How to maintain a herbarium?

I was wondering if any of you mantain a herbarium (I personally do) and I wanted to know:

I had these doubts… and I would like if someone could share their experience…

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I don’t personally keep a herbarium but my office is just down the hall from the one at the university. The room is climate-controlled I think (temperature cooler than usual room temperature and low humidity), so maybe a cool location like a basement room or closet with a dehumidifier running would work for a home setting. The specimens are inside folders kept inside metal cabinets. I’m almost certain those are special airtight cabinets. I’m not sure what else, if anything, is done to prevent mold or pest problems. Also not sure about the labels but they probably use a template of sorts similar to the ones in your pictures.

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You shouldn’t have any mold at all, while pressing them you have to change papers often so no water stays in the plant and then after you set it keep it somewhere with low humidity.
You don’t need fancy template, but download or create and print or just write one with species name, date, location (try to be precise and add gps if possible), name of collector and name of ider, print blank ones and then use pen to sign them with data.

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The classic method in herbariums unfortunately was to use a toxic chemical compound of mercuric chloride to avoid potential insects from feeding on the specimens. However, one of the best botanists in Egypt used to keep his well dried specimens, after being wrapped in a plastic bag, in drawers of his deep freeze for a few hours! This, he informed me, was enough to kill any small unseen larvae or even eggs of insects like silverfish and the like. I never tried this method but I think it is worth a try.
Perhaps spreading some silica sand gel in the box where you keep them can absorb humidity and prevent mould.

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I’m not experienced with herbariums, but it seemed to me that I could help you with the template part and, indeed, it’s not difficult. I used two search engines with the terms “herbarium template” and got some useful-looking results. You’ll need to decide for yourself which fits your needs–or you could create a template of your own (modeled on the best of the ones you’ve come across) using word processing software.

This link has some good information on herbariums in general, so you might want to start there: https://herbarium.duke.edu/resources/resources-for-collectors.

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You shouldn’t have enough moisture to allow mold to grow. As for pests, the idea above of freezing things for awhile seems like it ought to work, and then you’d probably just want to seal your containers well to prevent anything getting back in. Cedar wood involved in things may help a little.

Regarding fungus, as others have said, this is mainly an issue of humidity. Dry the specimens well before storing (an oven at low temperature helps if you’re not lucky enough to live in a desert). Then store in a sealed cabinet with silica gel packs or in a room with a dehumidifier. For other pests, the herbarium I worked in 40 years ago was pioneering the use of microwave treatment to kill any insects and avoid toxic fumigation. This is now a fairly standard technique, but for home use would only be useful for specimens small enough to fit in a home microwave. (We used big scary industrial microwave ovens, without much shielding back in those days.) If you want to try it, just search the web for “herbarium microwave” and you’ll find several articles. Make sure your specimens are dried first, or you might explode the fruits or thick parts.

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Just a couple of tips:

Freezing (of already completely dried specimens) is definitely one of the safest and least destructive methods of pest control, if available to you. The longer and colder, the better. Be sure, however, to use a self-defrosting freezer, and to seal the specimens in a plastic bag before they are removed from the freezer, to prevent direct condensation of moisture on the cold specimens. The bag can be removed after they reach room temperature.

Also be aware that a couple of the methods mentioned, microwaving or using alcohol, will degrade or destroy the DNA content of the specimen (not to mention colors and other properties of the material). If the specimens are only intended for your personal reference, that may not be an issue for you, but could be if you ever wanted to contribute them to an institution later.

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I once visited the herbarium at Lae in Papua New Guinea. They had terrible mold problems because they didn’t have funding to run the air-conditioners, and it is a very hot and humid climate. Every other herbarium I’ve been in has been heavily air-conditioned.

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Thanks guys for the advice! Forgot to detail a few things, so here we are:

  • It’s Winter in the Southern Hemisphere and while it isn’t rainy or foggy every day, the humidity has boosted at least two times more than summer, which may explain why they’re getting bad now and not two months earlier.

@annkatrinrose The room is not really temperature-controlled, but the temperature doesn’t drop or raise too much.

@melodi_96 I change papers once every week, but some appear to be fine (especially most Malvaceae and Capparaceae seem to be fine, the latter looking like it was straight-out of the plant) and the worst ones are Loranthaceae (twice disinfected!) and Vitaceae (I lost two specimens to mold).

@Sunbird Yes, I have a 1995 book that mentions the mercury chloride, but I deducted that if something was toxic but not corrosive, it could get away with killing the mold. Sadly, I’m not sure if the deep freeze can handle a bunch of specimens without them smelling like food (or the freezer smelling like old plants!)

@karen5lund Thanks for the link! The template is just what I needed :)

@fishkeeper the final resting place of the ready specimens is indeed a sealed drawer (not sure if it’s cedarwood, but it’s wood also also you can get true American cedarwood here, but it’s endangered)

@twainwright I did try to use silica gel (we get it a lot here on shoes!) and regarding microwaves, I might try it if the climate keeps on getting worse (which it will) I think only the older might work here, since I have very recent collections that might, as you said, explode.

@jdmore Thanks! As I said before, I’m not really sure if I can deep-freeze them, but it seems like the best option. Might try to do so in the next few days. And mostly I use them for personal research, but maybe I will have to in the future.

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New ones you have to change once a day, if they’re particularly thick you can add more material to those parts so more water is absorbed, they’re done in around aweek if they’re of a weed size.
If you can find a room with good ventilation it will help you too as said by others! Maybe if there’s an oven, etc.

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Be very careful using chemical dehumidifiers and pest control! The Herbarium at our local university (TENN) used to use mothballs. The curator whose office was in the herbarium ended up having to have a liver transplant. They keep the place arctic cold nowadays and nobody has an office in the collection rooms.

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Yesterday I changed some paper so it doesn’t stain. The problem is slightly more controlled than before. Sadly humidity spiked yesterday after a strong rain. Tomorrow I might check with the “grave patients” (and yeah, these plants are my patients now :sweat_smile:)

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