hardening off seedlings

I hate starting seedlings indoors, but alas, this winter has held on so long that I was desperate to get my tomatoes and peppers started.  So I did, inside.  Now the days are warm enough for them to be out, I'm putting them outside during the day.  But I think they are too leggy and the wind light breeze has knocked some over.  

What do you guys do to harden off seedlings to prepare them for the big wide world that is the garden?  

Up pot your tomatoes to a bigger pot. Bury them deeper, strip off the bottom couple of leaves if needed. They will produce roots all along the buried stem and it will make for a better plant.

I start mine indoors early usually and plan on going from starter flat to recycled cup (I thank the church ladies with bake sale donations in return for them saving their plastic and foam cups after coffee time after service) to trade quart to probably trade gallon before they go out. Then I harden off for a few weeks and I plant them by burying them deeper again, stripping off the bottom few leaves. (12-16 weeks for me to go from starter to out) Some of my biggest beefsteak types (brandywine, big zac, mexico, etc) will probably be in 2-3 trade gallon by the time they go out. Also when dealing with your starts in the house, put a small fan on them once they're a few inches high, GENTLE breeze to ruffle them. It's like an aerobics workout (watch out for drying out) and will make a stockier sturdier plant. I sometimes use a mild preparation of compost tea (maybe half strength) at 10-12 weeks or at the last uppot, plant is not dry and give them a half ration of the tea versus what they normally get for water.

Roots roots roots is the name of the game, and you can un-leg a tomato plant start by up-potting it into a deeper pot and burying it deeper. Tomatoes don't mind a mild root disturb unlike a lot of other plants... if you do an up-pot it should be two weeks before you put the plant in the ground or such for the season. Any sooner, skip and just go directly to planting in ground.

I put them out for the day for about a week, under a leafed tree or 30% shade cloth equivalent, in a wind protected area of the yard. Second week they get some of the wind and sun protection removed and stay out day and night (I pay attention to how cold it's getting, I try to keep them outside if it's upper 40's F, and keep them wind protected at night. You can sort of bunch them together to help prevent the wind from blowing them over, and just plant them deeply when you can put them in the ground. Good Luck.

I used to have a dickens on a time hardening off tomatoes. That was before I discovered the benefits of plastic... An 8 mil sheet of plastic as a canopy over the plants (so that they are open to airflow and don't overheat), will filter out enough UV light that the plants don't get sunburned. About 5 days of that, and they are ready for the garden, or for direct sunlight. I don't care if they get hardened off to wind... I generally don't have much wind at my place unless it's a gale. All bets are off if we have a storm like that!

My greenhouse has plastic glazing panels, so I can take plants directly from inside to the greenhouse, and then to outside a week later without worrying about sunburn. If weather is warm, I open the greenhouse in order to lower humidity, and allow wind in.  A close collaborator runs her hands over the plants, caressing them a few times a day, in order to encourage stockiness.

I've been known to roll up a tomato vine like a spiral when potting it up!

Great advice.

I've never had this challenge before because my tomatoes never got this big before the weather was warm enough for them to harden off.  Today was the first day they could be outside and I think they hate me.  Sunburn and windblown.  So sad.  I'm so ashamed.

The official last frost day is tomorrow and the soil is just about warm enough to put them in the ground.  I bury them deep so that they only have two leaves sticking out of the ground.  They seem to love this.  I might put them in early and cover them with a row cover and hoops.  I'm not good with plants in pots. I want them in the ground ASAP.

You GO! Tomatoes are forgiving and for cherries I end up with at least 8" and more like 12" of root from base of seedling plant to top of soil when I plant out, for big beefsteaks All I Can Get, and Romas and Sauces and smaller (4-12 oz) anything over 12" is a bonus.

The next phase is to make sure as your vines grow, to give them adequate support and to pick out the bottom 12-18" (30-40cm) leaves and suckers as the plant grows. By the time a beefsteak is 3-4 feet tall (a meter approximately or a little more) I have that plant cleaned out at the bottom better than a foot to allow airflow, help keep insects from harboring, and overall set that plant up for 'greatness or growing'.

