A Discussion about Houseplant Soils (long post)

What kind of ratio would you use for a christmas cactus or sansevieria?

1:1:1 by volume

1 part uncomposted pine or fir bark
1 part screened Turface
1 part crushed granite (grower size grit) or #2 cherrystone
gypsum

Al

What does diluted hydrogen peroxide do to soil/plant? Are there any subs for gypsum? I have drywall scraps, but not sure if it's gypsum or other, lol. I can't get to town for a few days, but will just wait if no reasonable substitute.

H2O2 has an extra O atom (compared to H2O) in an unstable arrangement. It's the extra atom that makes it useful in horticultural applications. Generally, we're not concerned with aerobic forms of bacteria normally occurring in container media or on roots.
Since H2O2 is an unstable molecule, it breaks down easily. When it does, a single O- atom and a molecule of water is released. This O- atom is extremely reactive and will quickly attach itself to either another O- atom forming stable O2, or attack the nearest organic molecule.

Reduced O levels and high temperatures encourage both anaerobic bacteria and fungi. Many disease causing organisms and spores are killed by O, and the free O- H2O2 releases is very effective at this. Additionally, when plants growing in water-retentive media are treated with H2O2 it will break down and release O into the area around the roots. This helps stop the O from being depleted in the water filled air soil air spaces until air can get back into them. High O levels at the roots will encourage rapid healthy root growth and discourage unwanted bacteria/fungi.
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I know H2O2 comes in several different strengths, the most common of which are 3% and 35% solutions. Least expensive is the 35% product which you dilute (to an approximate 3% solution) by mixing 1:11 with water. I have used the 3% solution at 1-½ to 2 tbsp per gallon as a cutting dip/soak, and have mixed it into irrigation water for plants in extremely water retentive soils at up to 3 tbsp per gallon, both with good results and nothing adverse apparent.

H2O2 in high concentration is a powerful oxidant and quickly oxidizes almost anything it contacts, so be careful with it if you use it. A solution that is too strong can destroy any organic molecule it contacts.

I’ve seen this chart posted several times as suggested strength solutions for use in watering plants. You may wish to start at a lower concentration , such as I’ve used, and experiment.

TO THIS AMOUNT OF WATER ADD THIS AMOUNT OF 3% HYDROGEN PEROXIDE --OR-- ADD THIS AMOUNT OF 35% HYDROGEN PEROXIDE

1 cup, add 1-1/2 teaspoons … 35% - 7 to 10 drops
1 quart, add 2 tablespoons … 35% - 1/2 teaspoon
1 gallon, add 1/2 cup … 35% - 2 teaspoons
5 gallons, add 2-1/2 cups … 35% - 3 tablespoons plus 1 teaspoon
10 gallons, add 5 cups … 35% - 6 tablespoons plus 2 teaspoons
20 gallons, add 10 cups … 35% - 3/4 cup plus 1 tablespoon plus 1 teaspoon

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Gypsum (CaSO4) is a unique compound of Ca(cium) and S(ulfur), so there is no real substitute for it, per se. If we consider it only as a source of Ca, then there are other products that will supply the Ca, but most will raise soil pH. Gypsum is suggested for the gritty soil mix because it (the gritty mix) starts out at a higher pH than the 5:1:1 mix and gypsum has little or no practical effect on media pH. Dolomitic (garden) lime is suggested as a source of Ca and Mg for the 5:1:1 mix and to raise its pH to a more favorable level.

Drywall has binders and other materials other than gypsum in it, so I wouldn't trust it as a source of plant nutrients.

Al

Thank you, thank you, thank you. As always, you've helped me understand what I needed to know and I appreciate that very much. It was recommended for fungus gnat larvae, but I see that it can be more beneficial than that :).

I guess I can find gypsum at a farm store, since I didn't notice it at Lowe's.

When you've change soils, you will have put the gnat issue behind you.

