Storage humidity

May 28, 2019

Category: General

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Is there a minimum recommended humidity for summer storage of bulbs?  I had a lot of rot last year so am adding a dehumidifier to my storage room (aka my office.)  Any potential downside?  I don’t know yet how low I can get the room, but is there any advice on what to try for?

19 responses to “Storage humidity”

  1. David Adams, New Zealand says:

    Hello Kathleen,

    I see that you have asked a similar question before. I have searched the archives to find pieces that I have written on previous occasions but can’t find them.

    I rarely get basal rot here. I sun dry my bulbs. I believe that the ultra violet rays of the sun kill the fungal spores. Regardless of how I don’t think that you will get basal rot if your bulbs are fully dry before storage. Jan Pennings backs this up when he states ‘ We sun dry our bulbs.’ Tony James backed it up when he went from losing 500 bulbs a season to basal rot to losing five bulbs in a season, total.

    My advice, forget about a dehumidifier and its associated costs. Forget about chemical dips. Let nature work by getting your bulbs dry and cured immediately after lifting.


  2. Michael Berrigan, Minnesota says:

    Everything on the planet has a thin film of water on it.  Fungus needs mobile available water to sprout and infect your bulbs.  Air dried bulbs have about 40% available moisture.  I do not know of a ready measure for available moisture that is inexpensive.   I can suggest an approximate method:  If you have access to a precise scale, collect 10G of bulb skins form your dry bulbs and then bake them at 225 degrees F for an hour or so.  Lets say they go down to 6 G. The difference of 10G-6G divided by 10G  will give you a percent moisture in the skins.  Soak them for an hour in water, drain and reweigh.  This should give you 100% available moisture.  Lets say  this is 20G  Total moisture would be then 20-6 or 14g.    percent moisture of  your bulbs then would be 4gG /20g-6g or 28%  The initial 10 grams should indicate your water level present in the skins.    The If you reduce the available moisture in the scales of the bulbs below 50% that will inhibit fungal growth completely.  Fungal spores will be able to infect bulbs at 75% available moisture and will grow after sprouting at 50%.  If a breeze is available most bulbs will have their available moisture well below the levels that fungus can attack.


    If the bulbs are small or are in divisions 5 or 6 or 9  Delia Bankhead had a method of placing the dried bulbs in dry sand to prevent them desiccating further.   She devised this for her miniatures.



    My problem is with multiple nose bulbs getting the area between the noses dry.  When digging, I aggressively separate anything that can be separated and have a fan blowing on the bulbs for 3 days turning once.  Bulb losses are minimal if the bulbs are dried right away.

  3. Kathleen Simpson, West Virginia says:

    I do sun dry my bulbs (after hosing off and a brief dip in a bleach solution) and aim for crisp and crackling skins before I move them inside.  Sometimes this involves maneuvering to avoid thunderstorms, but I generally manage.  I think some of the storage rot is caused because we only run the a/c in the afternoon.  Come evening, we open the windows and let the cool (and humid) air in.  Last year was unusually humid (80-90% relative humidity was the norm for over a month) and my bulbs lost their dry crackle pretty early and definitely had more rot.  So this year I plan to keep the windows closed in that room and a dehumidifier running.  (I have been keeping a fan on the bulbs for some years.)

    I was specifically wondering if I could go too far and dessicate the bulbs.  My new unit allows control of 35-60 percent relative humidity, or an uncontrolled constant operation.  I’m  thinking I should set it at 35%.

    Mike, I’ve seen the same problem with multiple nose bulbs.  Do you actually break the plate when separating them?  I assumed that would leave a spot for rot to enter and have not been at all aggressive about pulling them apart.

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

    This is an argument that I have had with some members of the WDS for over 15 years.

    I sun dry my bulbs by digging them and leaving them in the field until they are dry (on the ground).  Rain, shine or whatever.  Before I started doing that I lost as high as 25 percent of my bulbs.  Now I lose 2 or 3 percent, maybe.

    After they dry, I store them in the open under a canvas carport with several racks where the the bulbs are stored in “onion or produce” type bags. They are there all summer until I plant them again. My racks are 4′ x 8′ stacked three high using “chicken” wire as a base so that they get air on both sides.

    Some members of WDS are amazed that my bulbs do well, thank you.  The people that put them under air-conditioning lose more, generally, than I do.

    I go with David Adams that said sun dry, leave them alone for the summer.




  5. David Adams, New Zealand says:

    Further to my previous comment I have always advocated that dipping bulbs after drying is counter productive. Many of my friends used to dry their bulbs, then dip them in fungicide, or bleach, and they ended up with terrible problems with basal rot.

  6. Ian Tyler, England Ian Tyler says:

    I do not wash my bulbs after lifting as the extra water promotes rot, I
    can’t say I sun dry them as I live in the UK but the wind and rain drys and
    washes them with minimal losses.

