Compost in Seedling Mix

I’m a believer in compost but I’m not such an avid believer that you should grow in 100% compost as many claim you should.

This is mainly because compost can be pretty fine in particle size and this can lead to compaction and lack of airflow around the roots.

Young seedlings need plenty of air around their small, delicate roots to grow optimally. Compost doesn’t help with this if you’re growing in only that entirely.

This is why I think you need to start with a seedling mix that promotes airflow and water retention at the same time. I personally like to use Gary’s Top Pot because it has more airflow components than water retention components. It’s about 66% airflow to 33% water retention.

Perlite, pumice and sand are going to keep that soil mix from compacting. The peat moss is what holds the water.

Like I said, I’m a big fan of compost. It does many great things. One of the things I like is that it can turn something like Gary’s Top Pot into a living soil because of the millions of organisms in the compost.

Another reason is that it provides slow-release nutrition that will help the young plants grow at a balanced pace.

So what’s the ideal amount of compost to put in a seedling mix? Right now I am trialing a few different ratios.

Here’s what we got going on right now:

15:1 Top Pot to Malibu Compost

14:2 Top Pot to Malibu Compost

12:4 Top Pot to Malibu Compost

I’m not doing any more than 25%. I should add a 13:3 ratio just for good measure but what I want to see is what is the minimum amount we need to see it work for our seedlings.

I know that 25% is the max we want to amend because there’s going to be too much nutrition the higher we go.

I also try to bottom water seedlings so that they don’t fall over or their stems get damaged from irrigating. I’ve had problems with compost sitting in the water so I’m trying to see what I can get away with here.

I’ll post an update on this trial to show which had the best growth.