I grew competition tomatoes, hand pollenated for keeping the genetics known (some have 8 or more verified generations) and up to about 3 to 4 feet, the rearing of the plant is the same whether you want to 'grow for greatness'  or 'grow for production'. It's at that point, when you have the plant well rooted, staked, trellised, or caged (depending on variety) and the whole thing trained, cleaned out at the bottom, and ready to go, what fate it will meet. Whether it is to fill your table and pantry or bend the scale, that much is the same.  

I am at altitude, like Joseph Lofthouse, though he is a few zones warmer and a few thousand feet higher elevation... and UV is an issue. Almost any plant during the 'hardening off' appreciates a layer of 4 mil or heavier plastic, or shade cloth at 30% or equivalent tree shade for the transition. As I said, I plan on an indoor start, three pottings, and putting out huge plants according to when the frost date is. In my 6b, I have gotten RIPE fruit before beginning of July but that took serious work which you're not ready or able to do. No problem.

If in doubt, up pot your tomato seedling to remove any 'legging' issues, use windblocking of the grow area, and keep your hope up!

R, have you thought about putting the plants out and using row covers or maybe even using a cold frame for hardening them off?  

We have wind, lots of it and it comes with velocities in the 15 to 50 mph range. For newly planted items we row cover for a few days/ weeks, depending on how fast they establish.

Like kola Joseph we use plastic for our row covers since we can get several covers from a single roll.

Redhawk

I start my seedlings in March and use grow lights.  If the plants get too crowded (usually tomatoes and cucumbers) I put them in 3-inch pots or peat pots.  To harden them, I start gradually with 1-2 hours of later afternoon sun for a few days eventually building to all day in the sun on my back deck. I have seen a bit of sunburn.  Whenever I end up having to buy seedlings, this is the question I always ask "Have they been hardened?"

Please don’t ever compare your own organic seedlings with the ones you see at the local feed & seed. Their’s are propped up by a steady stream of chemicals from the start. I start my tomatoes in a flat tray and just plant a handful of them together. When they are about 3” tall, I separate and pot them up, discarding any that aren’t strong and have a good root system, burying them down to just below the first true leaves after stripping off any leaves below them. I pot them into 4” pots and they normally stay there until they go into the garden or need repotted because winter won’t seem to leave.

I harden off by sitting all the flats out into the sun starting with an hour a day and being ready to plant by increasing the amount of time in the sun by an hour each day. After 7 days of that they are ready to plant or move to the greenhouse for protection until they can go out. I don’t cover my tomatoes or attempt to grow them in the greenhouse because it’s way too hot for them to stay in. I do want a high tunnel in the future but that’s a ways out. Too many plans and not enough hours in a day.

Lexie Smith wrote:.....
I harden off by sitting all the flats out into the sun starting with an hour a day and being ready to plant by increasing the amount of time in the sun by an hour each day. After 7 days of that they are ready to plant or move to the greenhouse for protection until they can go out.

So we've been starting tomato and pepper seedlings each year under lights and then hardening them off for about 3-4 weeks outside as a routine for about 25 years now.  I think the gods must have been smiling each year they gave me a 'pass' on my ignorance because we generally were successful with just going straight from artificial lighting to "full" sun each spring before the final planting around June 1st and only had a few times where the plants looked sick after the move outdoors.  This year I suspect the patience of the deities wore thin and they finally toasted our seedlings quite thoroughly after the move into the sun.  Now I've learned here and from other sources of this 'stepwise' introduction of the seedlings to natural sunlight as Lexie and others describe....with two bright sunny days in row hurling photons down on the poor plants.  Fortunately, while the cotyledons of the plants were fried, the center growing point survived (just!) and with some TLC, they are now recovering pretty well.  Just can't believe we did not get schooled by Mother Nature on this earlier....

