Container Soils: Water Movement and Retention II

jeanette, Your photo is just fine, and your peony looks very happy. I bought a couple more bags of the small mulch as used the first one up, and knowing how Wal Mart doesn't reorder is things run out i elected not to take a chance on not getting it if I needed it.

Donna

Well, that is pretty small bark, so I think I just might mix it with the first bag I bought of the larger stuff. My daughter bought some Coir bark off of ebay and is sending me a brick of it to see what it is like. It looks like midway between my 2 bags which is what I think I would like. It definitly is more expensive than the bark mulch from WalMart. And a little more expensive than the other bark I bought.

Jeanette

has anyone used composted cotton burrs in their mixes?

High in cellulose - breaks down quickly.

Al

Just saw a big stack of bagged cotton burr compost when I visited Guy Robbins' nursery in Martin TN. He is a reknowned horticulturist and ex director of the Memphis Botanic Gardens. Anyway he highly recommends it so I am keeping an eye out for some to use in my container mix and as a soil conditioner in the gardens.

carol

Great in the garden, high in N, breaks down too quickly for me to want to use it in containers when there are soo many other more suitable ingredients that will perform the same function. I'm sure it's fine in the short term, as in quick rotation greenhouse plant material, though. I wish you good luck in your growing endeavors - no matter what your choices.

Al

Al I came into a free windfall on some vermiculite and per-lite used in pool construction. Trouble is that it is very fine. Therefore it will hold more water. I want to use it both for raised garden and containers. Will it impede the draining of the mixtures.

This message was edited May 24, 2007 8:25 PM

I'm not sure if all vermiculite and perlite are created equal. Years back, I bought a 4 cu ft. bag of perlite from a masonry supply house, only to learn it was treated with silicone water repellent. I was too leery of it to use, so I discarded it. I can't really answer your question, but I would experiment before jumping in with both feet. I don't think I would use the vermiculite in containers though. Like Cotton burr compost (above) it collapses quickly in containers and holds too much water when included in any quantity - except in very short-term plantings or some specialty soils.

Al

A lot of the seed catalogs are selling the real fine vermiculite for starting seeds to keep the plants from damping off.

Jeanette

Really? is vermiculite for moisture retention? I used it once, not knowing what it was in my early garden days...

Vermiculite is an aid to moisture retention, and provides good aeration temporarily. It does break down structurally and compact quickly though. Damping off is a fungal disease. Vermiculite is not prophylactically active in actually preventing damping off. It is effective simply because it's sterile and doesn't harbor disease spores (at least in large numbers). Perlite, or a mix of perlite and vermiculite would be my choice before using vermiculite as a stand-alone seed starter.

Al

Thanks,
that was pretty much my understanding.
Rj

No, it was not to start the seeds in. You sprinkle it on the top VERY lightly after planting the seeds in your regular starting mix to keep the moisture in but the top of the vermiculite dries out around the stems of the plants and that keeps them from damping off.

Guess you have to use your imagination guys. LOL

Jeanette

Bumping this continuation of the "other" thread, since it's still getting all of the attention. =P

I am using coarse crushed oyster shells instead of Vermiculite. A 50# bag of the crushed shells cost about $8, whereas vermiculite is up to $10 for just a small bag. Turkey grit is also "cheep" (I am sooo funny) but it's really heavy, and for some reason, smelly when wet. I use a local farmers co-op/feed store for these.

Is this OK? My plants seem to like it.

For those of you having trouble finding pine bark fines, try a retailer that supplies landscapers- esp. the high-end ones. I found "Southland Pine Bark Mini Nuggets", which seem to fit the bill just "fine" :-). For anyone in Eastern MA or NH it's available at Corliss Bros. in Ipswich, MA. (GREAT people!)

I've also added water crystals to the mix; sometimes my days run away with me and I can't water.

I've passed the recipe along to non- DG'ers (I think they've joined up now!). One of them uses her compost tumbler for mixing big batches ot the soil! Great idea- I may go that route as well.

-Melissa

Good ideas!

