An experiment

[jillian]

Six weeks ago I started a few dwarf tomato seeds, as well as Santa Fe Grande and Cubanelle peppers. I wanted to test out my seed starting mix. Just for the heck of it I also sowed the same seeds in my own compost with nothing else added. I grow in containers mostly and all my searches on seed starting mix and potting mix left me frustrated. A lot of conflicting info on using compost in container mixes.

So I just transplanted those tomatoes and peppers and there is no difference between the plants. All very healthy. The only difference I noted when transplanting was that the roots were wrapped around the bottom of the seed starting mix, the compost was loose and crumbly but transplanted nicely.

I am surprised, does this make any sense? I am wondering if mixing in a little compost to the potting mix might not be a bad idea. Well I am not an expert by any means. I like to try and figure things out on my own but certainly do not want that to be detrimental to my plants.

Jillian

[Worth1]

Not all compost is the same by far, what one persons results are may not be your own.
They have some composted stuff called dillo dirt here where I live and it has human sewage in it.
I will NOT have this stuff on my place.
Not only does it smell like hog farm for days who knows what is in it.
Worth

[jillian]

lol Worth, this is my own homemade compost. I have read where you most certainly should never add compost to any potting mix, and then I have read potting mix recipes where a third of it is compost. Me thinks me is confused.

[AlittleSalt]

Jillian, I just found this thread. When I experiment with tomatoes and peppers - I grow twice as many as I need. In this case, I would plant half with compost added and the others without it.

[Cole_Robbie]

There are a lot of people who have good results with a 10-15% compost mixture. Whenever I try it, I end up getting stem rot. I think that is because my greenhouse plants in the early spring are exposed to cold nights. I get pythium, aka "damping off." Tobacco farmers call it Falling Over Disease, and it's a problem in cold wet weather. Stems pinch at the soil line and the plant falls over and breaks in half.

Compost is organic matter that feeds bio/fungal life. In good conditions, that food is consumed by beneficial organisms. But in bad conditions, it just cultures pythium.

[Worth1]

Originally Posted by Cole_Robbie

There are a lot of people who have good results with a 10-15% compost mixture. Whenever I try it, I end up getting stem rot. I think that is because my greenhouse plants in the early spring are exposed to cold nights. I get pythium, aka "damping off." Tobacco farmers call it Falling Over Disease, and it's a problem in cold wet weather. Stems pinch at the soil line and the plant falls over and breaks in half.

Compost is organic matter that feeds bio/fungal life. In good conditions, that food is consumed by beneficial organisms. But in bad conditions, it just cultures pythium.

That is the number one reason I wont use it.
Worth

[RayR]

Yes Jillian, there is a lot of conflicting info on using compost in container mixes and here at TV is no exception. Just march on and experiment, your compost is not somebody else's compost. Damping off pathogens, you either have them in your environment or not or you may have them but your biological mix of microorganisms is such that they inhibit the pathogens from infecting your seedlings.

The difference in root growth between your seedlings in your mix and your pure compost could be just a matter of PH. Your compost may have a high PH and used alone may be inhibiting root growth but your compost mixed with other components for your seed starting mix may well be in a sweet spot for PH which is much better for nutrient uptake which will show as more vigorous root growth and top growth. If you have a way of testing the PH of your seed starting medium that can make it much easier to design a successful mix. A good PH meter is best for the task or a colormetric test kit at least.

[jillian]

Originally Posted by RayR

Yes Jillian, there is a lot of conflicting info on using compost in container mixes and here at TV is no exception. Just march on and experiment, your compost is not somebody else's compost. Damping off pathogens, you either have them in your environment or not or you may have them but your biological mix of microorganisms is such that they inhibit the pathogens from infecting your seedlings.

The difference in root growth between your seedlings in your mix and your pure compost could be just a matter of PH. Your compost may have a high PH and used alone may be inhibiting root growth but your compost mixed with other components for your seed starting mix may well be in a sweet spot for PH which is much better for nutrient uptake which will show as more vigorous root growth and top growth. If you have a way of testing the PH of your seed starting medium that can make it much easier to design a successful mix. A good PH meter is best for the task or a colormetric test kit at least.

