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Use warming mats to heat your seeds

Rubberised pads are a cheap, compact alternative to a greenhouse

Greenhouse effect: raising soil temperature using a warming pad. Photograph: Biogreen

Greenhouse effect: raising soil temperature using a warming pad. Photograph: Biogreen

A ll my current fantasies are about greenhouses. I am tortured by emails from fancy manufacturers seducing me with modern glass cubes and cute-as-a-button wooden structures. Imagine standing in a greenhouse, I think, as I play Tetris with seedling trays on countertops at home. What starts off on windowsills quickly sprawls on to any flat surface.

So, for a fraction of the price of a greenhouse, I’ve been trying out BioGreen’s rubberised warming pads as a new solution. You sit the seed trays on flat plastic mats that heat the soil to 5-10 degrees warmer than the ambient temperature. If you stick a bit of recycled polystyrene underneath, and add in some cheap LED grow lights with a timer, you’ve got a pretty good propagation unit.

These warming pads are efficient. I’ve maintained a soil temperature of 22C with no problem, which is perfect for tomatoes, parsley, onions, cabbages, basil, beets, swiss chard… The list goes on; it truly is the sweet spot for speedy germination.

However, there are a few things that like the dial turned up just a bit more: chilli peppers, sweet peppers and aubergines, as well as some of the more tropical herbs, such as holy basil, germinate best between 25-28C. By chance, I found that if you use the sort of insulation board common in roofing – the stuff that’s covered in tin foil – then you can easily bump up that temperature. I’m genuinely excited about this; it’s not easy to find a cheap set-up that will heat that consistently.

You’ll need a propagation lid, preferably with a vent, as the first stage of germination is reliant on moisture, and if the soil around the seed dries out after the initial watering this can be fatal. However, once the seedlings are up, if conditions are too humid, with poor air circulation, you can get damping-off disease – which causes emerging seedlings to collapse, often covered in white mould – and other moulds. That little vent on the top is surprisingly effective. If you do find yourself with damping off, try watering with a strong brew of cold camomile tea, which is naturally antifungal.

Rubberised pads are a cheap, compact alternative to a greenhouse

Influence of heat on seed germination of seven Mediterranean Leguminosae species

Abstract

The influence of high temperatures (dry heat and hot water) on germination of seven Mediterranean Leguminosae species typical of fire-prone ecosystems in southern Spain is analyzed, in order to know the response of seeds to wildfires and the possible implications in their regeneration after this disturbance. Seeds were heated to a range of temperatures (50 °–150 °C) and exposure times (1–60 min) similar to those registered in the upper soil layers during wildfires. Germination tests were carried out in plastic Petri dishes over 60 days. In general, the degree of seed germination promotion by dry heat treatments showed a wide interspecific variation, although the final germination level was increased in all the studied species except for Scorpiurus muricatus. The thermal pretreatment of 50 °C, however, was not effective for germination in any species, and rising the temperature to 70 °C only slightly enhanced the germination in Cytisus patens. The preheatings of 90 °C (5 and 10 min), 120 °C (5 and 10 min), and 150 °C (1 min) were the most effective in promoting seed germination. Hot water (100 °C) scarification also increased the final germination level in all cases, with the exception of C. patens. The germination rates after preheating were much lower than in mechanically scarified seeds and closely resembled those of the untreated seeds, except for C. reverchonii, whose seed germination rate decreased with heat. The response of species to heat shock had no clear relationship with life trait or with the specific post-fire regeneration strategy (obligate seeder or facultative resprouter). Those species coexisting in the same habitats had different heat optimal requirements for seed germination, an strategy suggested by some authors as minimizing interspecific competition in the secondary succession started after fire.

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Department Plant Production & Agricultural Technology, E.T.S.I. Agrónomos, University of Castilla-La Mancha, Campus Universitario s/n, 02071, Albacete, Spain

José M. Herranz, Pablo Ferrandis & Juan J. Martínez-Sánchez

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Herranz, J.M., Ferrandis, P. & Martínez-Sánchez, J.J. Influence of heat on seed germination of seven Mediterranean Leguminosae species. Plant Ecology 136, 95–103 (1998). https://doi.org/10.1023/A:1009702318641

Issue Date : May 1998

  • Hardseedness
  • Heat
  • Leguminosae
  • Seed germination

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The influence of high temperatures (dry heat and hot water) on germination of seven Mediterranean Leguminosae species typical of fire-prone ecosystems in s