Gritty mixes, 511 and SWCs oh my! Newbie confusion

rayona(NYC)March 6, 2011

This is my first attempt gardening since my mom gave me pansies and a watering can twenty years ago. Between hunting down seeds, pots and "soil," I am thoroughly confused already.

After reading this forum I know not to use dirt or most commercial potting mixes. I'm planning on growing a few annual herbs and flowers, a couple of vegetables, tomatoes and maybe strawberries on the roof of my building. There is no access to water so I will be lugging buckets up a flight of stairs.

Should I keep it simple the first time out and stick with a commercial mix in standard pots while I learn about my growing space? Should I get fancy and build some SWC? Preliminary local sourcing of either mixes' components hasn't gone well--I can find peat and perlite but there isn't a big supply of gravel or bark in urban garden centers.

Thanks in advance,


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tapla (mid-MI z5b-6a)

Hi, Jess. Here's the honest perspective - You can grow healthy plants in commercially prepared soils or in commercially prepared soils that are further amended with peat and perlite.

By choosing a soil that has a primary fraction of larger particulates, like pine bark, you eliminate the all or most of the excess water that so often causes issues when you use out of the bag soils. The additional advantages that are of considerable importance are, you can water the soils that drain more freely to the point of flushing the soil w/o risking subjecting the roots to anaerobic (saturated soil) conditions that causes the cyclic death & regeneration of fine roots, which is costly in terms of lost potential because plants have to expend energy to replace these roots that would otherwise have gone to producing flowers/fruit/increased biomass. It's been argued that roots die all the time so it's no big deal. This really isn't a logical way to look at the picture. Anything we can do to minimize the number of roots dying on a regular basis is an increase in potential for the plant in growth/harvest/floral display that will actually be realized. Even though in situ plants see a regular death and regeneration of roots usually involving conditions related to moisture - that doesn't change the fact that it's still expensive for the plant to replace those roots, and anything we can do to mitigate losses is a decided plus. A very good analogy is the athlete that competes in a sport where injuries are likely to limit his/her career. We can say with certainty that the injury goes part and parcel with the chosen career, yet if you consider the degree to which we go in trying to mitigate needless injury (NASCAR, football, fencing, e.g), it might be easier to see the point.

The other decided advantage in using a soil based on bark rather than peat/compost/coir is the forgiveness factor. Free-draining and well-aerated soils provide a much broader margin for grower error in the depts of watering/fertilizing. This can be a very significant advantage for new and experienced growers alike.

There is no denying that a commercially prepared soil is very convenient - up and running in a matter of minutes with little fuss or muss. Regardless of what direction you choose, there will be plenty of help here that will help you squeeze the most out of your efforts.

Best luck.


    Bookmark   March 6, 2011 at 2:11PM
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Thank you for working on a Sunday! ;)

I had somehow missed previous discussions of Repti bark as a replacement for the pine bark fines, sifted. It seems like that could be a great solution, especially in Raybo's 3:2:1 SWC mix.

My herbs sprouted this weekend and I am really looking forward to the day when I can get them outside.


    Bookmark   March 6, 2011 at 4:52PM
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tapla (mid-MI z5b-6a)

Lol - cute! (....on a Sunday)

Hey, Jess. The fine reptibark and the PBFs are probably best suited to 2 different soils. The fine reptibark would work well as a fraction of the gritty mix, and PBFs would serve best as the main fraction of a soil with peat and perlite as its other significant compliments. Just wanted to make sure you were clear on the difference?


    Bookmark   March 6, 2011 at 9:23PM
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Well, now I am thoroughly stumped.

It was my understanding, after reading your fantastic posts about water movement in soil, that the basic goal of the potting mix is to have similarly sized materials that drain well and don't compact. So is the size of the particles different in the 511 vs the gritty mix? I thought it was all supposed to be 1/16-1/8 inch in size.

I did find a local hydroponics supplier and will visit them tomorrow.

Thank you again for all of your help.


    Bookmark   March 8, 2011 at 8:51AM
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tapla (mid-MI z5b-6a)

The 5:1:1 mix is a replacement for bagged soils that are too water-retentive to provide a healthy environment for roots. It is designed to provide much greater aeration and less water retention, and specifically, a PWT that is greatly reduced in ht. This is achieved not by adding pine bark and perlite to a peat-based soil, but by starting with a large fraction of larger particles (pine bark) and adding just enough peat and perlite to adjust the water retention to something more favorable (to roots) than the peat-based soils can offer. The particle size of the gritty mix needs to be more carefully controlled if it is to take the properties of drainage and aeration to ideal levels. The aim of the gritty mix is to provide superlative aeration and good water retention (you can always water more but you can't add aeration to a soil after it's made), but w/o supporting perched water. As noted, the fact that we're trying to eliminate perched water but still provide good water retention requires more attention to details than simpler soils like the 5:1:1 mix.