I'll throw my 2 cents worth in on polymers. They work, as long as we remember what their real function is. They are meant to hold water for the benefit of the plant, not the media. Most polymers, probably all of them, have a much higher absorbtive level than the surrounding media, and they are not prone to readily giving up their moisture to that media. Plant roots will grow to and through them, and will take up the absorbed water. However, your media must remain moist in order to remain healthy and to provide channels for root growth and air. How many times have you heard people talk about using polymers for water management only to complain later that their media has become like a rock? That's because the polymer is competing for limited water and winning. We need to make sure the media is regularly watered for its own sake. The polymer will keep the plant alive for awhile longer if water is the issue, but the plant is just at much at risk if the media isn't healthy. For that, you need a regular routine of watering.

Been using polymers for years and never once had that problem. I water less frequently than I would otherwise have to, but when I do water I water the same way as I do without crystals. I make sure the entire thing is dripping. It's better to mix the crystals throughout the media. Some people just put in the 'hole' where the plant is going, along with some time release fertilizer.

It's probably because you're watering enough to do the trick for both the plants and the media, but are using the plants as a "barometer" of when watering is needed. If you're using a time relase fertilizer, it's a good idea to run the water through until it's running out of the bottom of the pot, in order to flush out the accumulated salts. Also, you're correct to mix the crystals throughout the media. Putting them in the hole could result in root rot from too much water in the immediate root zone. The same for time release fertilizer. Since the release rate for time release fertilizers is generally dependent upon soil temperature (generally about 70 degrees), it's important not to have the fertilizer too close to the roots. When soil temps get to over 100 degrees, which they will in most any zone on a sunny day, the release rate can become as much as 40 times faster, which could result in root burn.

All good points! Been doing just that. The flushing is very important for the self-watering pots too.

Victor: Check your DMail

Two unrelated questions for Al or anyone:

First, I have know people who deliberately stop watering before the water drips out the bottom of the pot. The idea is that the medium gets (admittedly variably) wet, yet the perched water table doesn't accumulate every time you water. Now, assuming that periodically you flush the container to prevent salt buildup, and putting aside the difficulties in judging exactly how much water to use, is there any reason not to water in this fashion?

Second, what are the micro- and ultramicroporosity of Turface or kitty litter?

SB

Hello, R. This isn't anything you don't already know, but usually, anyone that waters in this manner is making an effort to stave off root rot issues in a poorly aerated soil, but I suppose this type of watering would trump copious watering if root issues appear probable. If this is the case, it begs the question of how can you then flush the soil w/o risking root issues? You also have the possibility of root death in isolated parts of the container and/or the probability that fewer nutrients would be available because the soil would not be evenly moist, even dry in some parts of the container. Last, as you mention, if the person is reluctant to flush the soil on a regular basis, carbonate and fertilizer salt build-up is inevitable.

Don't have the info on ultramicroporosity, but am wondering why you're curious? Turface has about 40-50% inter-aggregate (mostly) microporosity and an additional 30-40% intra-aggregate (mostly) macroporosity for a whopping 70-85% total porosity. There is approximately 13 acres of surface area in one pound of Turface. As long as it is fired at sufficiently high temperatures so it remains stable, kitty litter should very close in stats.

Al

In that case I'm gonna get me a pound of Turface and I'll finally have the acreage I've always longed for! Now what am I going to plant on it???

I ask the question because I understand that the ultramicropores hold water unavailable to plants. I wondered if the ultramicroporosity in Turface was higher than other media components such as bark, CHC, or perlite.

In other words, Turface holds lots of water, but does it hold water in such a way that it is readily available, or rather does some of the porosity relate to water that the plant cannot reach?

Much lower than almost anything except sand or rockwool, which are close. Pine bark holds about 90% water by volume when fully saturated and retains 30% of its water at the point where it becomes too tightly held for plant uptake. The moisture retention curve of peat is approximately a mirror image of pine bark. Coir holds about 94% water at saturation and water becomes unavailable when there is still about 38% remaining. Perlite holds 63% water by volume and retains 24% when water is unavailable to plants. Turface MVP (from the bag) holds approximately 75% water by volume at saturation and has only about 3% remaining when water is held too tightly for plant uptake.

