Heat Packs

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Ray

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I didn't want to hijack the OZ thread, so am starting this one.

Heat packs are a mixed blessing....I have gotten plants that were severely burnt from their proximity to the heatpack. In my entire ordering history over the past few decades, I have only once gotten plants that were killed by freezing, regardless of heatpacks.

The term "heatpack" is not a universal descriptor. They vary all over the map.

The best ones I have found are Uni-Heat 72 + hour packs. If kept at room temperature, they will heat to about 115°F surface temperature in about 4 hours, then degrade to about 100° over their usable life. However, temperature is not the key, heat output is, and one of those will boost a 1 cubic foot box about 10°-15° over ambient, so you have to use the appropriate number of them. Then there is knowing how to use them.

Some put them right up against the plant, but they are intended to heat the enclosed environment, not the objects in it. If it wouldn't mean so much work, ideally one would affix one smaller pack on each wall of a box. Instead, if you place one, two, or a few strategically around the box, and insulate the box - I use a closed-cell foam, but newspaper is great, too - you can have a nice cozy environment for the plants. I have successfully shipped blooming plants to Alaska in February using them.

Even though they appear to be mesh bags of powder, there really are only a relatively few perforations in the enclosure to allow oxygen and humidity in. If you cover those (they are usually marked with a colored stripe), they won't work properly. The same is true if you do an absolutely excellent job of sealing the box.

The basic concept is iron filings and salt in a bag. Moisture and humidity entering the powder causes the iron to rust, which is an exothermic reaction. If you starve the heatpack for either, the process slows. I prefer not to ship in winter with wet potting media, so I'll throw a wet paper towel in the box.
 
Thanks for sharing your knowledge and experience, Ray. If most businesses shipping plants shared your understanding I'm sure the results would be more satisfying. I have to echo Eric's experiences.

I have seen many more plants damaged, or just plain cooked, by heat packs than damaged by cold when shipped in cold weather. Plants do not freeze with routiine good handling by the post office or major shipping companies. Plants freeze when weather delays them in transit, when trucks break down, or when delivery personnel leave them outside in sub-freezing temperatures.

Find out which delivery option gives the most reliable service in your area, work with a vendor that will check for truly extreme weather conditions and potential delays before shipping, and skip the heat packs. And avoid the holiday shipping season. I don't hesitate to have plants shipped to me in Madison Wisconsin in winter if I can do those things.
 
When I ship plants in winter, I use the carrier service guide. If ground is within 2 days, I'll use that. If not, I go with 2-day service.
 
I have only ever received one shipment with a heat pack. It came from Sam, shipped from Montreal in October. Temperatures were mild; so, no heatpack was even required. It was placed right up against my bundle of Paph lowii seedlings. The one closest was cooked. The next was badly damaged and died later. The other 3 were okay.

I have also received shipments in the cold winter months with no problems and with no heat packs. I have the shipper deliver my order to a FedEx shipping depot, not just a drop box. I have it shipped to me, "care of" a conveniently located FedEx depot near me and then "held for pick-up". The hold for pick-up service is available at the major depot locations. I also have the shipment sent with air-overnight delivery service to keep it moving and not sitting in a cold truck or a temporary storage area. I've never had any problems when using this method.
 

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