    Bookmark   March 8, 2011 at 3:11PM
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Hi, Jess!

If you're going to be using more than a few small pots, ZooMed ReptiBark might not be the most cost effective way to go for the fir bark portion of your medium mix... it's roughly $5 for 4 dry quarts, which isn't much when you need to fill a number of large containers. It's about $8 for a medium sized bag of ReptiBark, which is 10 dry quarts.

I use it for several reasons... it's convenient and available locally, no sifting or screening required, and I only need to make small batches of medium at a time. This spring, I'll need a lot more fir bark for the re-potting I intend to do, so I'll be heading north to Oak Hill Gardens, orchid growers, and buying their fine grade of fir bark in bulk. It's a 3 and a half hour drive, so I'll be stopping in next time we go north to visit the kids and grandkids.

For someone who needs a larger quantity of medium, I'd direct them to look at orchid growers/greenhouses, mulch companies, bonsai growers, etc... in fact, in many cases, Al or someone else here that lives in your general area might be able to direct you to the right place(s) to look.

It is my understanding that the 511 mix is generally used for short term plantings, like annuals or vegetables... and the gritty mix is used for longer term plantings, such as houseplants. The gritty mix contains a set of more durable ingredients, with the fir bark being the one item that will eventually break down. But a well made batch of gritty mix should be good for at least 2 years, and probably longer.

I plan to keep my bulbs in it for about 2-3 years. I figure that will be around the time I get to re-potting.

I will be using both mixes this year... I've heard such good things about the 511 mix that I'm really excited to give it a try! And I can already say that I adore the gritty mix! My bulbs and other plants couldn't be happier! :-)

    Bookmark   March 8, 2011 at 3:50PM
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Great thread and fantastic advice Jodi and Al!

Jes, to have a big bag the fine orchid bark shipped from you from "Tindra's Orchids" might not be too expensive. In fact, many times of the year they have free shipping if you order a certain amount from them. They are located here in Ma and you are only a state over.


    Bookmark   March 8, 2011 at 5:17PM
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Thank you both! There is so much to consider the first time out.

Apparently I found a great deal on the Repti Bark--$17 for 24 quarts and free shipping. That made it seem more reasonable than the mulches I was finding. I can get either fir or cypress for that price. The cypress bark looks smaller but more irregular. Thoughts about which one to go with? (Or a bark available through Amazon.) I'd like to make a batch this weekend so I have to pull the trigger tonight. :o

Here is a link that might be useful: Zoo Med cypress bark

    Bookmark   March 8, 2011 at 8:00PM
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tapla (mid-MI z5b-6a)

Please skip the cypress mulch. It was studied by Cornell university and found to be mildly allelopathic to many plants (when used as a mulch). Used as a significant fraction of a container soil, the allelopathic properties would be magnified considerably.


    Bookmark   March 8, 2011 at 10:01PM
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Yes... do stick with fir bark/pine bark.

And be aware that reports are coming in that the contents of the larger ReptiBark bags contain a fir bark product of larger particulate. I have not seen this first hand, but I've only purchased the small and medium sized bags of ZooMed ReptiBark from PetsMart and Meijer's, so I have no way of knowing for certain.

I don't know if it's a quality control issue, or if certain batches are larger than others at factory packaging time, or what the deal is... but I want you to be aware of this before you order anything.

It might be to your advantage to look closer at fir bark for orchid mixes in fine grade. Or... you could always order the ReptiBark in the smaller bags, but get two instead of one... for trial, that is.

    Bookmark   March 9, 2011 at 5:28AM
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redshirtcat(6a MO StL)

I don't mean to hijack this thread but it's about SWCs so I figure this is a decent place to ask:

Does the 5-1-1 have sufficient wicking capability to bottom water? I guess it must if people are using it in SWCs but I just want to make sure before I kill several flats of seedlings in the 5-1-1 with under watering.

Can I fill 1 flat with water and put in my 6-packs of seedlings in 5-1-1 and bottom water effectively or will there not be enough water uptake without more peat?


    Bookmark   March 9, 2011 at 7:14AM
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You guys are the best! I'm planning on buying my containers today and I'll be sure to look for orchid bark while I'm at it.

My plants are thanking you--I think they have been saved from at least three deaths already!


    Bookmark   March 9, 2011 at 9:41AM
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I used a modified 5-1-1, more like a 3-2-2, in my wicking containers. BUT, those needed to wick 10 inches; you may find that you can wick a couple of inches OK.

I'd try an experiment and put the mix in your containers, then wick. See if they stay damp. If it does, try some plants a couple weeks ahead of the others to make sure they do OK.

Others have wicked with versions of the mix; it's hard to find using the search, but the discussions are there.

    Bookmark   March 9, 2011 at 5:23PM
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