Best medium for moisture retention in hanging baskets and pots

piper101(Z 9b So.Calif)March 29, 2008

Hi, After taking a class from a local nursery about soils etc. I'm contemplating replacing my soil on most of my container perennials and hanging baskets etc. Now that I know the potting soil I used, bagged, was mostly junk, I'd like to get more life out of my perennials and this might be the way. I was thinking that it might help to have an agent in the soil that would hold moisture in my pots and hanging baskets since there are times when I am away from home and hire a young girl down the street to water etc. I usually end up losing a few for lack of water, I'm assuming.

So....when I do this, would perlite or vermiculite be the better water holder? Or something else someone knows about? I know about pumice for drainage and airation. I do the organic thing so I don't want to use those funky water crystal things. Thanks for your help.

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The problem is with containers they are exposed to the heat and sun nothing will stay moist for long but I believe compost would be the best medium to plant in versus perlite or vermiculite.

Here is a link that might be useful: Propagating Perennials

    Bookmark   March 29, 2008 at 5:20PM
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tapla (mid-MI z5b-6a)

The problem with compost and vermiculite is that they lose their loft and compact "after about .... ohh, .... say 10 minutes." Credit to Rhizo for first using that linesize> In soils, perlite promotes drainage and improves porosity. It's also effective for starting seeds & cuttings. Actually, perlite holds quite a bit of water @ about 3/4 quart per gallon of perlite. The dry weight of perlite is about 7 lbs/cu ft. Wet, it weighs about 18 lbs for the same volume, so it holds more than 2-1/2 times it's weight in water, but since it's soo light, that's not much. It also gives its water up quickly, so has a steep water retention gradient.

Vermiculite is about the same density, and has an even higher capacity for holding water and a very high cation exchange capacity. It also contains some magnesium and potassium that are available for plant uptake, but it is not very durable and will compress if handled when wet. It also has a slightly higher pH than perlite.

Turface is a baked clay granule and the Schultz Corp bags it and labels it as their "Soil Conditioner". This product has more than 13 acres of surface area per lb, which translates to very good water/nutrient retention.

My suggestion for a soil that will hold very good volumes of water and still drain well is:

6 parts Turface or Schultz Soil Conditioner (same thing)
3 parts fine pine bark
1 part sphagnum peat
1 part vermiculite
1 tbsp garden lime (dolomite) per gallon soil
a micronutrient source or use a fertilizer that has all the minor elements.

The compaction factor that makes vermiculite a suspect choice at any notable volume in container soils is a minor issue when the total volume is kept somewhere near 10%, so it's no accident that the volume of vermiculite suggested works out to around 9% in the above mix.


    Bookmark   March 30, 2008 at 12:26PM
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piper101(Z 9b So.Calif)

Thx Al !!!!!

    Bookmark   April 1, 2008 at 10:33PM
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A problem frequently encountered with hanging baskets is how often they need to be watered. For many it can be downright difficult to keep up.

While the potting mix is important may I suggest that it might be a secondary concern (in terms of water retention) to the type of container used?

When I see hanging baskets in stores I generally see plastic containers with a million holes in them or wire baskets intended to be used with fiber linings.

In both cases water loss is going to occur at an elevated rate due to evaporation because of how much air the pot itself allows to touch and dry the mix.

For the life of me I can't understand why 99% of containers intended to be set on a solid surface have impermeable walls (or nearly so) and a single drainage hole on the bottom, but 99% of containers intended to be suspended in the air are incredibly perforated.

Perhaps try lining the hanging basket container with plastic sheeting (like the kind sold in the painting section of the hardware store) and punch a single drainage hole in it. This should slow down the water loss due to evaporation.

    Bookmark   April 1, 2008 at 10:43PM
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Does the Schultz soil conditioner you are recommending say "Clay Soil Conditioner" on the bag?

