Deep Dive: From Hot Beds to Hot Dams

New research by Austria's agricultural experiment station Zinsenhof on the age-old method of generating heat from manure: How it works and is it worth it for larger home gardens or market gardeners?

How can early tomatoes and cucumbers be harvested in a four-season climate without the expensive and environmentally unsound practice of large greenhouses heated by fossil fuels? This question has been driving trials at Austria’s agricultural experiment station Zinsenhof since 2010. In March, beds in unheated polytunnels become hot “dams” or mounds to get a head start on the season. Their work seems to have potential for “low-energy” vegetable production in northern market gardens.

Freshly planted tomatoes at the foot of hot dams in an unheated tunnel at Zinsenhof in March. Location is comparable to USDA Zone 7a. ©Wolfgang Palme, 2016

What is a hot bed?

Anyone who has passed by old-fashioned piles of fresh manure has observed steam rising up from them. You can literally see the heat production and at some point long ago people started to capture that heat to extend the growing season. The principle is simple: microbes break down organic material and generate heat in the process. In recent years, hot beds have become popular again thanks to older and younger gardeners alike, most notably influencers Charles Dowding and Huw Richards in England. I highly recommend this excellent article by Brett Gallagher, a market gardener in the Czech Republic, describing how they heat their greenhouse in spring with manure. My focus here is on a commercial application of creating hot dams for growing tomatoes, peppers and cucumbers 6-8 weeks earlier with the dam or hilling technique.