Thank you RayR for responding, this makes sense to me. I do have a ph meter and tested both my seed starter and compost (alone). Mix was 6.5, compost fluctuated between 6.5 and 7. I am feeling pretty good about my compost, it is mostly made from leaves, vegetable scraps, garden waste, coffee grounds and eggshells. A few chopped up pine needles and grass when we have it. Sometimes I throw some blood meal on it to heat it up quicker.
I am still conflicted whether or not to use in potting mix, just as I am about pine bark. I always test ph of my mixes, my concern is that these will continue to break down and thus create less air space. That is the way I have interpreted what I have read but I am no expert and have lots to learn.
I will probably incorporate about 1/4 compost into my mix, I feel safe with that.
Thanks everyone for the replies!:

[RayR]

Originally Posted by jillian

Thank you RayR for responding, this makes sense to me. I do have a ph meter and tested both my seed starter and compost (alone). Mix was 6.5, compost fluctuated between 6.5 and 7. I am feeling pretty good about my compost, it is mostly made from leaves, vegetable scraps, garden waste, coffee grounds and eggshells. A few chopped up pine needles and grass when we have it. Sometimes I throw some blood meal on it to heat it up quicker.
I am still conflicted whether or not to use in potting mix, just as I am about pine bark. I always test ph of my mixes, my concern is that these will continue to break down and thus create less air space. That is the way I have interpreted what I have read but I am no expert and have lots to learn.
I will probably incorporate about 1/4 compost into my mix, I feel safe with that.
Thanks everyone for the replies!:

I wouldn't think that PH is an issue since you are in the neutral to slightly acidic PH range which is excellent. Do you check the PH over a period of time? There is a tendency sometimes for an upward PH drift over a couple of days to a week after the medium is wet.
The other big factors are the air space between the aggregates and water retention. Not enough oxygen penetration and too much water retention would inhibit root growth. That could be a problem with straight compost alone that is well finished where the particle sizes are very fine.
You are on the right track thinking this through and experimenting to find the right balance. I've come to appreciate the amount of effort that is takes to engineer good commercial seed starting mixes and potting soils. It's not just slapping together inputs and hoping for the best.

What are your components in your seed starting mix?

[jillian]

Originally Posted by RayR

I wouldn't think that PH is an issue since you are in the neutral to slightly acidic PH range which is excellent. Do you check the PH over a period of time? There is a tendency sometimes for an upward PH drift over a couple of days to a week after the medium is wet.
The other big factors are the air space between the aggregates and water retention. Not enough oxygen penetration and too much water retention would inhibit root growth. That could be a problem with straight compost alone that is well finished where the particle sizes are very fine.
You are on the right track thinking this through and experimenting to find the right balance. I've come to appreciate the amount of effort that is takes to engineer good commercial seed starting mixes and potting soils. It's not just slapping together inputs and hoping for the best.

What are your components in your seed starting mix?

Thanks RayR, I really appreciate your input. My seed starting recipe:

peat moss
perlite
vermiculite
sta green garden soil (I know I know, just a little)
garden tone (espoma) small amount
worm castings

I have great results with this mix. I love the espoma for the beneficial microbes hence why I add a little garden soil. I really need to start posting some pics.....I never take time to do it. I recently transplanted kale, thyme, parsley and the "experimental" dwarf tomatoes and peppers into solo cups and they are looking great. I have several varieties of peppers and lettuce under grow lights. Started 40 varieties of tomato seeds Thursday so I am super excited!

[jillian]

Oh and I might add that the reason I transplanted into solo cups is that they have grown so much and is too early to plant out! I used the larger cells thinking I could just leave them in there until planting out time, but not the case.

[RayR]

Originally Posted by jillian

Thanks RayR, I really appreciate your input. My seed starting recipe:

peat moss
perlite
vermiculite
sta green garden soil (I know I know, just a little)
garden tone (espoma) small amount
worm castings

I have great results with this mix. I love the espoma for the beneficial microbes hence why I add a little garden soil. I really need to start posting some pics.....I never take time to do it. I recently transplanted kale, thyme, parsley and the "experimental" dwarf tomatoes and peppers into solo cups and they are looking great. I have several varieties of peppers and lettuce under grow lights. Started 40 varieties of tomato seeds Thursday so I am super excited!

If the mix is successful then that's great.
There is a 1001 ways to put together a mix and many of them wrong. I once threw a mix together, a little of this and a little of that kind of thing, whatever sounded good, just to see what would happen. It ended up being all wrong, the PH ended up drifting to 8.25. Lettuce seedlings planted in it suffered greatly. I ended up cutting the mix 50:50 with some peat at PH 5.5 and brought the PH down to a stable 6.7. The plants then grew great in that.
You can have everything right in a mix like good drainage and aeration but if the PH is way off the idea range it's going to fail.