  7. Kathleen Simpson, West Virginia says:

    Thanks for all the input.  I will divide several clump into test batches this year.  Part will get my usual method, and some will just be sun dried (on the ground, no wash, no bleach) and hung in the tractor shed.

    Assuming it ever quits raining long enough to dig, that is.  Everything on the schedule is extra well marked this year but I still hate digging blind.  No tornados or floods here, though, so we’re better off than much of the US!

  8. Jolene Laughlin, Louisiana Jolene Laughlin says:

    Kathleen – would you mind taking photos and making notes and using this experiment as an article for the Journal? I am very curious about this, especially in areas where it stays humid all summer.

    Thank you!

    Jolene Laughlin, Editor
    The Daffodil Journal

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

    Humid.  You mean humid where the humidity is so high the fish swim through the air. 🙂


  10. Anne Wright, England Anne Wright, England says:

    So, from the above comments: For miniatures, lift and dip then dry thoroughly and store in dry sand? Also, I have problems keeping N. cyclamineus, when I have it, in good condition when lifted for sale. It seems like there’s a tightrope to be walked between preventing dessication or fungal infection. Lift them immediately before dispatching will hopefully solve that one?

  11. David Adams, New Zealand says:


    Malcolm Wheeler has recommended lifting and repotting miniatures as one process. Replant is then in potting mix of similar temperature to that in the original pot. It works amazingly well with few, if any, losses. No bulb storage involved. Again dipping is mentioned and I question its value.

    N cyclamineus is known basically as an annual and needs replacing from seed each year. By nature it self pollinates readily and has heaps of seeds in a pod. A couple of us are lucky though and have found clones that multiply by bulb and have lasted for years.

  12. Jolene Laughlin, Louisiana Jolene Laughlin says:

    Yes, that’s exactly what I mean! Humid enough that clothes take days to dry on a line and get sour in the process; leather mildews in your closet; and chips and bread don’t get stale, they get damp and soggy. And you can’t leave left packets of mints or chewing gum in any of the compartments of your car because they get wet and dissolve into a huge, sticky mess.  
    I don’t know how well bulbs would do “drying” in that environment and am curious to find out if it works. From everything I’ve heard, it’s better to put them right back in the ground down here.

  13. Anne Wright, England Anne Wright, England says:

    I’ve love to do that David, but I sell the bulbs so I can’t repot them straight away. Congratulations on finding a N. cyclamineus ‘keeper’.


  14. David Adams, New Zealand says:

    I sell the bulbs too. The miniatures for sale I throw into a netlon bag and leave them, covered with a bit of rag, on a shelf in the glasshouse and only remove them when packing an order a couple of months later. Again the secret is to keep them dry. Stock and surplus bulbs are repotted immediately. It takes an awful lot to dessicate a bulb, although I have sunburnt the larger bulbs by leaving them in the sun in the paddock for too long.

  15. Anne Wright, England Anne Wright, England says:

    Thanks, Dave. I plan to put mine back in their dry compost once counted until I’m ready to pack.

  16. Naomi Liggett says:


    Sent from my iPad

  17. Clay Higgins, New Jersey Clay Higgins2 says:

    Humidity. In NC where I live, all you have to do is walk outside to feel like you had a hot shower with your clothes on. Working on digging my daffodils, I have showered and changed into dry clothing up to 4 times a day. ( I know. I’m a sissy because I can’t stand eating lunch inside with my “bride” with wet clothes on. I have to go shower, and change into dry clothes.) But that is me. However my daffodils did well stored under the canvas carport all summer, humidity and all.


  18. Jolene Laughlin, Louisiana Jolene Laughlin says:

    Yep! That’s the kind of humidity I’m talking about, Clay. Good to know your bulbs did okay in it. I’ve been leery of trying to store bulbs out of the ground over the summer.

    I learned when I moved here that you can’t store candy or chewing gum anywhere except a fridge in the summer unless you want it to get wet and dissolve into a sticky mess. When chips or bread go “stale,” they get damp and soggy, not dried out and hard. The “born and raised here” folk put rice grains in their salt shakers to absorb the humidity and keep the salt and other spices from turning into a solid clump – most of the restaurants have it in their shakers. And you can’t really dry clothes on the line without them souring b/c it takes days. It’s wet and soggy all the time. Between the early and long-lasting heat and the high humidity, it’s no wonder we’re limited in our daffodil choices.

    Thanks for sharing your experiences and observations!


  19. Clay Higgins, New Jersey Clay Higgins2 says:

    My brother lives in Delhi, LA and he said the humid is just as bad there. He does well with tazetta, jonquils, and bulbocodiums. However, he grows them for entertainment and because he is basically like me, a farmer’s son that can’t help himself but has to dig in the ground. It’s in our blood.J