oops...

Kale seedlings on their way out

A couple of days ago we made our first (likely of many) mistakes as beginning growers. We've been really happy with the success of the hotbed system, for its simplicity, its cost (for us, free) and for its effectiveness at keeping seedlings and germinating seeds at optimum temperatures. Unfortunately though, we overlooked a small but important detail when we turned the pile and added new manure on Monday- the pile gives off ammonia for a few days after having been created, which at high levels is toxic to seedlings.

Very sad tomato seedlings, vigorous only two days previous. Apologies for the out-of-focus photo

This is a little ironic, as plants need nitrogen for growth and ammonia is the plant-soluble form of nitrogen produced via the infamous Haber-Bosch process. Provides further evidence for the axiom "everything is poisonous, depending on the dose." 

Fortunately we did not lose much, only a couple flats of tomatoes, kale, and scallions, and we should be able to recover with no problem. It should also be noted that our kohlrabi seedlings, planted at the same time as kale  (and the same species as kale) look great. Yet another reason to love kohlrabi. 

The indestructible kohlrabi 

Anyway, lesson learned. We thought initially that we had killed them by letting them get too cold- the pile takes a few days to heat up, and we thought it had not gotten hot enough to keep seedlings at the right temp overnight. But Daniel correctly identified the ammonia (which you could smell quite readily upon walking into the hoophouse) as the culprit. If we could do it over again, we would have built a new pile, waited for the pile to heat up and for the ammonia to dissipate, and then transferred the seedlings to the new pile, instead of just turning the old pile and putting the seedlings back on it the same day. But the most frustrating part of this whole thing is that the info about ammonia toxicity on hotbeds was out there- just on a document we didn't find until last night...

dammit...

The light at the end of the tunnel is that all of our very young seedlings appear to be fine, it was only the fairly mature ones that were affected. 

Seemingly unaffected germinating onions