That what you needed? ;o)

Al

Al, any opinion on crushed oyster shells as an inexpensive additive?

Yes! That's great, Al, thank you.

Jax4 - often it's not so much what we use in soils, but the physical characteristics of what we use that is important. In the case of oyster shell, there are both physical and chemical considerations. The volume of components is also frequently important. We can take several perfectly good soil components that can stand alone as a good choice for soils, but when we combine them, we can have a whole that is not equal to the sum of the parts in its utility.

Crushed oyster shell will slowly raise soil pH, which is of special concern if your irrigation water is high in carbonates. Another consideration is the size and uniformity of the particulates. Ca supplementation is usually needed in most container soils. In oyster shell, you'll find mainly calcium carbonate, but small quantities of calcium phosphate and magnesium carbonate are also available.

You didn't mention if you were adding small quantities as a nutrient source or using them as an actual primary structural component of the soil. I'd need to know the answer to that before I could answer your question, as well as what you're growing & some idea of how hard your water is. I'm guessing though, that you already have enough info here to sift through for your answer. Rinse thoroughly before using to leach salt from the shells if you decide to use them.

Al

OOPS on the rinsing part...

I've been adding about 1/2 part oystershells to replace the vermiculite in your recipe, due to the high $ of vermiculite. I'm including turkey grit to round out the vermiculite portion (very coarse crushed granite). In my last batch, I used a brand-name "soil conditioner". It looked suspiciously like the 10 cent per lb grit! I have been using crushed shells for ages to foil slugs, so I always have plenty on hand. I think the wild birds thank me, too.

OOPS - there is no vermiculite in any of the mixes I use. ;o) Perlite perhaps?

Al

Al,

I've been following this thread with interest.

1. The most recent issue of Container Gardening (from BHG) says to invert a plastic pot, raised slightly on pot shards, inside containers to reduce the weight and expense of potting medium. Would that work? I've used sealed plastic soda bottles. As long as there is a top to bottom column of soil, wouldn't that "trick" the water into thinking evrything was AOK? Weight is a big concern for us.

2. Are we talking about media for potting annuals? So it really has to last just one season?

3. Al, can we see some pictures of your containers?

xx, Carrie

Al,

Thanks for all of the information on container gardening. I just purchased pine bark fines at Ken Mulch in Louisville, Ky. He said all the nurserymen use it. I am going to try and repot some of my containers this weekend. I am wondering if this will also work for hanging plants. I now use Miracle Gro Potting soil and am thinking with the pine bark fines, the containers may be too heavy for hanging.

BettyFB

They'll likely be lighter, Betty, but they'll likely need watering more frequently, too.

R - I also think the study tends to support or illustrate what I was saying. .... something like adding a pint of BBs and a pint of sand to a quart of marbles & still ending up with a quart of material.

Al

Al,

Thanks for the reply. I plan to take some time and read all of the information this weekend. To me it is very exciting. Watering more will not be a problem for me ,as I am the type that probably waters too much anyway.

BettyFB

Al, my poultry grit and shells are to replace the perlite. I have a personal dislike for perlite; the white balls look distracting and unnatural, but that's me :o)

I have been experimenting with brands of pine bark fines, peat (Miracle-Gro now makes a special super peat moss that is 10x more expensive that the regular stuff, probably b/c it has "Miracle-Gro" stamped on the package.)

I have to perfect this mix for the BIG potting season- hauling in the house plants and other annuals for the winter, after a summer in the sun.

Thank you for all of your information (my plants thank you, too!). I have always wanted to grow hybrid tea roses, but deer munching and root incursion from other garden plants always ruined them. Your basic soil recipe seems perfect for large pots for rose bushes! I'm trying that next!
-Melissa

Hi Al,

Here is a picture of a container I made last week using your formula. I will keep you posted how well it does. I would like to see pictures of your plants in containers for ideas and to see how great they look!!!!

Looks great Betty! How often do you water?

I am watering daily just like I water all the plants. I will post another picture of it in a few weeks to show how it is doing with the the pine bark fines container soil.