How to use compost with seeds and seedlings

My friend Molly moved to Los Angeles. I brought her five buckets of compost in my truck as a welcome gift. “How do I use them to start seeds?” she wondered. It was a good question, and one I tried to answer by rambling forever in an annoying way. I call this “having compost brain.” It’s the condition of understanding that everything to do with making or using compost is relative and interdependent, and that there are often no straightforward answers. How to use your compost with seeds can depend on what type of compost you have, what kind of seeds you have, what the weather’s like, where you live, and what time of year it is. Well, it kind of can. It also doesn’t have to. See what I mean? Compost brain.

To try and de-compost things a bit, though:

There are, of course, “ideal” ways to start your seeds. There’s also just messing around and seeing what happens. Whenever possible, I simply prefer the latter. Don’t sweat the details—just get in there and see what happens. On my second try answering Molly’s question, I simply offered her an experiment.

First, some ground rules

In general, using compost to start seeds works best when the compost is mature and has been sifted, so that it’s a bit lighter and less bulky. If you are starting seeds for growing food, it’s also wise to know where your compost came from: who made it and how did they prepare it? Compost that comes from a “hot” pile represents reduced pathogen risk. (In Molly’s case, she can rest assured that my compost was hot enough, long enough that any pathogens would have been eliminated.) If you’re not sure where your compost came from or how it was prepared, avoid using it to start seeds that will become food. Feel free to use it with non-edible stuff, though.

The experiment

I told Molly to make a few different test pots with the compost I had given her. Some pots would be all compost, others would be a mixture of one part compost to roughly three parts purchased potting soil, and others would be all potting soil. I told her to push one or two seeds into each pot about 1/4 inch down, wet them, put them in a sunny spot, and wait. Within a week, we would check in and see what was growing and look for other things like, are they growing vigorously and tall? Have they grown a lot or a little? Are there any signs of illness? Are some struggling and others thriving?

Voila.

This simple experiment will tell you the ratio of compost that your seeds prefer, and the health and vigor of your plants can be helpful indicators regarding the condition of your compost. Good seedlings generally mean good compost. That’s good to know!

Some people may tell you not to use home compost to start seeds. They will mention that the risks are too high and the tradeoffs insufficient. They will often bring up the the possibility of pathogens, fungal infections, or a nutrient-overload that will harm fragile seedlings.

Sure, sure.

My humble opinion is to generally ignore those people. Seeds and soil (e.g. “compost”) are our most primordial companions. They have figured out how to collaborate with each other across eons of time and I’m not inclined to believe that you putting them together now would be the thing that suddenly disrupts that capacity. So, experiment freely. See what works and what doesn’t, and iterate accordingly. Learn as you go. Look and touch and smell.

Personally, I do like to start my seeds with compost and I do it all the time. I also had a patch of my old garden dedicated to replanting the random stuff that was always spontaneously sprouting from my pile. In general, I do not particularly prefer to pamper my plants, once grown, with highly precise doses of synthetic fertilizers and this-or-that timing and light, etc. It’s just never been my style. I do, however, like to provide them with a solid foundation, which to me means good soil and, yes, that includes compost.

Compost!

Love, Cass

PS. This is Disco, he is “helping” Molly:

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