You might think this post on potato/green sprouting is too early since it’s just a few days after Christmas. But if you want a lot more yield from your potatoes even if your space is limited, give it a read so you’ll have time to think about what you want to do. You might need to order a bit earlier than usual to take full advantage of this information.
Jim Gerritsen – One of the Foremost Potato Growers in the US Today.
Jim Gerritsen has been farming organically for 39 years on his farm (Wood Prairie Farm) in northern Maine. He was organic long before organic was fashionable and is one of the foremost potato growers in the country today. Well known and active in the organic community, Gerritsen is probably best known as President of the Organic Seed Growers and Trade Association. (See my post Monsanto-Goliath-Challenged by David/.)
I had the good fortune the other week to find out about a webinar that Jim was offering on growing potatoes. The very first thing he covered in the webinar was green sprouting. And in all the years I’ve gardened, I’ve never had the in depth understanding that Jim gave me in the brief time he talked in detail about the why and wherefores of green sprouting. (Known as chitting in Europe).
An Optional Process
Understand that green sprouting is not something you “have” to do to grow potatoes. It’s a preconditioning step (in 2 stages) that’s optional. But this leading potato grower set forth some pretty compelling reasons to take the time to green sprout.
The main crop that Wood Prairie Farm produces is seed potatoes. They plant 25,000 lbs of seed potatoes per year! And they green sprout all of them.
Their farm is in northern Maine only 6 miles from Canada. The growing season is a short one.
- Green sprouting knocks 10 to 14 days off the growth cycle in the field.
This could make a big difference for a gardener/farmer who sells at a farmer’s market. They’d have potatoes for customers almost 2 weeks sooner than their competition. This might be enough in itself to gain the loyalty of those customers for the entire season.
- Taking off 10 to 14 days of the 11 week growth cycle enables the Gerritsens to grow some of the late season varieties that they would not otherwise be able to grow because of the short season. In turn, growing these late season varieties enables them to supply folks in the south who have longer growing season.
- If potatoes are stressed in August from drought, excess rain, heavy pressure from pests like Colorado potato beetles or leaf hoppers, or maybe weeds that are out of control because of rainy conditions in the spring, the potatoes are still 2 weeks earlier in their development than they would be without green sprouting. They can better handle the stress since they’re further along. Jim said this can make a big difference in yield.
- One of the most appealing benefits of green sprouting for most gardeners/farmers is increased yield. If you green sprout properly (I’ll get to the “how to’s” in a minute) you’ll have more potatoes.
What Happens Without Green Sprouting
Without green sprouting there tends to be only one dominant sprout (also called a king sprout, primary sprout, or apical sprout) that grows and sets potatoes .
What Happens with Green Sprouting
Green sprouting will suppress the dominance of that one king sprout and enable secondary sprouts to grow. Sprouts become stems and that’s where potatoes are set.
Thus, more potatoes will be set. The highest yield comes from having the highest set (or highest number of potatoes/tubers).
In other words, increasing the sprouts will increase the stems, which will increase the set, which will lay the foundation for increased yield. (You still need fertile soil and adequate moisture of course.)
Adequate Moisture and Green Sprouting
Tuber set occurs approximately 4 weeks after plant growth emerges from the ground.
Adequate moisture at the time of tuber set will help the plants to set a higher number of tubers/potatoes.
It was pointed out that in Maine they’ll have an early dry period about 2 years out of 10 in the spring/summer when tuber set occurs. That’s also true here in Virginia. Green sprouting in those years will encourage higher tuber set in spite of the dry weather.
WHEN to Start the Process of Green Sprouting
Green sprouting should start 4 weeks before your intended planting date. There are two stages.
STAGE 1 – Warming the seed for a week to 10 days to break dormancy.
Be aware that some varieties will break dormancy in a week. Others like Swedish Peanut and Red Cloud may take 10 days or more.
VERY IMPORTANT: Potato seed should be warmed at temperatures between 65ºF and 75ºF for a week to 10 days in the DARK.
By sprouting at these temperatures, you are suppressing apical dominance.
What is Apical Dominance?
The apical end of the potato is opposite the stem end that grows above ground. That apical end tends to have a concentration of eyes. When left to its own the primary or king sprout will grow and dominate the secondary sprouts.
The king sprout (apical, primary) might set one or two tubers.
By keeping potatoes in the dark at these higher temperatures (65ºF to 75ºF) which suppresses the dominance of the apical or king sprout, more eyes will sprout and thus more stems are formed, and then more tubers.
How to Tell When the Potato Has Broken Dormancy
When the eyes begin to sprout the potato has broken dormancy. They’re now ready for Stage 2.
Stage 2 – Expose the potatoes to light (at least 10 to 12 hours a day) and drop the temperature to 50º F for the remainder of the 4 week period.
At Wood Prairie farm they’ve built wooden crates to hold the potatoes. They’re stackable and easy to load on their truck when ready to plant. During the green sprouting process they’re housed in a building with lights and temperature control.
A couple of examples were given about how others do it.
- It was suggested that home gardeners could use egg cartons to put the potatoes in for easy transport.
- In Holland where the springs are more mild than in Maine, they put the potatoes on the asphalt in the front yard and put a rain bonnet over them. They’re left outside 24 hours a day. (Can’t do that in Maine because the temperatures that time of year still get to low at night.)
- One Maine farmer put all his potatoes on the back of his pick-up truck in the garage. He put the truck outside during the day and back in the garage at night.
Proper Light for Stage2/ How You Can Tell If It’s Strong Enough
Light can be daylight, fluorescent, or incandescent as long as it’s strong enough.
If the sprouts start to elongate, your light needs to be stronger. Sprout growth should be compact – about 3/4 inch.
In all most every case it’s inadequate lighting that causes sprouts to elongate. (They’re trying to reach more light.)
If sprouts continue to elongate after the lightening is increased, try lowering the temperature from 50º F to 45º F or 40º F.
Managing Respiration in Stage 2 of Green Sprouting
In this final stage of the process you are trying to manage respiration in order that the potatoes will maintain the greatest amount of energy until they can be planted. The more energy that’s maintained, the more yield you can get.
High temperatures will cause high respiration. Tubers will start to shrivel. This shows an energy loss. And energy loss is directly connect to yield.
Temperatures in Both Stages are Important to Success
Gerritsen said that in both steps of the green sprouting process, people tend to get the temperatures wrong. So make note of the temperatures this noted potato grower has indicated and try to stay as close to those as possible.
- Stage 1 – 65ºF to 75ºF
- Stage 2 – 50º F
A Most Valuable Piece of Information – Especially if for some reason you don’t have time for the entire 4 week process.
There is benefit simply from warming up the seed!
About 25 years ago there was an informal experiment that took place. In Maine the State Seed Farm planted 1/2 the seed of one variety of potatoes on a Friday. Since they close on the weekends, the manager put the other half of the cut seed (potatoes) back in the garage and turned the heat up to 75ºF until they could be planted on Monday.
Records were kept and when the potatoes were harvested, the seed that was warmed over the weekend had a 15% higher yield.
Why not do your own test? Just make sure the variety and conditions are the same so your results will be accurate.
I was excited to learn from Jim Gerritsen of Wood Prairie Farm and could hardly wait to share this new understanding about green sprouting with you.
If you’ve had trouble growing potatoes, and/or don’t think you’re getting the yield you should – or if you have a limited amount of space in which to plant – why not give green sprouting a try. Let me know how you do.
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