J Kolenovsky wrote:

.(I got into something really neat this year in the early spring with
pre-emergent control - a propane torch,
http://www.flameeng.com/. Works really well)


Not exactly a pre-emergent control. You have to have some leaves to
burn. Unless you really toast the soil, the torch heat doesn't penetrate
much soil. However, it's really a useful tool in the garden. And it
appeals to male gardeners a lot.

I use one for growing carrots. I make a seedbed, water it and let the
weeds start growing. When they're 1/2 to 1" high, I burn them. You don't
have to really toast the plants: that wastes fuel. All that is necessary
is to raise the temperature of the leaf surface sufficiently to boil the
fluids, breaking the cell walls. The leaf then dies and takes the plant
with it. With the Flame Engineering Red Dragon torch, walking down the
row at a moderate saunter is enough. The range of the torch is less than
a foot across the bed and less than 1/8 inch into the soil. If the weeds
are more than 2" high you have to toast them more. Get them early.

Back to carrots: after about 2 weeks killing weeds I have a stale
seedbed (the weed seeds near the surface have germinated and I have
killed them so there are not many more weeds that are going to grow.) I
then plant carrot seed, about 1/2 inch deep, trying to minimize soil
disturbance (which brings up more weed seeds). After about 5 days I
torch whatever's up. On the 6th day the carrots are up and the bed is
fairly weed free. I have noticed carrots emerging as early as 6 hours
after the last flaming, but usually my timing is not that good. Since
the carrots have to have germinated by that last flaming I infer that
the torch does not reach significantly below the surface, otherwise I
would have toasted my carrots.

If you try to do this take note: it works poorly in the spring since
weed seeds germinate at different times and many wait until late spring
or early summer so you won't have toasted them with the torch. Best time
to use it is late spring or later. It also works poorly on grasses,
since the growing point is underground and the torch doesn't kill it.
Works great on broadleafed weeds. Note further that you really have to
water the weeds to get them to germinate so you can kill them. If you
don't do this you don't get control. It's really tricky to use the torch
when there's a crop in place. Expect to lose some of the crop if you try
this. A small pebble can disturb the flame enough to throw heat back
onto the crop and damage it.

You used to be able to get 6 lb propane cylinders before they came out
with the consumer-proof devices they now have added to the tanks. They
were much easier to put on a backpack for garden work. Haven't seen them
recently.