    Bookmark   April 2, 2008 at 8:48AM
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calistoga_al ca 15 usda 9

On a visit to Victoria, BC fifty years ago I was fascinated by the hanging baskets of flowers on the lampposts throughout the business district. When my inquiries found they required a daily watering I was put off the idea of creating my own. Today I do have some hanging baskets on an automatic drip system that waters every other day during the summer. I use my regular container soil with plants tolerant of some abuse. Al

    Bookmark   April 2, 2008 at 9:47AM
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tapla (mid-MI z5b-6a)

Yes, Gigi.


    Bookmark   April 2, 2008 at 10:51AM
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tapla (mid-MI z5b-6a)

BTW, Piper. JaG made a good catch when he noticed you said "hanging baskets". For some reason, when I read that, I was just thinking of suspended pots and hadn't taken into consideration the fact that there would be so much more evaporative loss from the baskets. My bad! ;o)

His observation that the soil make-up is secondary to the cultural effect of the basket is true. You really should prolly consider lining your baskets with something that will eliminate or at least reduce the surface area exposed to the drying effects of the wind. The soil is still a good choice, but it probably won't go as far toward solving the problem as you'd like w/o incorporating JaG's suggestion or something similar.

Take good care.


    Bookmark   April 2, 2008 at 12:38PM
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PepprGrowr(Zone 5)

Hey guys, just wanted to give my two cents into the mix since I happen to have dealt with all these issues this summer.

We had our deck re-built and extended this year. As a result, we went a little hanging basket mad and now have about 15 - 17 baskets around the deck and hanging from the pergola (new and overly excited gardeners lol).

Of the baskets we have, some were purchased (Basket of fire, tumbling tomato, a couple strawberries, a couple creeping jennys, and 4 cheapo baskets from wal-mart) but the rest were made by hand so that we could A) control what we put in and b) use nicer baskets and c) re-use the baskets year in and out.

When we selected the coir liners, I had no idea that their porous nature meant that they expelled water faster, but having read the other comments, it makes perfect sense! Will have to look into the plastic lining, thanks for the idea!

That said however, we spent some time talking to a gentleman at the local nursery and ended up picking a soil called Faffard Profressional Agro-mix, which is a soilless mixture that includes coir, peat moss, vermiculite, perlite, and a couple others (I couldn't find the list online). It was the same soil that the nursery used for all the plants they grew and we had wanted to make a mix ourselves like Al suggested (though not specifically that mix) but he essentially said that the agro-mix was what we would end up with (for the most part), but without needing to do the mixing ourselves.

The benefit of a soil-less mixture was that it had great water retention, didn't pack down as much as soil did so the roots had plenty of room to grow and because it was an essentially an inert mix (no nutrients in the mix itself), the nutrients could be controlled by us. Furthermore, once the season was over, we *could* just remove the plants and roots, wash out the soil to remove excess salt (a byproduct of coir is that salt build up will happen, though it is dealt with by flushing the plants with water), and then use it next year.

At this point in the summer, I can confidently say that the only baskets doing well are the ones we planted and the basket of fire. Most of the baskets doing poorly look root-bound and while we have provided water daily (when needed) and some miracle-grow for nutrients, they are struggling.

I think I can confidently say that while doing things yourself may be a little more costly and time consuming, the end result is well worth it, especially into the end of the summer.

As a side note, creeping jenny is amazing for baskets! It looks lovely and if you want to hide the basket itself, it hangs over so perfectly.

Cheers guys, hope my input helps. Happy gardening :)

    Bookmark   August 9, 2014 at 8:21PM
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nil13(z21 L.A., CA (Mt. Washington))

If you do the organic thing, I think you will have trouble with awesome hanging baskets in SoCal. You will have to water them so frequently that youwill leach all of the nutrients out of whatever compost you put in there for nutrients.

That said, if you are using the coir liners that typically come with the hanging baskets, you can increase the baskets water retaining abilities by putting in a nice thick layer of long strand sphagnum moss over top of that and then putting in your container medium.

    Bookmark   August 10, 2014 at 12:29PM
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