Washing Seeds

[Cgull49]

In researching how to germinate some of the seed I have received over the years one regularly sees instructions to wash the seed for 7 days in water, or wash the seed for 5 days in soapy water, or wash the seed for 14 days with 3% Peroxide. The list goes on.  My question is has anyone done any research to see whether it is possible to shorten the time to wash these seeds without negating the benefit of washing them at all.

Is the instruction to wash the seed for 7 days given because the expectation is that you're busy and only have time to wash them once a day or they need to dry after you've washed them and we all live in damp climates where it will take a day to dry or is there some chemical process happening that it initiated by the washing that if interrupted sooner by washing again will prevent the seed from germinating.

What would happen if I washed the seed 4 times in one day and 3 the next?  Would that meet the requirement to wash them 7 times? And would they then germinate as if I had washed them 7 times over 7 days?

Rob

 

[David Nicholson]

I can see what you are getting at Rob and it is a puzzle. The only seeds I grow that I feel the need to soak are:-

1) Irises: because I have read that nature provides the seed coats with a germination inhibitor and soaking them for 5-7 days in tepid (well to start with anyway!) water with the barest dash of washing up detergent, changed on a daily basis helps to remove the inhibitor. Sometimes I have thought this has worked and sometimes I have thought that germination was just as quick if I simply sowed them and put them outside to the weather. My trouble is I am not methodical enough to keep proper records to justify soak or not soak.

2) Crocuses: when the seed is more than a year old just to plump them up a bit.

3) Cyclamen: nearly always, unless I think "oh, sod it" and don't bother. Again, if I was methodical I could probably justify my actions either way.

Not sure that any of this helpful to you in any way though

[Sinchets]

I always think that if you get enough rain in autumn or spring- or water from snow melt and the seeds are sown outside then there is probably little need to wash them- unless you have the spare time on your hands.
Nature does a pretty good job here of germinating Iris for me and other species which are said to require washing.

[Rodger Whitlock]

Keep in mind what the purposes of the process are.

To my knowledge, there are three purposes to soaking (not "washing") seeds before sowing:

• Fully and evenly rehydrate desiccated seeds.
• Leach out growth inhibitors.
• Remove seed-borne pathogens, primarily fungi.

On this subject, there is more than a whiff of the logical mistake "post hoc, ergo propter hoc". Just because a certain treatment led to success doesn't mean the treatment caused the success.

My point of view, based in part on experience, part on hallucinatory delusions:

• Rehydration of most seeds is accomplished within 72 hours' soaking.
• Few seeds have significant growth inhibitors, but those that do, notably Glaucidium palmatum, may benefit from soaking in repeated changes of water for up to two weeks, perhaps longer.
• Superficial sterilization with peroxide or hypochlorite takes only a few seconds or minutes.

Ergo and therefore, it seems to me that the simplest recipe is to soak all seeds in water with a drop of wetting agent (dishwashing liquid) for 72 hours. Ordinary Sunlight liquid, without anti-bacterial agents, is a good choice in Canada. In the US, Ivory Dawn is a good choice.

Certain seeds require a much longer soak. I don't know of an example other than Glaucidium, but there are sure to be some.

Finally, give all seeds a short (ca 15 minutes, perhaps much shorter) soak in dilute peroxide just before giving them their last rinse and sowing them.

But there are other things you can do to improve germination. Sterilize your soil, or at least pour boiling water onto each potful before sowing. And if you can find a good general fungicide, an application may do wonders. I have been told that an application of Captan WP to seed pots greatly improves germination percentages. Unfortunately, Captan seems to be off the market because of suspected carcinogenicity.

[Lesley Cox]

Daphne is thought to have germinating inhibitors in/on their coat. Someone I read about somewhere (maybe Alpine-L or the Old Forum?) put the seeds in a little muslin bag and hung it inside the lavatory tank for a week or some days. Apparently that worked a treat.

Regarding fungicide onto the seed pot (or through the compost Rodger, or watered on, at or before or after sowing?) I have been told that some fungicides themselves inhibit germination, Benlate being one, but not the only one.

[Cgull49]

Interesting feedback.  I almost always soak cyclamen seed before sowing and have been pretty successful in getting them to germinate.  I also agree that I could put my seed pots outside where they would experience normal rain and in time germinate, however  I have lost lots of pots of seeds when we got a very heavy rain that caused the seeds to be washed away.

However, I guess I'm a little impatient and I want my sown seeds to germinate as quickly as possible even if that takes a couple of years - impatience is a relative thing.  As a result I will wash Arisaema, Daphne, Polygonatum,... before I sow them, which brings me back to my initial question of how the instructions to wash certain seed a number of times over a set number of days was established.

