Let’s Play With Dirt – How to make moisture control soil.

Quality dirt means productive plants. Healthy soil is not measured merely on the level of nutrients. Other factors must be considered as well. A soil can be high in organics and composted material, but it the roots can’t breathe, the plant won’t thrive. High clay content, pasty soil, and poor nutrition can all make plants weak and unfruitful.

I made the mistake of building several beds with organic soil alone, and the results were not good. The plants got off to a fast start, but as they grew, they became root bound. When watered, the soil became pasty and this is very hard on plants. It’s only slightly better than growing plants in clay.

For soil to be healthy for plants, it must have good organic matter, very good drainage, and have the ability to hold moisture. If any of these are missing, the plant won’t thrive as it could. For a good example, check out my article on Root Health by clicking here. In that article, I show a tomato grown in rich organic soil that struggled. I dug it up and reworked the soil and it began thriving. The soil was rich, full of organic matter, held moisture well, but had poor drainage. Since the roots couldn’t breathe, the plant couldn’t thrive. Once this problem was fixed, it became very productive.

In the past, I built a lot of my beds with moisture control potting mixes from local retailers. This works very well, but has two main drawbacks.

1. It is very expensive. Each year the price goes up, or the size of the bag goes down. As of this writing, a large bag of moisture control mix is around $14 for 1.5 or 2 cubic feet, depending on the brand. Since it takes about three bags to top off a 4 foot by 4 foot bed, the expense can be high.

2. It contains chemical fertilizers. Almost every commercial mix is ‘enriched’ with chemical fertilizers. Plus most of these are time released, so it can be the entire growing season before you can add organic fertilizers. Even then, it takes months to flush the chemicals from the soil. So you are going to have a build up of salts and fertilizer from the beginning.

However, the moisture control blends do work well. If you don’t care what type of chemicals you are adding to the soil, then these commercial mixes will work for you. However, if you want to use organic fertilizer, keep healthy microbes thriving in the soil, and have a long term healthy garden, these mixes are not the solution. There is a reason why it is suggested that the soil be replaced every year. Once the fertilizer serves its purpose, the soil is dead. See my article on compost tea to understand what makes soil thrive.

For 1/3 and sometimes 1/4 of the cost, you can build your own blend of moisture control soil and have it without chemical fertilizers. A healthy blend contains Peat Moss, dirt1Mushroom compost, Potting or top soil, and perlite. All of these are inexpensive and available at your local gardening center. Perlite might be a little harder to find in bulk, but if you have a grow store, it’s fairly cheap – $20-25 for 4 cubit feet. This is enough to last for a long time. Buy the fine perlite and not the course one.

Also note, the ‘home size’ peat is often fortified or enriched. That means it has been soaked in fertilizer. The bulk size is unfertilized and is cheaper. About $9 for 3 cubit feet.

In this article, I am going to build a 4×4 bed. You want to have at least six inches of soil. This is around 6 cubic feet of material. In this method, don’t waste the money on expensive potting soil. Just plain – dollar a bag – potting soil is fine. We will enrich the soil with mushroom compost. The peat moss and perlite serve as moisture control and drainage. I have the equivalent of 3 gallons of perlite in my six gallon bucket. That is sufficient for a 4×4 bed.

I’m also on a patch of ground that is slightly uneven. To keep the soil from running out, if pinstrawit’s a small gap, pack a little pine straw in the gaps.

If the ground is very uneven, plug the gaps with bricks or rocks, then pack in a little pine straw. Once the dirt settles, it won’t run out.

Also, make sure you have good weed block below the bed. Weeds will invade your garden – especially once they detect the rich soil and moisture. If you have Bermuda grass, good luck. It laughs at weed block. It may take a while, but Bermuda grass (sometimes called centipede grass) will bore through weed block. I’ve laid three layers of commercial grade weed fabric, and it still bored through. The only solution I’ve found is to lay down plastic, and then put weed fabric on top of the plastic. The plastic will stop Bermuda grass and the fabric will insulate your roots from the plastic. Moisture doesn’t soak through plastic, so it can rot roots touching the plastic.

Pour half a bag of mushroom compost, one bag of soil, and about one cubic foot of peat dirt2(a third of a bag). Pour a generous amount of perlite into the mix.

A word of caution – wear a dust mask. Perlite dust isn’t healthy, and dry peat will put up a cloud of brown dust. It’s never good to breathe heavy dust of any kind. You’ll be glad you wore a mask!

Now it’s time to get your fingernails dirty. work the ingredients together. Once you are confident all the materials are well mixed, repeat the process. Keep mixing until the bed is topped off.

Water the bed well.

Dry peat doesn’t quickly absorb water, so give it a good shower several times, allowing it to soak well between waterings. Once the soil is thoroughly moist, it will retain water well, and the drainage will be very good. You will probably have enough peat left over for about 5 gallons of soil mix. Enough for a nice earth box / self watering container.

Updated 04/24/13: I’ve recently started using Coconut Coir and have found it to be better at keeping the soil evenly moist than peat. It normally comes in compressed bricks or 5 kilo blocks. Expand by soaking in water and add just as you would peat.

Also note that you’ll need to add nutrients throughout the growing season. You can do this by adding more compost or supplementing with either organic or non-organic fertilizers. Store bought potting soil is fortified with chemical based fertilizers. Instead of chemical fertilizers (which weaken the soil over time), I like to add kelp meal, blood meal, bone meal, azomite, and other natural nutrients. Water bi-weekly with organic tea one week and fish emulsion the next. For tomatoes, I add tomato tone once a month. It’s organic and very beneficial to plants.

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Eddie Snipes 2012
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Let’s Play With Dirt – How to make moisture control soil. — 4 Comments

  1. Excellent article on creating organic soil with moisture control. It is always fun playing in the dirt (or with dirt) The tip on wearing nose and mouth protection is a very good tip, I often get a dust cloud when I am using peat moss, though I like to moisten my soil additive like Perlite before I add to my soil mixes. Happy Gardening!

  2. Hey Joe. Thanks for stopping by. Adding a little moister is a good option to avoid dust. I’m a dry mixer myself. For me, it seems to be easier to mix it all together. Thanks for adding your tip. It’s another option for readers to try :)

  3. I enjoyed this article. I am looking to make this mix for my aging mother’s standing table garden. Question: is one, 5kilo block of coconut coir sufficient to substitute for the peat moss based on the entire ‘recipe’ ratio?

    • In my opinion, CocoCoir is much better than peat moss. It is a perfect substitute. I like it better because it absorbs water much better than peat. Plus, if peat gets dried out, it takes a lot to get it rehydrated. Peat tends to repel water until it gets moist again. Coir does not do this. I no longer use peat moss at all – even in my outdoor raised beds.

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