Just D-mail me your addy & I'll send you some gypsum. I doubt I'll miss a little from a 50 lb bag. ;o)

Al

Al, I've been re-reading this thread, which led me on a search for Turface, which I was unable to find in the UK. You previously suggested Montmorillonite as a possible alternative but how about cat litter instead? I came across a site on Bonsai growing which recommends certain types of cat litter for use in soil mixing. The author of the website seems very enthusiastic about it, but I would be very interested to have your opinion also. Here is a link to the page: http://www.bonsai4me.com/Basics/Basicscatlitter.htm

All cat litter is not created equal. Some is fired at low temperatures and breaks down structurally when it becomes wet. Some have perfumes and clumping agents, but some work very well. I would look for a product that is appropriate in size (particles concentrated in the 1/8" size range) with no perfumes. I would then freeze it solid in water and then thaw. If it remains stable after freezing, it's a suitable substitute for Turface.

You might also look in the direction of calcined diatomaceous earth. In the US it's sold as a floor-dry or oil-dry product. NAPA stores sell it (part #1822, I think) here & it is a suitable substitute for Turface. I screen these products through insect screen & use the coarse fraction in soils and the fine fraction in hypertufa or spread on the gardens/beds.

Al

Thanks for the quick reply, Al. You make the same points as the Bonsai article regarding the stability of the granules and how to test them. Think I'll give it a go. Thanks again.

Paul

I didn't even bother to look. ;o)

Al

Hello Al, I am a newbie who is very impressed with your info about soil. It explains something I have been worried about with my Boston ferns, namely that they seem waterlogged at the bottom, no matter how often or not I water. I have been in such a quandry about how to water, but I believe now, that it is the soil mix that is causing the problem. Thanks for taking the time to help out.

I have another question that I thought you might be able to help me with, soil testing. This doesn't pertain to containers, but it is soil science. I want to test my garden soil in several spots and the local extension service is too expensive for me to do multiples. I have heard that the probe meter things are not very helpful as they are inaccurate. Is this true? And is it possible to get accurate (enough) results from the little chem lab kits to be able to accurately meet the needs of the soil?
Erin

Hi, Erin. Thank you for your kind words. First, let me say that if you push a wick up through the drain hole, it will help to drain some of the perched water you're witnessing at the container bottom. Undoubtedly, your plants would be much happier if you could eliminate that water through wicking or through a change to a more open soil, either/both of which would help to eliminate some of the effects of the cyclic death/regeneration of roots caused by the anaerobic conditions.

Other ways to eliminate excess water from containers:

A) Tilt the container at a 45* angle until it stops draining. See how effective this is by allowing a container to drain in a normal position after a thorough watering. Simply tilting the container will cause a considerable amount of additional water to drain. I can explain how this works if you're curious.

B) Hold the saturated container at chin height over a sink/tub, etc, lower it to waist height at a comfortable speed and then lift it immediately and rapidly back to chin height. You take advantage of the inertia of motion to drain excess water by this repeated maneuver.

C) Hold the container by the rim at arm's length. Spin in a half circle (mostly for outdoor stuff) or even a full circle. (For gosh sake, don't make yourself sick or dizzy) ;o) The centrifugal force will remove water from the pot in the same way a washing machine spin cycle works.

I'm going to suggest you post your (garden) soil question on the soil forum, where you'll get different perspectives. If you're talking about moisture/pH meters you often see available at plant shops, you're correct, they are very inaccurate; and my first inclination is to think that you won't get enough info from the do-it-yourself kits, but I would defer to those with more experience in that area.

If you wish, and if you let me know, I'll watch the post and let you know via Dmail which replies I would tend to value most.

