a heated greenhouse; what plants and what container sizes are you working with and are you growing from seed and/or plugs???These are only a few of the crucial factors along with noting Ann's comments pertaining to reproducibility which will influence your media selections... I see that you have an interest in Native Plants... do you utilize that journal site (for example) and hobnob with native plant professional growers?

Hi, its Donna again, sorry not to answer but I was out of town. I agree, I've got to suit my media to my plant material but that's true whether I mix my own or buy something since the bulk suppliers that are recommended here have lots of mixes. I am most interested in northwest shade natives and ferns and have had some success with ferns from spores but realize I'll probably need to buy plugs for any reliable plant material. I'm fence sitting because I'm not sure if the type of plants I WANT to grow are going to be what SELLS well. But lets say I do plugs, tho I also do cuttings, at least as a learning and enjoyment thing. I think until I settle on something more specific and in higher volume than what I'm starting with, I've got to do a general mix if there is such a thing, and finer tune it when I specialize.

Hi
I'm late coming to this thread, but find it fascinating. Bboy, can you give us any information about how your friend uses corn gluten?
We have available to us a ready supply of compost (leaf mold) and composted bark. Any suggestions about what I should use for aeration? Both vermiculite and perlite are readily available, but rather expensive. Weight of the pots is also a consideration, though.