How to Winter Sow Tomato Seeds

Last Updated on June 26, 2022
   I have been growing tomatoes for over 40 years now, and most of my tomatoes have been grown in Gardens in a back yard.   The past 10 years I have been growing tomatoes in containers.  I have been growing my tomatoes from seed, using a indoor lighting system, every year.
   The past few years, I have been hearing so much about Winter Sowing tomato seeds, that I decided to give it a try.  Winter sowing, in a simple statement is, ” a method of outdoor winter seed germination that requires just two things.  A small, or miniature greenhouse, ( I use 1 gal distilled water jugs)  and some potting mix. “( I use Miracle grow potting mix )   You can use whatever potting mix you desire, but just make sure you use a soil mix that has a light, fluffy consistency, that drains well.
   I thought this Winter Sowing was a great idea, so I decided that I would experiment and give it a try.  I have used 1 gal milk jugs to cover my tomato plants in my garden before, but only for a short period of time, if frost was forecasted,    So, I decided to use 1 gal ( distilled water jug ) as my miniature greenhouse.  These are clear plastic jugs and will allow the sun to shine through.   I get them from Walmart, as they only cost 85 cents a gallon.   I use the distilled water in a lot of my appliances (  Iron, Humidifier, etc.. )  No matter what type of Mini greenhouse  you use, you must make sure to wash them out throughly with Hot soapy water, and mix in some Clorox to kill any germs in the container.  Rinse them well and you are ready to use your greenhouse.    I always peal off the labels that are on the jugs to help the sun shine through.  A little tip to help do this is to run real hot water over the labels ( a couple of minutes ),  to melt the glue under the label, and the label seems to peal off really well then.
   The last two years I have grown some tomato seedlings this way and to my amazement, it works really well.   The plants seem to be a lot more sturdy, strong, and they are already hardened off, so you wont have to do that chore.   I have only used 2 jugs each year, because I still used my indoor lighting system for most of my seedlings.  (  I am so scared of change )  I will have to say one thing about winter sowing though, it is the easiest, most cost effective way to grow tomato seeds into beautiful tomato plants I have ever used.    It sure is a great way to grow tomatoes without spending a bunch of money for a indoor lighting system, and you dont have to harden off the seedlings as they are already hardened off.  Many of my friends loose their tomato seedlings trying to harden their tomato plants off.
   OK, now we need to establish a method to get your mini greenhouse ready to accept your seeds.
   First, drill 3 holes in the top of the jug cap.  ( I use a 1/4 drill bit )  For a lot of you that dont have power tools, you can just take a medium size phillips screwdriver, and heat the point over a flame to get it really hot, and then melt the holes in the plastic with the hot screwdriver.  Also, put three or four holes in the top area of the jug to help in the ventilation of your seedlings and to allow mosture into the jug from rain & snow.  etc…  You must have ventilation for your seedlings.  This is to prevent excess heat from building up inside your greenhouse and baking the seeds to death.  After your seedlings have established themselves ( first set of true leaves ), take the cap off and leave it off.
   Now turn the jug upside down and drill or melt about 5 or 6 holes in the bottom of the jug for drainage.  None of these holes needs to be perfect in shape or size. Now that we have the holes put in the top and bottom of the jug, we need to cut the jug in half to be able to fill the jug with soil mix and have a way to get into the jug to water and check on the seedlings from time to time.    To do this, measure up from the bottom of the jug 4 inches, and make a mark.  I use a felt magic marker.   Do this in several places around each side of the jug.  A cloth measuring tape works really well.   The measurement does not have to be perfect.  We are going to connect the marks and draw a ling all the way around the jug.  This line will help cut the jug in half with a scissors, and allow a small piece left to use as a hinge to hold the two pieces together.
   OK, now drill or melt a couples of holes next to each other together on the line.  Big enough holes to get your scissors tip into the jug to cut on the line.  I have a small craft scissors that works really well, but you can use just about any scissors, as the plastic is thin and easy to cut.  Cut all the way around the jug on the line and STOP cutting before you get to one of the corners.
You need to leave a flap of corner plastic available to act as your hinge to open and shut the jug.
   Now our mini greenhouse is ready to fill with potting mix.  Take a coffee filter and place in the bottom half of the jug and put your potting mix over the coffee filter.  This prevents the roots from growing out of the mini greenhouse.  Fill the bottom half of the jug with potting mix within about one inch from the top.  Water the soil mix really well and let drain.
