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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Wow!.so happy to see the info on potatoes. One of my challenges for next years garden is to grow potatoes. In recent years I have always planted a few in a container just for the joy of watching them grow. The yield was never enough to provide a meal, but served as a “treat”. This year I will leave room for a larger quantity of potatoes in one of the raised beds. I have always purchased organic seed potatoes at our local nursery so as to get a variety for our area.
Have to share this fun garden story with you, however you may have heard it already as I have been a reader since I started to garden here in Northern Nevada. During the first years we built the beds, I tried sheet composting and scattered potato peels in the garden along with other vegetable waste. Weeeeeellllllll, can you imagine my surprise when all the dark green plants popped up throughout the garden. Not the first time I’ve failed to follow the instruction, (they recommended not using potato peels) but a lesson well learned. It took a couple years to get rid of them. If I had the space I would leave the plant and we would have gotten another “treat”.
I control apical dominance on my apple trees, but never would have thought about it for potatoes. This explains why I only see one main sprout from potatoes and also why I only get a few from each seed. Wow, thanks so much! P.S. Starting my wintersown today…Julie
Well, potatoes were on my learn to grow list for this year, too. Thanks Theresa. I guess I always feel disappointment because the cost to order seed potatoes is high relative to what a packet of seeds costs, and so I expect so much more from them. I’ve been disappointed so far in my potato growing, but perhaps this might change things for the better. I will definitely try this. Thanks for sharing what you are learning, Theresa as always.
Excellent article. Thanks. I have gotten potatoes from this company thru SESE and they are always beautiful and healthy sets. However this way I do not have control over when the sets are sent to me and it seems as though I always wish I could have planted a little earlier.
Please speak to the soil temperature needed for planting. Or is there a difference in sprouting or yield with different soil temps? I live in the same zone as you in VA and always aim to plant as close as I can to St Patrick’s Day if I have potatoes then.
Glad you’re planning for more potatoes this year Alice. They are so delicious! Nothing beats fresh grown!
I found your comment enlightening Julie, because I never related apical dominance to apple trees. (Have not grown them.)
I’ve got to get started with wintersown as well.
Sandra, I remember your saying that you didn’t have good luck with potatoes. Green sprouting could very well be your answer.
Wood Prairie usually ships their potatoes relatively early Bonny. As long as the weather is not freezing they’ll ship. So you’ll have them in plenty of time.
As far as soil temperature:
For many years I use to plant about mid March (St. Patrick’s Day)
Now I don’t plant that early because my soil is just too cold then and they sit there.
I stagger plantings. I plant early potatoes the first part of April; then mid April I’ll plant midseason or late varieties.
Sometimes I plant late varieties at the end of April or the first of May.
I usually don’t take the soil temperature. I just go by what’s going on in the garden.
And I know early April through the first of May work well for me.
Potatoes can take a wide range of temperatures – from 40 to 80, but I think 50 to 65 would be a perfect range.
Thank you for this post. I have grown potatoes in a 3 foot round pile of compost about 3 feet deep and added soil, more light compost as they grew, but have been disappointed in the small yield.
I am interested in trying this. The warm will be easy as I can use a heat mat. a constant cool temperature will be harder as it gets colder than that at night here in the spring (early spring).
Also, it takes a lot of my valuable compost. Any ideas?
Excuse my ignorance, but why can’t you just cut back the king shoot to encourage the growth of the secondaries?
FrankG, The goal is to suppress apical dominance to promote even sprouting. This suppression is accomplished by sprouting the seed potatoes at a temperature of 70-75oF. Suppression of apical dominance via temperature management will both retard the king sprout AND PROMOTE SPROUTING FROM SECONDARY EYES. Simply breaking off the king sprout mechanically would have minimal beneficial impact on helping those secondaries wake up and get growing.
Jim Gerritsen, Wood Prairie Farm, Bridgewater, Maine
I very much appreciate your sharing.
I’m sure this is not something most people know, and it’s definitely not self-evident.
Theresa, thank you as well. Your knowledge and dedication are appreciated by many.
Last season was the second year I planted potatoes and the first year I learned about “chitting”. I set my seed potatoes in egg cartons (in sunny window) as described in your article. Two things I noticed when compared to previous year (w/o chitting)…yields were approx 2X higher, and much earlier than simply placing seed potato in ground with no green sprouting. I was not aware of controlling temp conditions, but am hopeful for even better results if I can add this to my process. As always, your TMG articles are point on!!
Any study on yield when planting the whole potato vs. cutting into sections with eyes?
Question…due to limited space in my garden beds for potatoes, I also use an upright vertical support called a “tater tower” which is basically a rigid plastic tube approx 4-ft tall with lots of holes for drainage/ventilation. The question is…are there certain types of tubers that would grow better in “sections” of soil? That is, with each ten inch depth of soil, I plant the tubers. After the plant greens have grown one foot tall, I add more tubers along with another ten inches of soil…layering like this until the four foot tube is full and the greens are growing out of the top. At the end of the growing season, I simply dump the plastic tube over and dig out my spuds. I have read that some varieties do better in this application than others, but if this is true…am not aware which type would produce more??? Any ideas?
Don — I’m not sure I understand the details of what you have in mind.
When the temperatures drops at night, you’ll have to bring your potatoes inside. Put them back outside the next day.
If you’re disappointed in the yield in the compost pile, why not try planting some in your garden. See if things don’t improve. Why not do a test – a few in the compost pile and few in the garden.
Tony P –
I wish Jim Gerritsen were available to answer your question.
I feel sure he’d know.
I can tell you a few things that may be helpful:
I’ve planted both ways many times. I get good yield both ways BUT I don’t weigh the yield etc or keep detailed record.
The most significant thing I can tell you is that Jim G cuts his before he plants. That make me think cutting would be the best way.
I’m an “in the ground” planter the majority of the time.
I don’t know anything about varieties that would be better for planting in a “container”.
If I have the opportunity to correspond with Jim Gerritsen, I’ll ask him Tony’s question and yours.
Bonnie: We ship our seed potatoes to retail customers 10 months per year from Sept until July 4 – including throughout the midst of winter. If you place an order directly with us simply tell us when you want them and we will oblige.
Tony P: We aim for seed pieces which weigh 1.5 ounces (10/pound). Studies have shown no yield increase when seed piece size ranges from 1.5 oz to 2.75 oz. Yields start to trend upwards a tad above 2.75 oz but bear in mind you would be using TWICE as much seed/acre or hundred-row-feet so that is a significant trade-off.
Jim S: You might experiment with the Cornell variety “Elba” (it is one we grow and sell). Years ago our wholesale customer Gardeners Supply in VT tested a boatload of different varieties for container gardening and Elba came out on top. I believe the yield-drag on container gardening is often attributable to insufficient watering. People have a hard time perceiving just how much water a potato plant needs especially during tuber bulking. Thirsty plants produce smaller tubers.
Hope this is helpful.
Wood Prairie Farm
Jim G. & Theresa,
REALLY appreciate the info as well as you both sharing your knowledge & expertise with others! I’m gonna give the Elba variety a try and thanks once again!
I’m wondering if I can plant after the first week in the warm darkness and still have a benefit?
Teresa, although I think the idea is to get the potatoes to break dormancy. (When they do you see signs of sprouting.) BUT, if all you can do is keep them warm for a week, go for it. It certainly can’t hurt and probably will bring them that much close to breaking dormancy.