Hello everybody,

I need an advice on soil preparation for pots. Last year I bought $200 worth of potting soil mix in bags and after harvesting about 6-8 lb of tomatoes it does not seem as a shrewd investment. At the same time last year I got a lot of free spent mushroom soil which seems to be in a great condition. It is as black is it could be (the blackest soil I ever saw). I added it last year to several pots and it seems work well. This year I found a local horse stable business which offered free compost (as much as you want). It is three year old fermented horse manure mixed with wood dust and straw. It is completely composted and the owner said that he grows his strawberries in the compost without any additions with great success. He said that I can grow tomatoes directly in the compost provided that I add good amount of lime of egg shells to prevent bottom end rot. And finally we have a stump om out property which the whole last year we stuffed with all vegetable and grain waste. The stump had a big hole in the center and we just through kitchen waste in it after we realized that trying to compost in a bucket is not really pleasant experience. To my surprise I harvested about 15 gallons of stump compost this string, however, it seems that good part of it is a wood composted from the stump body. What I am really missing is mineral soil since the original soil in my back yard is primarily stones and very little of real soil. It is hard to dig a 5 gallon bucket of soil here.

And finally, last year I got septoria leaf spot on all my tomatoes and I an concern about the previous years mushroom soil may still have it.

First: is it true that I can add lime to compost and grow tomatoes in this mix without anything else? Then, should I use my old mushroom soil which looks really great? And finally: do I have to mix additions like peat moss and mineral soil (I can but top soil I guess)?
Thank you in advance and sorry for long writing.

A lot of this depends on a couple factors. The amount of produce that will come from the garden and pots is important.

Tomatoes are heavy feeders, and if you plan on a large harvest, then you'll need to add more compost or fertilizer mid season.

As for micro-minerals, depending on the compost, that should be sufficient.

Attempting to container grow tomatoes will always be disappointing.
If you want happy tomatoes, spread all the mushroom compost/horse manure/stump compost across the rocks in your back yard. after gardening on top of the rocks, you should soon see decent results.
When I garden on top of rocks, i attempt to find soil using a mattock... but, simply spreading the current mix a foot or more thick should yield decent results... I'd use fallen logs as borders for the tomato bed.
While it is possible to just use your current mix in a container, the tomatoes will remain stunted due to the lack of root room.
When I pull tomato plants out of the ground, they have roots that can reach 20 feet... add in the value of the mycelium and they can be gaining nutrients from 3 times that distance... makes a lot of difference!

stone wrote: ↑Sun May 16, 2021 3:23 pm When I pull tomato plants out of the ground, they have roots that can reach 20 feet... add in the value of the mycelium and they can be gaining nutrients from 3 times that distance... makes a lot of difference!

Do you really mean 20 ft and not 20"
That explains why tomatoes grow better in ground, not in containers!!!
My problems that all the bears, deers, squirrels etc will take them all. I have to grow in containers on a deck to compete against racoons, squirrels and chipmunks only

2 cu ft potting soil bag slit and holes punched into the bottom for drainage,plant right in the bag.

A lot of us container growers do re-use our soil. As long as you removed the plant material at the end of season and compost it elsewhere, there should not be any septoria or other fungal disease. These only overwinter on plant material, not in the soil. Unfortunately they are in the environment so you will probably see them again anyway, but the used mushroom compost should be fine.
Rockoe is right that if you want a high yield, you will need more fertilizer ... but Stone is right too, that the container volume limits what they can do. Unless you use plenty of fertilizer at planting, and supplement wiith liquid ferts, you will get smaller yields.
I'm using some composted horse manure in my containers this year, not alone but mixed at 1/3 with last year's recycle. First time I've done horse manure in containers, so maybe we can compare results. I can see a very small wood chip still in there, which concerns me a bit, as your friend said, lime is important but also may need extra N ferts to compensate for unrotted wood. I also added some garden compost, kelp meal, and will use bone meal in the hole when I plant. If I see yellow leaves, I will add some fish emulsion fert to compensate for the wood chip.
I don't personally use much peat and I would avoid mineral soil for anything more than a dusting in the mix. Mineral soil is pretty poor for container growing. Compost retains moisture very well, so you don't need peat - it has no nutrients either so not your best bet for a yield.
I believe the 'soil-less container mix' idea, using peat, bark fines etc all of which contain no nutrients, is based on the idea of constantly feeding liquid ferts. This is a different approach completely, compared to simply compost of various kinds.

