Hi all, I just posted this on different site in response to someone. It seems to work, but frankly i know stuff all about cactus seed raising. But its cheap ...mine didn't cost anything
fwiw I'm new to cactus seed growing and i didn't have a heat mat. So about a month ago i devised i this fish tank heater method:
I got a rectangular plastic container (roughly 450 x 300mm) and put about 30 - 40 mm of water in it. Into that i put the fish tank heater set on 25C or whatever. Then I just plunked the seed tubs (take away containers) into the heated water 'bath'. The water level rose to about 60 mm. The weight of the sand inside the tubs stopped them from floating off.
The thermostat in the heater keeps the water temperature steady. And because the the tubs are surrounded by water the wet mix inside them is kept at the same temperature as the water.
I was concerned that there could be a hot-spot near the heater. But when i checked with a thermometer this wasn't the case. In fact the water seemed to heat surprisingly uniformly, even when the container was full of seed tubs (12). I guess the water mixes through convection. Often the heater is touching the plastic tubs etc, but there's never a problem, the water absorbs the heat.
The temperature of mixture in the pots took about 45min or so to stabilize at the water temperature. This was with closed seed tubs, open ones had a T about 1C lower than the water.
Its cheap and gives me very good control over the temperature in the seed tubs. The temp in the tubs is uniform...( I obsessively measured it over 2days b4 risking my precious new seeds!). Ive used cups and bags in it too...seems to work the same.
Like I said I'm new to this, and i only made this a month ago, but it seems to work a treat. I grew my first cactus seeds -lophos - and they mainly sprouted in about 9 - 14 d and stacks of trichs which germed in about 4-5d.
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My computer got zapped by lightening the other day so i may not be able to reply very promptly to anyone for a coupla daze.
I read the other day that sempervivums protect against lightening AND evil spirits. Reckon i could use a few round here.