What is the best growing medium for Sub Irrigation Planters (SIP-ing)?

Question

Hello, All!

Here's the deal: I'm really getting fascinated by Sub Irrigation Planters! The concept is just too, well, NEAT not to spend some time with!!!!

My question is about beginning seeds in them, and the best soil. I've currently got some herb seeds in some SIP's made out of 20-oz water bottles, using "Miracle Grow Planting Soil."

Then I have 2 2-liter soda bottle SIPS with lettuce seeds in them, one with an organic potting soil compound (lots of chunks of wood in this one) and one with "Mel's Mix" (1/3 vermiculite, 1/3 peat moss, 1/3 blended compost). I figured the absorbancy of the vermiculite would be good for wicking.

Finally, inspired by Greenscaper (from a blog I visit), I have an all-recycled SIP made out of an old waste basket, a plastic apple-juice jar as the water chamber, water bottles making a fill tube, and an old straw as a drain tube. In that I have some arugala and red lettuce seeds.

My question is this. I watered all of my planters from the top for the first time, and then made sure that I have water in the chambers. The 2 potting soils are holding their water well, and feel really damp. The Mel's mix, on the other hand, feels really dry on top. I stuck my finger in about an inch or so, and it felt really dry all the way down. I actually gave in an put a little bit of water on the top, as I want the seeds to have the moisture they need to sprout (these planters are all less than a week old. So, various questions:

1) Is the "Mel's Mix a good choice for this type of gardening, or would some other choices be better?

2) What is the best growth medium for an SIP-type container?

3) Am I better off planting seeds in the SIP's, or sprouting the seeds elsewhere, and then transplanting them into the SIP when it has the root system established?

4) Are these intelligent questions, or am I just going through the normal, "I planted seeds and will be anxious until I see some kind of plant coming up" anxiety? (anyone else get that?????).

5) Do I even want to worry about the soil looking and feeling dry on top? Is there enough water absorbed in the vermiculite to give the seeds what they need, even though it looks dry to my eye and feel?

I plan on doing a lot more of these type of containers, and am in uncharted territory (I'm actually a neophyte to growing my own food as a whole), so I'd love any tips, resources you'd like to share.

Thanks!
Tom

Answer 1

"I figured the absorbency of the vermiculite would be good for wicking."--you figured wrong. vermiculite dries out fast, very fast. you need a medium that will hold the moisture. you can correct this by adding more compost to the medium (this is so you won't waste what you already have purchased) BTW: when I started out, I figured the same thing until I had my Homer Simpson moment.



1. Mel's Mix is not a good choice for this type of gardening. cut back on the vermiculite or eliminate it all together. heck for that matter, straight compost would be great.



2. almost any type of potting medium you would use in your garden or flower pots, so long as the medium holds moisture well.



3. since you're doing small containers, you're better off planting the seed directly into the SIP.



4. these are intelligent newbie questions & you are going through the nomal newbie anxiety of "is it a plant yet?"



5. yes, the faster your soil dries out the faster your SIP will use up water. most SIPs instructions recommend that you mulch the surface which will also help hold in moisture. you can use decorative stones if they are small enough containers.



if your planting medium looks & feels dry, you need more water.







I've been doing SIPs for a couple of years now. I'm advancing to a yard sized one. do a search on "wicking beds". you'll get the Australian sites. really fascinating & awesome stuff.



I've put in a few links to some of my favorite sites

Answer 2

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Answer 3

Sub-irrigated Planters

Answer 4

Hi Tom,



You raise some good questions. Although it's rather late, allow me to answer your question for the benefit of others who are wondering the same thing as you.



To start off, I'm going to answer you in the context of a container based SIP. This info is not intended to address an in-ground sub-irrigated bed. Actually, depending on what you want to grow, and what climate you live in, an in-ground sub-irrigated bed might not be a good idea at all.



OK, so for container based SIPs:



Do not use Mel's mix. Instead, Earthbox recommends "a peat-based (70%-80%) growing media that contains perlite or vermiculite." They've tested and refined their system for years. So you could, for example, use 7 parts peat moss + 2 parts perlite + 1 part vermiculite. That will get you started.



What else could you use? I've included coir (coco) and pine park fines. But using compost, is actually NOT advised for a container set up. You can try it. It may work. But it is not ideal.



A good SIP needs strong wicking (capillary action) along with pore spaces that provide aeration. I have lots of good info that may help you here: http://albopepper.com/sips.php



As for the top drying out, this is very bad if you are starting seeds in the actual SIP. Mist daily or as needed from the top. Do not allow the top to get dry while seeds or germinating or even for a week or two thereafter. Once the seedlings have one or two sets of true leaves, they will have an established root system that will reach down into the moisture of your SIP. Now you can stop top watering.



Keep an eye on moisture in small, shallow SIPs. I've seen seedlings that were stunted by TOO much moisture. I had to let the soil dry slightly, then the seedlings took off. As they got bigger, excess moisture was never a problem. It's not that hard if you know what to look for.



But, if you'd prefer to grow seedlings in trays and then transplant later, that would work too.

Answer 5

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