@Bower, I appreciate you confirmation that using mostly compost is a safe option. How much lime should I add? Is it true that I can get a decent yield if I use sufficient amount of fertilizer? I am planning to re-post tomorrow - do I need to add in in the soil of I will start two weeks later after the plants will take first "easy fruit" nutrients from the compost? I got left over from last year of Sta-Green Plant Food 24-8-16. Is it any good? Why would chips are bad? In the potting bags which I bought for $$$ at Lowe's there are a lot of half composted wood chips. I used that potting mix to start seedlings and I think the result is pretty mixed, but when plants getting bigger they grow OK.

slugworth wrote: ↑Sun May 16, 2021 6:46 pm 2 cu ft potting soil bag slit and holes punched into the bottom for drainage,plant right in the bag.

I was shopping for grow bags when your message came Are grow bags still better - they are reasonable inexpensive. I am thinking about 10 gallons bags. BTW - how many gallons are in 2 cu ft?

[mention]Barmaley[/mention] I don't measure lime but just use a small handful and sprinkle over the top then dig it in.

The problem with wood chips, they will tie up nitrogen in the soil during the breakdown process. On the positive side they may help with moisture retention. Woody material is fine in the soil-less system because it soaks up the liquid ferts, thus doesn't cause the same issues as with a mainly compost system in which you expect the plant to take nutrients from the soil.

If the 24-8-16 is granular, I would use just a small amount per container maybe no more than a tablespoon per 5 gallons and mix it right through the soil before planting. If it's a liquid fert then keep it for diluted feeding when the plants start to ripen their fruit or if they show signs of deficiency then before that. Too much N will tend to produce foliage instead of flowers and fruit, but the high N and K should be fine for tomatoes to ripen up. I do like to use bone meal (10-14-0) at planting, because the high P helps to get a good fruit set, and using kelp for K. But as they say every year is an experiment, and if you work with natural materials then even more so. You may get a better answer from others, who have more experience with the NPK labeled products. The pelleted chicken manure that I've used was either 5-4-3 or 5-3-2. So you can see, your fertilizer product is a lot more concentrated. The usual value for plain compost is 1-1-1.

Brownrexx grows tomatoes in compost without additional fertilizer. I have done it too, years ago, but I never had high yields. Just great tasting tomatoes. But if you want to increase yield, fertilizer is the answer, for sure. Especially in containers.

I do not garden in containers but I have used lots of mushroom soil as an amendment in my gardens. Here is a link from Penn State that may be interesting. They have analyzed mushroom substrate in their labs and they consider it to be a great amendment but not such a great fertilizer since the nutrient content is low.

https://extension.psu.edu/spent-mushroom-substrate


Edit: I just read [mention]Bower[/mention] post and it is slightly misleading. I don't grow my tomatoes in pure compost. I grow them in my garden soil that is amended with compost. I do not add additional fertilizers except some feather meal in the hole at planting time and I get more tomatoes that I can ever use.

I have had soil tests and my soil has plenty of nutrients but since Nitrogen is so volatile, it is recommended to add it every year. Feather meal is organic and it is 12-0-0.

Start with a good potting mix and that will last you for years. The nutrients in it don't matter. The components of potting mixes generally have no nutrients, it's all added afterwards by the producer and you can do the same.

You can just amend with normal organic pelleted fertilizer of your choice or (easier) mineral fertilizers in liquid or powder form (the organic way is more difficult in pots, but can be done with pretty good results).

A good potting mix is one with good aerated structure that will last. Coarse peat based is imo the best, but I find it's not really that easy to find since most retail potting mixes nowadays seems to be more of a forest compost. What nurseries use for their sold bushes in pots, that's the stuff you usually want, so ask one.

You can grow in pure compost. I think the composted horse manure sounds better than the mushroom compost. The mushroom compost is a very fine material that is not great for aeration, horse manure has a much more gritty structure, the only problem is if it will burn the plants (no idea, I have heard people saying they plant directly as well). Maybe a mixture of both, with more horse than mushroom would be a good idea. I think the mushroom compost would be a good source of humic acids considering the black color.

Bower wrote: ↑Mon May 17, 2021 7:22 am

Brownrexx grows tomatoes in compost without additional fertilizer. I have done it too, years ago, but I never had high yields. Just great tasting tomatoes. But if you want to increase yield, fertilizer is the answer, for sure. Especially in containers.

