Steps and tips to caring for both flower and vegetable seedlings at week 6 (or week five, if needed) after starting them from seed indoors, including how to fertilize, pot up if needed, and harden them off for planting.
You can find more seed starting information in our Seed Starting Guide.
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After planning, starting seeds, doing the week 1 care for them, this part of the Vegetable 101 Series takes the next steps for your baby seedlings after five to six weeks - how to care for them and how to get them ready for planting in the garden (the dreaded "hardening them off").
This can be a crucial time - and to be honest, it's when I've most felt like throwing in the towel and just buying the seedlings at times.
- Sometimes they don't look very healthy.
- Sometimes I've lost a few seedlings.
- Sometimes during hardening off, I've forgotten them outside all night.
- Most of the time my excitement over starting the seeds is waning as the outdoor tasks take more time.
But here's where I encourage you with what I've learned:
With just a little care, your seedlings, no matter what they look like, can grow and will produce food (or flowers) for you and your family.
And it's a wonderful feeling to have grown that vegetable from all the way from seed to sitting on your table, right?
Between five and six weeks, what does caring for seedlings look like?
Basically one of three things:
- Repot, if needed, and stake any warm-weather seedlings like tomatoes and peppers that will stay indoors for awhile longer.
- Fertilize the warm-weather seedlings.
- Harden off cool-weather seedlings (lettuce, onions, broccoli, etc.).
Since the care for seedlings at this point is different for plants that can take cooler weather and those that need warmer nighttime lows, I'm separating the care into cool and warm weather crops.
Caring for Flower & Vegetable Seedlings at 5-6 Weeks: Warm Weather Crops
Plants that prefer warm weather (night time lows consistently 50 degrees and above) include tomatoes, peppers, zucchini, zinnias, cosmos and sunflowers.
Your pepper and tomato starts will be between 2-inches (some of the slow-growing peppers) and a foot or more (the indeterminate tomatoes).
Depending on the size of pots you started your seeds in, you will probably need to repot some (or all) of the seedlings to larger 4-inch pots.
This is especially true if you used the 6-cell pots in the seedling trays.
They're great for saving space and starting a lot of plants, but the longer growing warm-weather seedlings will need more room for their roots to grow.
How to Repot
Simply fill 4-inch pots with potting soil and gently transplant your tomatoes into the center as low as possible so you can mound the soil up around the stem (it will grow more roots and be healthier).
Then, place a thin stick (I use dollar store bamboo skewers) next to the stem and hold it to the stem with a loose twisty. This keeps your plants from flopping and once I started doing this really helped the plants during transplanting time.
Water well and place back under the lights. If your new potting soil has fertilizer added, plain water is fine. If not, add fertilizer to the water (seed #4 below).
In order to provide light as close as possible to the plants, your shop/grow light may look like mine above: one side of the shop light is raised to fit the tallest seedlings, while the other side is left low to be closer to the smaller seedlings.
It's not that pretty, but need outweighs looks in this case! The peppers are to the left, tomatoes on the right.
The seedlings will need another application of diluted fish emulsion fertilizer if the new soil you've used doesn't have any. You can use an old gallon milk jug with the recommended amount of fertilizer added first and then filled with water.
Water from the bottom, filling the trays about half full.
Oh, and be sure to get a no-odor fish fertilizer if your seeds are inside, otherwise it's pretty pungent.
Other than that, it's just continuing with consistent watering and light for your warm weather plants until they are hardened off (see more on this below) and planted out according to the timeline in your area.
For me, it's best to plant tomatoes around the first week of May here in the central Willamette Valley.
For peppers, I usually wait until the last week of May or first week of June - and then using a pepper house - since they're really susceptible to any nighttime temps under 50 degrees which can stunt their growth.
Caring for Flower & Vegetable Seedlings at 5-6 Weeks: Cool-Weather Crops
Plants that can take cooler temperatures (though not freezing, usually, unless covered) include onions, cabbage, broccoli, kale, cauliflower, spinach, lettuce, alyssum, and marigolds.
At the 5 to 6-week mark, your cool-weather crops - the tray shown above has onions, broccoli/cauliflower/cabbage and lettuces (right to left)- should look similar to the picture above.
Like you see, they should be fairly green and healthy-looking, not too overgrown or lanky, and ready to be hardened off for a week or so before planting outside.
However, just a year or two later, I had seedlings that looked like this:
I'm not exactly sure why these seedlings grew so leggy - maybe the light wasn't as close or I applied too much diluted fish fertilizer - but for whatever reason, they don't look as healthy, do they?
But guess what?
I planted them anyway, used a row cover (best investment ever to early growth and keeping the bugs away!) and they grew and produced food for us. I think maybe a few of the cauliflower didn't grow, but I find them to be touchy a lot of the time anyway.
The lesson? Plant anyway - as in all of life, the garden doesn't have to be perfect!
Your cool-weather crops won't need to be repotted, since they are going to be planted out soon, but they should remain consistently watered.
If you haven't fertilized with a liquid fish emulsion yet, you may notice a few yellowing leaves since the roots have pretty much used up what was in the little planting pockets.
Go ahead and fertilize the plants so they will have food for the hardening off stage.
4. Hardening Off
The biggest task at six weeks is to "harden off" your baby plants:
How to Harden Off Seedlings
Definition: Hardening off plants is the process of preparing plants started indoors for the change in environmental conditions they will encounter when permanently moved outdoors.
So, those tender little seedlings you've been nurturing need to be prepared for outside because they have been in our nice warm houses and they would go into major shock if we just stuck them right in the ground to be battered by wind, rain, and cold.
Ideal steps To Harden Off Seedlings
- Bring the tray of seedlings outside each day for about a week.
- Start them in a sheltered area, out of direct sunlight.
- Leave them out longer each time - but not overnight - starting with a couple hours and adding a 3-4 hours each day. Also gradually increase the amount of sunlight they have - but never direct for hours or they will cook in their little cells.
- Keep them consistently watered - it's crucial. And they will use water more outside, so check them daily.
- By the end of the week they are ready to be outside all the time.
OK, that's ideally - and wonderful if it all works out like that.
But sometimes this is what happens at my house:
- Seedlings left out for a couple of hours on day 1 in a shady area.
- Forget to take them out on day 2 until the afternoon around 3:00. Then forget and leave them out overnight.
- Go running out to check on them (they're under cover on a table on the porch, so aren't being pummeled by the rain), they look fine so I leave them, thinking I'd be going backwards to bring them back in now...
So instead of a week, they get maybe three days.
This still works, believe it or not, and I was able to use them mainly because they were are cool-weather loving plants.
However, if I had done this with the peppers, I'd be buying more peppers at the nursery!
All this to say- life happens, but garden anyway!
Do you have any tips to hardening off your seedlings?
Note: This article has been updated - it was originally published in 2009, updated in 2016 and again in 2022.
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