Al

Al, thank you very much for the options, which I will employ as I am trying to gather the supplies for your recommended potting mix. I am curious about why the angle tip works, if you have the time..., by the way thank you for such a quick reply I will go ahead and post the other question on the other forum
Thanks,
Erin

Why tilting a container causes more water to drain:

First, it only works if you're using a soil that supports a perched water table (PWT). (More here: http://davesgarden.com/community/forums/t/719569/ ) Now, imagine that you are looking at a cylindrical pot. The side view of the cylinder (in two dimensions, width & height) looks like a rectangle. Perched water tables are a constant height in a soil, no matter what size or shape container you put the soil in. If a soil supports a 3" PWT, the PWT will be 3" in a 3" deep container, and 3" in a 30' deep container. Shape has no bearing on the height of the PWT, but it does have a bearing on the VOLUME of water in the PWT.

I do this experiment when I give talks on container gardening or soils: Saturate a sponge. Hold it so the longest dimension is vertical and the shortest dimension horizontal - like a cracker box on end. If you wait until it stops draining, then hold it by a corner, a considerable amount of additional water will drain from the sponge.

Here's why: If you draw a line through a 6" wide rectangle, 3" above the base to represent the ht of the PWT, then tilt that rectangle 45*, what happens? The level of the PWT becomes the BASE of an inverted triangle, with the apex being the lowest point. We know that the surface area of a triangle with a 6" base & 3" height is much less than a rectangle with the same dimensions. The VOLUME of 3-D figures is much less as well. Since there is much less soil in the volume of the container that is capable of holding perched water, the o/a volume of perched water is much less, even though the ht of the PWT remains constant.

I have pine and juniper bonsai that do not tolerate a PWT well, so during periods of prolonged rain, I prop the containers up - 2x4s on edge under one side to passively reduce the volume of water in the PWT. When it stops raining, I remove the blocks - works like a charm, and you can do the same thing after you water your houseplants by simply tilting them until they stop draining. Try it - it will help.

Al

Hi Al, GREAT to see you here....just a quick comment about the earlier post about kitty litter. I have been using it for about a year (unperfumed) in my gritty mix, and can't understand why, when I repot plants the mix is thick and sticky from the clay, yet the plants are thriving! Is this because of minerals in the clay? I've heard that clay deprives plants of oxygen, is this true? Thanks for the tip about freezing the granules first, I will do this ASAP before my next repotting. WOuld love to find TUrface somewhere in a reasonably sized bag, but have not had much luck. Just renewed my membership here in order to continue to benefit from your knowledge and experience!

Eileen

Lol - so you followed me, huh? That's nice to know ..... and VERY kind of you to say so. Thank you very much.

Almost assuredly you're sacrificing vitality because of reduced aeration. I would really encourage you to try to find Turface or even calcined diatomaceous earth. NAPA auto parts stores sell calcined DE in nice size bags that don't weigh much more than 25 lbs, and it's not very expensive. It's unlikely you'll find Turface in anything other than 50 lb bags at a rate a reasonable person would be willing to pay - but maybe not a reasonable desperate person. ;o) You should screen either Turface or the DE through insect screen or through a "regular" size mesh kitchen strainer before using the larger particle fraction. This helps with aeration and to eliminate any perched water. Good luck, Eileen.

Al

Thanks Al, I think I will try for the DE - my husband used it when we had our fish tanks, tho I will be sure this is the "right type" ( if there is such a thing!) of DE when I ask at the petstore where we used to buy it. Looking forward to many more of your wonderful posts here!

Eileen

I've been reading through this post and was planning to try this out. Then I got to where gnats were mentioned and that alone would have convinced me to try it! I just have a few questions.

I thought I read you adjust the mix for the type of plant, did you? If so I've read spider plants like moist but well drained and not soggy water, would I had a little more grit to the mix to achieve that?

Also, I'm home most of the time and rarely leave for longer than the daylight hours but once a year we go on a 4-5 day trip. I'm assuming those "globes" and "spikes" used to water while you're away wouldn't work with this type of soil, is this correct? Having people come in is nearly impossible but if there's a set up I can MacGyver up I'd be thrilled.