If I can choose high yield of great taste I will go for great taste. What can I do to increase the taste even at the cost of low production? Can I keep them both high? I don't mind to accept substantial decrease in production if the taste improves slightly.

One way to improve taste at the cost of some production is to increase the salt content of the growing medium. By salts I mean usually nutrient salts, I think it's a bad idea to use table salt, as sodium has some extra side effects. This usually happens naturally if you use mineral fertilizers and don't flush the container often, the plant takes what it wants and then some parts are not needed, and it accumulates slowly.

mama_lor wrote: ↑Mon May 17, 2021 9:31 am One way to improve taste at the cost of some production is to increase the salt content of the growing medium. By salts I mean usually nutrient salts, I think it's a bad idea to use table salt, as sodium has some extra side effects. This usually happens naturally if you use mineral fertilizers and don't flush the container often, the plant takes what it wants and then some parts are not needed, and it accumulates slowly.

Are we talking about Epsom salt?

Barmaley wrote: ↑Sun May 16, 2021 9:02 pm I was shopping for grow bags when your message came Are grow bags still better - they are reasonable inexpensive. I am thinking about 10 gallons bags. BTW - how many gallons are in 2 cu ft?

A lot of places don't sell grow bags.
I don't know about the gallon conversion,but for a quicky planting solution it is ideal.
I don't use this method often,it was just for research.
I had the topsy turvy tomato planters but they don't last.
After 1 season they fell apart.

Well.... I would dial back on the salt idea. Especially for a beginner looking for a good basic formula to grow with compost in containers. This is something you might try as an experiment with a few plants, when you already know what you are expecting from your basic method.

The one generality for improving taste is not to over-water. This can be an issue with containers in hot weather. You more or less have to water a lot in some circumstances. So plan your grow to keep the roots an even temperature if you can, and mulch to reduce the need for watering.

They also say that sweetness enhances other flavors. Potassium is the important nutrient for that.

For the rest of it, the variety of tomatoes determines your basic taste profile.
Everything you do or don't do (including the weather, fertilizer, watering, etc) can only build on the taste genetics that is there to begin with.

And different varieties will be more or less sensitive to the kind of treatments that might in some cases produce less but tastier fruit.
Some varieties do really well in "dry farmed" conditions and produce tasty fruit that way.
But other varieties might be overstressed and not produce well or at all in those conditions.
One I grew called Altajskiy Urozajnij produced only a few, small, but really delicious fruits when grown in a 5 gallon pot outdoors in a really nasty cold year. They year afterwards I gave it a prime spot in the greenhouse heat, with a bigger container. It produced a ton of fruit and they were also larger. They were sweet but quite lacking the intense flavor of the previous year.
OTOH there are a lot of deservedly famous tomatoes that won't tolerate cold nor a small container either, whatsoever. Lots of tomatoes if not the majority will not develop good flavor in the cold, and why the first of the season are often not so good.
What I'm saying is, so much depends on the variety.
Cherries and small tomatoes do fine in low container volume and lower nutrient systems.
Big beefs need big containers and lots of nutrients to do their thing.
Experiment and find what works for you.

Barmaley wrote: ↑Sun May 16, 2021 6:01 pm

stone wrote: ↑Sun May 16, 2021 3:23 pm When I pull tomato plants out of the ground, they have roots that can reach 20 feet... add in the value of the mycelium and they can be gaining nutrients from 3 times that distance... makes a lot of difference!

Do you really mean 20 ft and not 20"

That explains why tomatoes grow better in ground, not in containers!!!
My problems that all the bears, deers, squirrels etc will take them all. I have to grow in containers on a deck to compete against racoons, squirrels and chipmunks only

Maybe more than 20 feet...

Dunno 'bout the bears... Davy Crocket had a solution... In the song, he shot one when he was only 3!
The deer are easily deterred by a fence placed inside the tree line obscured by lots of brush, vines and such...

Raccoons, chipmunks, squirrels?
May require permanent solutions... they used to eat them... squirrel tastes like duck... the cats love the taste of chipmunk...
raccoon? Maybe trap and offer to the local people that eat them... I've met a lot of people around here that would take all I can trap...

Edit:
You know...
If I was trying to grow tomatoes in the Mtns of PA, I'd build a cage over the area I had using a combination of methods... between how I protect the chickens from raccoons, and how I protect the peas from rabbits.

All those critters will come up to the deck and pick munchies.