Bill Carter, Washington

Hot Water Treatment – HWT

June 10, 2013

Category: Diseases and Pests

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I thought I’d repost an email I got from Bob Spotts on Hot Water Treating

The only question I still have is should I do the hot water treating just after I dig the bulbs or just prior to planting this fall?   It seems there are two lines of thought and who knows maybe it does not matter.



Here’s my simple-minded way of HWT.

I use a camp cooler like you propose. I don’t heat water, I use water from my house hot-water heater – it has a faucet near the base. I set the hot water heater’s thermostat well above 120F. I take about 2-3 gallons out in a  5-gallon pail and pour it into the cooler. I add peracetic accis (a few ounces to give about a 0.5% solution) – this is my fungicide/nemacide. I use a digital thermometer (one with a sensor at the end of a wire) to determine the water temperature. When the water temperature is about 115-116 F, I add the bulbs (in mesh bags by seedling and scrubbed/ jet-sprayed with water) and close the lid. The water temperature drops and I take more water from the hot water heater and add to bring the temperature to about 114F. The bulbs absorb the heat and the temp  continues to slide down. When it drops to about 110 (just a few minutes), I again add enough hot water to stabilize at 113F. After that, I add enough hot water every 45-60 minutes to maintain 112.5-113F. I soak for 3.5 hours.

I HWT bulbs immediately after lifting.

I HWT all bulbs I intend to replant. Discards to be given to others sometimes don’t get HWT. Depends on where they were growing and the amount of losses encountered there.

Bulbs don’t absorb heat from the air (ie, greenhouse) nearly as rapidly as from a liquid. I don’t think heating in a greenhouse will work. Ian Tyler has experimented with microwaving bulbs. Give him an email.



2 responses to “Hot Water Treatment – HWT”

  1. Jason Delaney, Missouri Jason Delaney, Missouri says:


    I am digging bulbs now, and I will HWT in late July, at 112F for 4 hours in tanks made from extra large chest-style freezers, with recirculating sump pumps and a hard-wired,  30-gallon electric hot water heater.  I’ll add 600 ppm chlorine to  to each batch, as well.  Heating the water takes the longest, but but stave wasting time, while one batch cooks, you simply heat up the water in the second freezer, so there is always something going on.   Easy as pie, really.  I can treat about 750 large, multiple-nosed bulbs per batch while maintaining constant heat and agitation in the water–the key is a good electronic thermometer and a newer (<15 year old) freezer that was EnergyStar-rated, for maximum insulation.   Last year we were able to keep water in one freezer at a constant 98F overnight, with only the lid shut.  And, the newer freezers weigh very little, so they are easily moved around and cleaned out, and stored away.

    Last year I HWTed at the end of August, and the foliage on the plants was significantly more spotted and contorted than it should have been; there was also more bulb division this spring, likely as a result of damaged meristem tissue from the heat (and possibly the high concentration of chlorine).   Yet the flowers were, largely, absolutely normal, which really surprised me; overall, the plants were steroidally HUGE, bigger and more lush than I have seen them, so I was quite pleased.   Most growers I discussed this with at length suggested doing it sooner than later, but to let the bulbs harden off after digging before treating; too soon and the bulbs are vulnerable to greater damage as their tissue is still succulent, and waiting too late in the season may cause significant damage to the following year’s growth, which by planting time has already formed within the bulb.

    A great book discussing this treatment is  I highly recommend it.

    Good luck,



  2. Clay Higgins, New Jersey Clay Higgins, North Carolina says:

    Jason and Bill,

    Here is something to think about.  I have done a lot of study of HWT because of nematodes and have successfully kept them at bay for a long time.  This comment is limited to HWT for nematodes and not for basal rot or other reasons.

    According to the books, nematodes go inactive in the hot weather, so HWT treatment late is recommended that the bulbs be soaked overnight in cool water to “wake” up the nematodes so that they will most likely be killed by the HWT.  Treating the bulbs with HWT early while they are still active may be a way of controlling them also.  I have never tried that.

    I usually treat my bulbs around the early part of September.  It doesn’t seem to do any damage and the bulbs come up and bloom nicely the following year. I use the same method that Jason uses except that I use a “used” lab incubator.   I, however, am being constantly being told that my blooms are on a stem that is too long.  Is it the HWT?  I don’t know.