Breaking Seed Dormancy
Getting seeds to germinate can be as simple as showing them some soil and moisture, waiting for a couple of days and seeing fresh green sprouts. But not all seeds are this easy. Many seeds in the Protea family, for example, have specific needs that have to be met to break their dormancy. This includes subjecting them to smoke. Others require scarification, or having the outer coating of the seed removed. Some want to be soaked in water. The list of special treatments is almost endless, with many seeds requiring more than one type of treatment.
You may be wondering why I am writing about seeds and germination right before winter sets in and not in spring. Well, many of the plants that interest me do sprout in the fall. This gives them the best chance to get established over mild winters, put on a lot of growth in spring and then prepare for the harshness of summer. Plants need to have built up a good strong root system if they are going to survive months without appreciable water during the summer drought.
I have acquired a couple of seeds recently where there are no serious suggestions for germination. One offered – we don’t know how to break their dormancy, so we suggest you buy thousands of seed in the hope that one or two may do something, sometime. They also added that it may take a few years. Another seed had the suggestion that putting it in Emu dung may help. Fat chance of me finding much Emu dung laying around in Oregon!
In both of these cases, it is not that they would be problematic in the wild. Seeds have dormancy triggers for very specific reasons. They make sure that when they do germinate, they have the best possible chance of survival. Perhaps Emu dung is a good idea. Perhaps it indicates to the seed that it has a supply of food, and that there is something specific about Emu dung that sends a chemical trigger. There are some seeds that require a particular animal or bird to have eaten it. As it passes through their digestive system, the acid probably gets rid of the outer coating and it is delivered with a food source.
Many times, we don’t understand the triggers, or have to find ways to make the seed think it has been eaten. For many years, it was thought that the Proteas needed fire, only to learn that it was in fact chemicals from smoke that triggered them. People are still not certain what chemical it is, and different plants do want smoke from different things being burned.
When starting plants from seeds, these are some of the challenges that we face. We basically have to conduct small experiments to try and find out what works and what doesn’t. Whenever I try seeds that are new to me, I tend to divide them up into several batches. This assumes I have enough seed. Then I can do things slightly differently for each, such as putting some of them on bottom heat or not. I may subject some to wider temperature swings by leaving them outside.
There are some other tricks that you learn along the way. For example, if a seed has a shiny, tough coat, it will not absorb water and thus the chance of success is very low in the short term. It is possible that if left long enough, that coating will break down, but that could take years. So, scarification can help. I have also been using hydrogen peroxide treatments more recently. It can really soften up a hard coating. A 1% solution for 24 hours seems to do the trick.
Another trick, especially for seeds that I expect to be slow in germination, is the use of fungicides. I have been trying two different techniques. The first is to dust the seeds in a powdered fungicide. The second is to water the plants in a liquid fungicide. The former is better when first planting the seeds. The latter really helps stop the onset of liverworts when germination takes a long time or the seeds are under mist.
Both techniques are helping. I would often see dark patches forming in my nursery pots where a seed had been. Those had basically been attacked by mold. There is a lot less of that now. Results of my germination experiments will be included on the plant pages going forward, but not all of my previous attempts were properly documented.