   Now make a large “X” on top of the soil mix ( from corner to corner ) and make the depth of each leg about 1/4 inches deep.
I want you to put 4 tomato seeds into the 1/4 depth soil mix   Measure up about one inch from the center of the “X” on each leg and plant one seed.  Cover the seeds over with soil mix and pat down the soil mix a bit over the seeds.  You want the seeds spaced close to the center of the bottom of the jug, as we will be thinning out two of the seedlings when they get big.
   Now we have out seeds planted in our mini greenhouse, we need to close up the two sides together.  Take some duct tape and wrap it all the way around the crack of the jug where the top and bottom are joined together.  It dont have to be neat, but make sure you have all the crack covered so that the top and bottom are joined together well.  You will need to have it so that you can take the tape on and off to check seeds and water them from time to time before you transplant them into your garden or container.
Now take time to mark your container as to what it contains.   It is terrible when springtime comes and you have a bunch of jugs filled with seedlings and you dont remember what is in each jug.  A felt magic marker works great to write on the outside of the jug as to what tomato plants are inside.
   OK, time to put the jugs outside in a sunny spot.  In my zone 4, I put my mini greenhouses out into the full sun on April 1 st.  I am sure you southern folks can plant much earlier than this.  I set mine on my front stoop ( which is on my south side of the house )  I get a good 6 to 8 hours of full sun during the day and of course a full night of darkness.   Now it’s time to let Mother Nature do it’s thing.  As the temps freeze and thaw, your seeds will to the same thing.  This will loosen the seed coating and allow the seed to sprout.   In about 3 to 4 weeks, my seeds start to sprout.  When the seedlings get to about 3 inches high, I take off the cap on the jug to allow more ventilation, and open up the jug and check the moisture content.    If it is dry, you need to water them.  Do it gently though, so that you do not disturb the tiny roots or wash out the plants.  Do not allow the seedlings to go dry as this will kill the seedlings.  Keep them moist, but not wet.
   Alright, there is one thing I need to remind people.  TLC ( Tender Loving Care ) is required when growing any tomato seeds.  You must keep an eye on them.  Water, and fertilize them when needed and make sure they are not melting from too hot a sun.   Fertilizer should be diluted way down ( 1 teaspoon per gallon of water ) until seedling gets their second set of true leaves, then make the fertilizer a little stronger until you transplant into garden or containers.
   Remember, Tender seedlings can burn very quickly in too hot a sun.  It’s best, after the seedlings have sprouted, to put them in a spot where they get 6 – 8  hours of full sun and part sun the rest of the day.
   Although winter sowing is a great way to grow tomatoes, there is one problem about early outdoor sowing.  Once your seeds have sprouted, a hard frost will kill your seedlings real easily.  Keep an eye on the weather forecast, and if a hard frost or freeze is in the forecast, cover your mini greenhouse with a blanket for the night, and take the blanket off when the weather warms the next morning. .   If you are a worry wart like me, I will bring my mini greenhouse inside for the night.  That way, if the wind comes up, it wont blow away the blanket and ruin my greenhouse, or kill my seedlings.  It’s definitely your call.
   Ok, now we are going to transplant our seedlings after the last frost date in the Spring.   My last frost date is June 1st.   My seedlings in my mini greenhouse are usually about 6 inches high. We are going to take our scissors and thin the seedlings to just two in each jug.  Take your scissors and cut off two of the seedlings at the base of the stem by the dirt.  All of my seedlings i have planted have sprouted, so I always cut off two of them.  I pick the smallest and thinest and cut them off.   If only three seeds sprout, then just cut off one seedling.  We are going to water the soil mix really well in the jug, and take the whole plant and dirt out of the jug.    Dig a hole as big as the bottom of the half jug.  Pour one cup of a mixture of water & full fertilizer mixture into the the bottom of the hole.  Put the whole plant & dirt from the mini greenhouse into the hole.  Cover all cracks and fill with extra dirt or potting soil around the plants.  Dig a hole for each mini greenhouse you have made.    I know that a lot of you would like to take all the seedlings out of the greenhouse and transplant into your garden.   That will work I am sure, but I dont like to disturb the roots any more than I have to, and this system works so well that you will have great big plants and lots of tomatoes early & late.
Good luck on your Winter seed sowing

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