This last one is sort of OT, I apologize, but how do you keep your soil coming out the drainage holes? I'm not fond of saucers for my hanging baskets but I also don't want the stuff falling on the floor. I've had pantyhose, onion/garlic bags and even window screen suggested.

I thought I read you adjust the mix for the type of plant, did you? This is the same soil I use for my bonsai trees, and I DO alter it to suit different tree species. For instance, I use 3 granite:1 bark:1 turface for pines and junipers because they don't like much moisture in the soil, but for houseplants, succulents, and cacti, I use the basic 1:1:1 ratio. If so I've read spider plants like moist but well drained and not soggy water (soil), would I had a little more grit to the mix to achieve that? There is no need to tinker with it for houseplants, unless you're growing them outdoors for the summer in very hot/windy conditions.

".... once a year we go on a 4-5 day trip ...." It won't hurt anything if you find some of your plants can't go the 4-5 days without watering, if you set them in a saucer of water that will provide just enough water to get them through the extra day or so required to get you through. The gritty mix holds almost no perched water, so it's not like you'll have the several inches of saturated soil at the bottom of the container like you would with heavier soils.

I use squares of insect screen or plastic canvas, http://bagntell.files.wordpress.com/2009/12/pcanvas2.jpg like you'll find at hobby stores dirt cheap.

Al

We are having a hard time finding grit or granite chips and pool sand (that is not in a filter), is there something else I can use in it's place?

If you can find pumice/lava rock in a favorable size (3/32 - 3/16), try

4 pumice
3 bark
2 Turface

Al

Out of curiosity would black or red lava rock work in this mix? I saw it somewhere for a decent price but I wasn't sure if it would be acceptable.

I also got confused somewhere, I thought pumice was a substitute for Turface. I think though I will try to find a source for it locally, although ordering it online might have to work since I'm limited transportation.

The fir bark on this page, http://www.orchidmix.com/cat2.htm
Would fine bark be my goal?

For the bark, the fine is a little too fine, but the next size larger is a little too large, so I suppose you could buy a little of each. 1/8 - 1/4 is ideal. I buy it in 3 cu ft bags from an orchid grower's supplier for $15-17 per bag, depending on how much I buy. 20 bags nets me the $15 price.

The lava rock will work, as long as you remember that size is important to getting the most out of the mix. You want it to be right ion that 1/8" size range - not too much larger or smaller.

The pumice will be more water-retentive than granite, on a size for size basis, but not as water-retentive as the Turface, which is why I made an educated guess about how much of each to use if you can't find the granite. The granite is nice because by varying the amount of granite and Turface, which are at opposites as far as retention, you can adjust the water retention. When you use a product that is somewhere between Turface and granite, you lose some of the ability to adjust. It's not the end of the world, but it helps to illustrate that there was a lot of thought and experimenting involved with selecting the ingredients and a starting ratio for combining them to come up with the gritty mix.

Al

Could I substitute Coir for the peat in this recipe? I accidentally grabbed sphagnum moss and when I went back for the peat I spotted adult gnats crawling in the bag.

3 gallons pine bark (see picture above for appropriate size)
1/2 gallon peat (sphagnum peat please - no reed, sedge, or Michigan peat)
1/2 gallon perlite
small handful lime or gypsum (ask about this if you make this soil)
1/4 cup CRF (if the season is appropriate - ask if you're interested in an explanation)
1 tbsp micro-nutrient powder (or make sure the fertilizer you use contains the minor elements)

You can if you wish, but I've never had good luck with coir. I've done several side by side experiments with coir & CHCs vs peat and pine bark, and the coconut products have always come up short, but it's your call.

If you make that recipe & use coir, use 3 tbsp of lime. Actually, if you tell me where you found that recipe, I'll go back and edit it so the volume of the lime component is listed more accurately.

Al

At the top of this post.

I'm going to visit a nursery for everything. The bark I bought was too large so I'll see if they have both coir and peat there.