Soil Mix for tomatoes and veggies

Scott Henry · Jul 29, 2020

Hello All ,

I'm new here and appreciate all of your great dialog and knowledge, particularly in the where to find supplies for 5:1:1 and gritty mix potting mixes in Vancouver thread.

@Tom Hulse
I have been using a high quality commercial potting spoil for my tomatoes and veggies and it has worked ok but I am looking to step it up and make my own soil mix. I have been considering the 5-1-1 mix mentioned above. However, the bark fines are extremely difficult to source here in Southern California so I am leaning toward something else. I am intrigued by your mix and wonder if you wouldn't mind sharing it. My primary goals are a better soil and ideally something that is cheaper than the bagged stuff.

For reference, I am in the Los Angeles area about 2 miles from the coast so it doesn't get too hot here, rarely above 80. My containers are 25-30 gl smart pots and I also plant in raised beds. We plant a wide variety of veggies but I am starting to focus on tomatoes and I am currently growing about 7 heirloom varieties, from cherries to San Marzano Redorta's.

Any guidance is much appreciated!

Thanks,
Scott

Tom Hulse said: ↑

Hi Tom, sorry for the slow reply! I'm not familiar with "water lenses" in soil. I know Al frequently talks about perched water at the bottom of pots, is that what you mean?

The first problem I have with bark is it's poor ability to transfer water up and throughout the pot to even out the moisture content. Evenly distributed moisture is the real golden sword that helps you prevent overwatering. It makes the surface of the soil, where you can see and touch it, very similar in moisture content to the very bottom middle of the pot. This lets you know easily when you should water and avoids waterlogged foul stinking rotting pot bottoms that so often kill houseplants and container plants in general. So to prevent that in a bark mix, Al's mix uses a coarser overall mix than most any commercially available mix, so it's much more difficult for the mix to hold water. This works great, and so I think many people can have great success with Al's mix, but in order to do that, you have to be able to water your plants more frequently, much more frequently than all traditional mixes (that's a huge inconvenience for me and also limits the plant's potential). If you happen to find a finer, more water-holding grade of bark that lets you water like normal mixes, then you get back to the problem of that perched water at the pot bottom not ever drying enough, and it also breaks down much faster.

Which brings me to my second problem with bark: it's instability over time. It just breaks down and changes it's moisture retention far too much for me. I've seen several experienced growers who said the 5:1:1 mix was great/fine for the first year, but were disappointed with how it changed the second season. We all see it happen when you put bark on your garden beds, it just gets eaten up quickly.

Now that does happen also with peat, but not nearly as much. Al makes all kinds of wild claims about how peat breaks down, collapses, compacts, packs, etc., but it just doesn't, especially when mixed with other ingredients. That's why peat is the #1 potting soil ingredient in the world used by professional growers. Peat has been sitting there waterlogged in a bog for thousands of years. Most of it's composting is already done, so it lasts an amazing amount of time compared to how much water it will hold, and it's unique structure helps it hold air as well as water. That's why it is tops among the real experts worldwide.

Peat also does definitely get perched water, you can see it after you fully water a pot, then tilt it at an angle to reduce the perched water a pot will hold. However, unlike bark, it moves this water up and throughout the pot. It will evaporate water from the surface more than twice as fast as bark mixes because that water is moving up. So no death zone in the bottom middle of the pot that stays wet even when you think the surface is fully dried out.

If you use a mix similar to mine, please keep in mind that I commonly add more drainage material for many types of plants, like palms for instance.

I got my last small batch of pumice from Indoor Sun Shoppe in Seattle in 1 or 2 cu. ft. bags. There's also a landscape supply place in (Puyallup?) that sells it by the truckload for bigger batches. If you need that reference I'll dig it up.
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Soil Mix for tomatoes and veggies

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