If you have managed to get a copy of Deno's Seed Germination study, you will notice that he recommends that some seeds such as Arisaema, Daphne,... are washed and this recommendation will vary depending on the species. Unfortunately, he doesn't say how he determined the washing criteria. Maybe Kristl can shed some light on this topic.

[Sinchets]

Interesting, I have never soaked seed of Daphne, Arisaema or Cyclamen and have never had a problem germinating them. Maybe I have always been lucky to have 'special rain' wherever I have lived and sown them.

[Ezeiza]

Arisaemas germinate a lot better with lots of rainfall/watering suggesting their inhibitors take time to be rinsed away.

Another group that needs lots of watering is that of summer rainfall South African and African plants.

This suggests that a previous soaking will help wash part of the inhibitors but Brian Mathew suggest changing the water several times.

Of course the seed can not be left submerged for a very long period or it will rot.

[Sinchets]

That's why i cannot think there would be a problem if you are sowing the seeds and leaving them exposed- as appropriate- to winter melt water or spring/ autumn rains. You are only going to need to fuss with soaking if you are sowing/ growing undercover, indoors or in jiffy bags 

[Lori S.]

As a result I will wash Arisaema, Daphne, Polygonatum,... before I sow them, which brings me back to my initial question of how the instructions to wash certain seed a number of times over a set number of days was established.

If you have managed to get a copy of Deno's Seed Germination study, you will notice that he recommends that some seeds such as Arisaema, Daphne,... are washed and this recommendation will vary depending on the species. Unfortunately, he doesn't say how he determined the washing criteria. Maybe Kristl can shed some light on this topic.

Rob, I can't find any recommendations for washing Daphne seeds in Deno's 3 seed germination publications... ?  (Arisaema, yes.)  If you refer to the first publication and the first supplement, he shows his data for a few Daphne species - generally (if it's possible to generalize and it may not be) germination occurred in a 40 -70 pattern, and GA-3 is effective on some species.  It doesn't seem to be Deno who is recommending washing Daphne, at any rate.

Chapter 8 in the first publication (on seeds in fruit) says that experiments were done with cleaning/washing done for 7 days and for 4 weeks, in order to find out whether the previous washing experiments that yielded unclear results were perhaps not done for long enough.  Deno had to establish consistent methods for scientific validity (e.g.  other standards - 70 deg F, 40 deg F, 3 month periods) so that may explain the origin of "7 days".  He found it was effective, and it also became the standard for his consistent testing.  There is also discussion on how adding detergent to the rinse water is effective for some fruits with oily flesh.

Something I always wonder about is the common practice of soaking (as opposed to washing) seeds, in light of Deno's findings.    In his 1st supplement, he comes out pretty strongly against it, based on his observations.  He starts by saying he did not find it to be more effective at speeding germination than his regular treatment in a moist paper towel.  Then he goes on to say:  

"More alarming is the fact that many seeds die at a significant rates(sic) under water even if the water is changed every day and even if the seeds are only under an inch of water.  What happens is that many seeds and particularly large seeds commence a rapid metabolism on moistening which has a large demand for oxygen.  If placed under water the delivery of the oxygen to the seed is inhibited, and the seeds start to die of asphyxiation."  (pg. 11, First Supplement to the Second Edition of Seed Germination Theory and Practice, Norman C. Deno)

[Kristl Walek]

I am extremely careful with soaking seed---overnight is done---usually a GA-3 soak; and with hard-coated seeds, just to see which ones will take up water in that period of time (have a passage to embryo) so that I am relieved of scarification (very difficult with arthritic fingers).

Other than that I have experienced the down side of doing it for longer periods.

And of course soaking is not washing. The washing, as has been said, is normally related to germination inhibitors (most often present in seed of berries/fruited species, though not always). I think of Viburnum in particular, where the wash seems to make a huge difference (my own experience and oft related by my customers who have followed my instructions to do so). Even when the seed is initially cleaned/washed by me before it is sent out, inhibitors still remain.

Rob, if you can manage the recommended washing in one day---thats fine. If refers more to the number of washings, rather than any time period.

[gote]

I have had no problem with unwashed Glaucidium palmatum.
I just sow as soon as ripe. However, since they ripe very late in my place, I do not expect them to sprout until spring anyway and they have had ample amounts of moisture during the winter some of the moisture no doubt moved in the soil.

Malmgren has reported, that sterilization of orchid seed (terrestial) is necessary for good germination. The inference seems to be that the sterilization turned off/removed inhibitors or damaged the seed coat. He has been using sodium hypochlorite. 0.3% to 1% 5 minutes to 45 minutes depending upon the species. Sometimes also diluted sulphuric acid as well.
In these cases he is NOT using any fungi for germination.
An alternative (used by others) is to sow on a growing fungal colony of the right species.
My personal inference is that, in nature, the seed coat inhibits germination until a fungus starts to destroy the sead coat.

Göte