To soak or not to soak, that is the question Hamlet would have asked if he liked growing peas. Lots of people recommend soaking peas before planting, but does it do any good? Will soaking peas speed up germination? Will it produce fruits sooner?
Dry pea seed is extremely wrinkled and soaking in water plumps them right up. It is also known that seeds need to absorb water before the germination process can start. Soaking peas before planting makes perfect sense but what happens in the garden. Is there really a benefit to soaking?
Why Does Soaking Peas Matter?
Most varieties of peas are ready for harvest in 60 days from planting. They will continue producing fruit until temperatures get above 30°C (85°F). They also won’t grow below 4°C (40°F), so in many climates they have a short growing season. If this could be extended with quicker germination, gardeners can expect a higher yield.
Pea Seed Germination
All seed dries as it matures and gets older. In some cases the drying process actually kills the seed, but in most cases it helps the seed survive for a long time. As pea seeds dry, they loose a lot of water and start to shrivel up and look wrinkled.
Interestingly, not all peas get wrinkled. Mendel noticed that some peas were wrinkled and others were smooth and this led him to some interesting genetic findings.
This drying process puts the seed into dormancy; a kind of hibernation. As seed absorbs water, the water triggers a series of chemical reactions that eventually lead to germination. Slow absorption of water slows down the process and faster absorption speeds it up.
If water is absorbed too fast, it can actually damage the seed and prevent germination and this is not a well known fact.
Can Peas Be Soaked Too Much?
How long should you soak peas? Most recommendations suggest anything from 4 hours to 48 hours. An overnight soak is very common.
A 24 hour soak is enough to take out most wrinkles. More than 48 hours can harm seeds.
The easiest way to soak peas is to put them in a small dish, and cover them with tap water.
The Rationale For Soaking Peas
When peas are planted without soaking, they must get the moisture from the soil. After planting there will be air spaces around the seed and only part of it will touch the soil. Water can only be absorbed at the points where the seed makes contact with soil, and therefore the natural process in soil is slower than placing the seed in water.
In theory at least, this should slow down the germination process.
What Does the Science Say?
I thought there would be quite a bit of testing on this, but it turns out soaked peas are too difficult to sow mechanically, so it is little interest to agriculture, which means that people with funding, don’t care.
An old study from around 1920 found that for both beans (red dwarf beans (Phaseolus vulgaris) and peas (Button’s “Maincrop”), soaking for periods of 24 to 48 hours increased the rate and vigor of germination, but that subsequent development of seedlings was harmed. For peas, after 3 weeks, 72% were alive without a soak, and only 40% with a 48 hour soak. A 72 hour soak reduced this number to 28%.
That is the only study I found.
What Do the Experts Say?
West Coast Seeds suggests not soaking in “damp soil”, but gives no suggestion for dry soil. Michigan State University recommends “Soak seeds for 24 hours to hasten germination“. University of Minnesota Extension does not mention soaking but does says, “good growing temperatures for peas are between 13°C (55°F) and 18°C (65°F)“.
Recommendations are mixed. Some say soak, some don’t.
Do Soaked Peas Germinate Faster?
I compared three treatments; dry seed (A), seed that was placed on moist paper towel (B) and seed that was covered with water (C). After 24 hours, the seed on moist paper had swollen a bit but was still showed wrinkles and there was no sign of root development. The soaked seed was wrinkle-free, larger and you could clearly see the root developing under the seed coat.
At this point in the experiment, the soaked seed was also put on moist paper towels, which is a standard way for labs to check seed germination.
After 72 hours the seeds that had been sitting on paper towel (B) show signs of the root expanding inside the seed coat, and the soaked seed have developed significant roots.
Clearly, soaking speeds up germination when compared to seed that has limited exposure to water.
How Quickly Do Peas Absorb Water?
As I was writing this post it occurred to me that we “assume” pea seeds absorb water more slowly from soil than when they are submersed in water, but is this really true?
I took some dry pea seeds and dropped them in some water at room temperature – exactly what I would do in spring before planting. I also took some dry seeds and planted them outside. I placed them about an inch deep, and watered them in. It was mid November (fall here), but we had a week long cold spell with heavy frost and snow. At planting time it had warmed a bit to 6°C (43°F). The soil was cold, no longer frozen and not unlike soil at spring planting.
After 24 hours, the peas soaked in water had swollen quite a bit and had almost no wrinkles. The seed in the ground was dug up, cleaned, photographed and buried again. These seeds had expanded quite a bit compared to the dry seeds but were not as large as the soaked ones and they still showed some wrinkling.
The peas in soil were again dug up after 48 hours. They are now about the same size as the ones soaked in water and the radicle can just be made out below the seed coat. The roots of two of the soaked seeds have broken through the coat.
After 72 hours, the peas in soil were unchanged and no roots had emerged. The soaked seeds had longer roots.
Seeds in soil absorb water fairly quickly – much faster than I expected. The soaked seeds did germinate faster, but in this experiment they were also kept warmer.
I wonder how far ahead the soaked seeds would be if they were soaked for 24 hours and then placed outside in cold soil? Unfortunately, it has gotten too cold here to do this experiment now.
Do Soaked Peas Grow Faster?
All this talk about faster germination is interesting, but what gardeners really want is earlier peas.
Last spring at pea planting time, I made up three pots using my garden soil. I planted 5 dry seeds in one and placed the remaining 10 seeds in water. The next day I planted another 5 seeds in the second pot (24 hr soaked seeds). After 48 hours the remaining seeds went into the third pot.
After growing them for several weeks, the tallest seedlings in all three pots were about the same height.
There was little or no difference in root growth in the three pots.
You can get more detail on this experiment in this video, but in conclusion, soaking did not produce faster growing plants.
If the above video does not play try this link: https://youtu.be/vJxMAwSc6ms
Does Degree of Dryness Have an Effect?
A study using 12 soybean varieties found that soaking beans cold (5C), that had a moisture content of only 6% resulted in slower growth and higher mortality, although soaking warm (25C) had no such effects. A moisture content of 16% was unaffected by by cold or warm soaking.
Moisture content for safe storing of peas is 14%.
If you are going to soak seeds, soak them warm. This study also suggests that increasing the moisture content slightly before planting may also have an advantage.
Dry Soil vs Wet Soil
The reference above from West Coast Seeds was the only one I found that mentioned wet soil. It is quite possible that peas have difficulty getting enough moisture in dry sandy soil and then soaking might have a much greater effect.
Soaking Peas Before Planting – Does It Improve Germination?
Soaking pea seeds does speed up germination a bit, but in my tests it did not produce larger plants, which probably means the harvest will not be any quicker.
Provided your soil is wet, or you water regularly, there seems to be very little value in soaking pea seeds before planting.
Extended soaks of more than 24 hours should be avoided, because they can harm seed.
Unless new evidence surfaces, I’ll skip the soak and plant dry.
If you want earlier crops, it’s probably more beneficial to find ways to warm up the soil in spring so that seeds germinate and grow faster. This could easily add a week to the season, whereas soaking adds at most a few hours.