Good description:  https://joegardener.com/podcast/setting-plants-success-spring/

One system that has worked well for me if I am putting the plants out in the morning and bringing them in in the evening, is to have them in a wagon or wheelbarrow.   Makes the carrying easier.

We have erratic weather in the spring, with warm sunny days, then another snow storm, or a warm cycle then a cold cycle.

I want to get the plants out in the sun early in the season, so you can see why I try to make the carrying easier.

Another system that has worked well for me:

I have a compost bin assembled out of 4 pallets.  In the fall I fill it with leaves, and then nasty stinky straw used as deep bedding.

I have any air channels blocked, and the bin filled up.  I let it sit all winter.  I aim for the height of the compost to be low enough to have room for “gallon “ pots plus height of tomato or pepper plant.

When it’s time to get the plants outside for full sunlight, I put the plants on top of the compost.  I use rigid polycarbonate (or what ever) to put across the top of the bin.  I drape a cloth tarp or blanket over the top before I put the plastic waterproof layer on, the a brick or two, depending on how much wind i am expecting.

I don’t like planting leggy plants, though burying the extra stem works well.  With spring coming so late, I like to get as big a root system as possible.  As noted above, after up potting, it’s best to wait for the roots to get enough growth that they will hold the soil together.  When I sell my extras, people have been quite happy to pay a higher price for the hardened off plant with a “big” root ball.  (Pre pandemic I sold for $5 per plant.

Having lived in 9a for the last decade and a half, I never really had to harden off plants. If the first frost wasn't also the last one, they came within a week of each other.....So, I just direct sowed my seeds in their permanent locations and thinned them as needed.
We will be moving to a completely different climate this fall. The area was 5b until recently when it was changed to 6a. The shortened growing season has me thinking about how my gardening process will need to change and I will adapt to the new conditions. I do plan on building some sort of greenhouse structure, not only for the growing season extension, but we will be living with tons of wildlife and if I don't protect my food crop, I'll just end up with some very fat deer in the woods.

Starting my plants indoors and going through the hardening process is an option we are considering. The new home turf is at 7300 feet of elevation and just had its last snow (hopefully) about a week ago. I'm planning on starting plants between March 15 and April 1 next year. Is that enough time? Seems like a month to 6 weeks should be OK, but I have zero experience with this to gauge from. If they go from indoor starts into the greenhouse does that change anything? I guess I need to build it and see what the climate inside is like to know how to best use it.

That's tricky to answer because I don't do it much. I've usually direct sown, results be damned.

That said, the weather has to be agreeable when you first start moving them out into the big, wide world. Put them out for a few hours a day when there isn't a deluge, a hurricane, or a scorcher. A gentle breeze is best for them, Increase the time they're out each day until they're ready to plant.

j

Joshua States wrote:.... I'm planning on starting plants between March 15 and April 1 next year. Is that enough time? Seems like a month to 6 weeks should be OK, but I have zero experience with this to gauge from. If they go from indoor starts into the greenhouse does that change anything? I guess I need to build it and see what the climate inside is like to know how to best use it.

We've tried greenhouse situations in earlier days as a bridge between starting plants indoors and getting them outside into the garden.  We had too many experiences where the greenhouse could not be opened and closed in a timely fashion and too many things cooked because the greenhouse got too hot.  Because the short summers near the Canadian border nevertheless come with long days, we are resigned to moving plants into the garden no earlier than June 1st.   More recently, we start seeds indoors for tomatoes, cucumbers, and peppers during the 3rd or 4th week at the end of April.  If we *properly* begin hardening them off in early May, their time outdoors leading up to June normally gives them a good head start on growing.  Outside of a bit of root shock from planting, they take off quickly once in the ground.  When we have started from seed in March, we've had more trouble keeping them 'happy' until transplanting arrives....more disease, more 'leggy-ness', and less happy after transplanting.