Ginger Group Session 6 – Hotbed and Bark

After months of preparation the Ginger Group is finally ready to build and plant our hotbed of gingers.

The raw hotbed

A hotbed is an old horticultural technique using fresh manure to provide a heat source that will artificially heat a bed sufficiently to enable growth earlier in the year than would otherwise be possible. Victorians used this technique for pineapples and melons. Now the method is favoured especially by the no-dig and permaculture communities to give an early start to tomatoes and chillies in situations where no other energy source is available.

That’s certainly the case in the lower greenhouse where electricity is only a distant memory of the eighties when it was part of a Lambeth horticultural initiative to grow bedding and perennials for the borough’s parks. We’ve built a central bed of 6.4m x 1.6m and 90cm high. The bottom 40cm has already been filled with fresh manure by the intrepid crew from Michael Tippett School – thanks, guys; and with manure donated by Ebony Horse Club. The manure has been compressed and covered with Mypex. You can build your own hotbed with four pallets – read all about it in the Charles Dowding blog. The temperature of the compressed manure is around 45°C.

On top of the manure we will put 4000l of Melcourt Nursery Stock compost, 1000l of Melcourt Potting bark. Initial nutrition is provided by 3kg of seaweed meal, 10kg of rock dust and 20kg of Biochar. We’ve already put the first 3000l of stock compost in place. This completely peat-free compost mix emulates the natural growing environment of the gingers we will be planting which in the main are plants of the forest floor of South and South East Asia.

The nursery stock compost contain bark particles from 1-6mm and the potting bark from 3-15mm. Both these composts are exceptionally free-draining and the range of particle sizes ensure that there is plenty of air around the roots – the combination provides an air-filled porosity of around 33% by volume. The composts are easy to wet and yet don’t hold massive amounts of water. Our experiments over the last two years show the composts have excellent durability and provide a consistent structure throughout the season.

Seaweed meal is a slow release fertiliser and soil conditioner, rich in trace elements and amino acids and which stimulates microbial activity, improving soil structure and fertility. Volcanic rock dust adds essential minerals and trace elements including Iron (Fe), Copper (Cu), Zinc (Z), Manganese (Mn), Molybdenum (Mo), Cobalt (Co), Chromium (Cr), Selenium (Se), Boron (B) and Iodine (I).

GroChar is a modern take on a 2000 year old tradition, GroChar was inspired by Amazonian Indians who used charred plant matter to enrich their poor, infertile soils. The fertiliser provides a balanced 5-5-5 nutrition.

The char remains in the compost almost indefinitely, improving soil structure and water penetration, helping retention of nitrogen and continuing to absorb additional carbon from the air. This is an experiment for us but it comes highly recommended. You can take a look at the GroChar videos featuring Alys Fowler and read a guide to using GroChar. We are using this organic product in lieu other granular fertiliser and also instead of horticultural charcoal – both of which would otherwise been in our mix.

Once the compost is on top of the manure the compost will warm. Our target if to get the compost to above 30°C by the end of the month. We’ll be planting the specimens that were identified last November and have been kept in the lower greenhouse under fleece during the winter. We also have some plants in the hot propagator but we won’t move these until the bed has heated up. After planting almost all the bed will be fleeced as we haven’t had the last of the cold weather yet. Fortunately, an overnight frost won’t lower the compost temperature very much and the fleece will protect young growth above the ground.

On the plan below we aim to plant H. coronarium, A. zerumbet, Fingeroot, H. spicatum, Turmeric, Z. mioga, H. flavescens, Cautleya and H. stenopetalum on Sunday.


Ginger House Central Bed Plan

Henrietta’s Ginger Sign

Ginger House Central Bed Plan

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