Traditional Hugels are not suited to all plants.
- Trees or shrubs over 1m tall. The hugel will not provide enough stability for the root system and they may blow over. Also a concern is that the heat of the decaying wood might burn the tree roots. Use a hugel stack approach instead.
- Potatoes or other invasive tubers such as sunchoke(jerusalem artichoke), new zealand yams, etc. These will penetrate into your stick and wood layers and you will have to dismantle the hugel to harvest or remove tubers. Use a sunken hugel, or dedicated potato bed (which is what I do).
- Garlic, onions, parsnip and carrots grow happily, but the coarse material close to the surface of the hugel can create crooked tubers and prevent garlic and onions from bulbing correctly. Plant in sunken hugels, or manage hugel construction (and maintenance) to accommodate their specific needs.
- Celery and leeks require blanching, and therefore a much deeper trench than you will normally create with your hugel. I find that because of the steep shape, I can only maintain 10-15cm of compost on the sides and top of the hugel. Most plants are happy to grow down into the sticks and coarser material, but this can be a challenge for celery and leeks. I plant these in pots adjacent to my hugels.
Although a tradtional or hybrid hugel increases the growing area of your garden, different sections of a hugel are not identical.
I divide each of my hugels into three zones:
- Sunny side: good suntrap for longer maturing plants (such as cabbages and cauliflower). The base of the hugel provides better root stability for tall plants (such as eggplant and capsicum), and better water retention.
- Plateau: dryer, but deeper growing medium, better for root vegetables like carrots, beets and parsnip.
- Shady side: low growing plants will be shaded by plants on the top of the hugel. Good for protecting heat sensitive plants such as lettuce, dill, coriander, etc. In the middle of summer and with the sun directly overhead, the shady side gets plenty of good sun. The base of the hugel provides better root stability for tall plants (such as corn and tomatoes), and better water retention.