Pricking out, potting up, hardening off
“Anything grown in a greenhouse must be properly hardened off in a sheltered spot outside for at least a week (preferably two) before being planted out. You will gain nothing by attempting to take shortcuts with this.”
— Monty Don, “The Complete Gardener,” 2009
You probably don’t enjoy moving from your warm house to a cold car in the morning; well, seedlings don’t like rapid temperature changes, either. They experience transplant shock and will just sit in the soil for a while to acclimatize before starting to establish their root system and grow.
If gardeners understand that plants are a lot like us and need time to adapt to change, then perhaps we won’t mind taking the extra time and effort needed to introduce them to the outside world a little bit at a time. That’s exactly what I’m finding I need these days as I begin to venture out a little more.
Hardening off young plants is particularly important when the spring weather fluctuates as much as ours does in the Rogue Valley. Today, for example, it’s 60 degrees and sunny in my backyard, whereas yesterday was overcast and cool, reaching only 53 degrees. Seedlings that are exposed to different kinds of weather before they’re planted out will be better adapted to our garden conditions and, therefore, will have a jump-start on growing into strong, healthy plants.
This doesn’t mean hardening off is without risks. Not only was yesterday chilly, but a sudden late afternoon hail shower pelted the seedlings I had placed outside on my bench. Some of the seedlings succumbed to this cruel onslaught. I cussed a lot and then vowed to replace the bench with a protected cold frame as soon as I get the chance.
In my experience, hardening off is literally “do or die” time for young plants. If they get through two weeks of part-time exposure to the outside elements, then they usually do well once they’re set out in the garden. Sturdy plants are less susceptible to disease and insect predators.
Risks and all, it’s a good idea to begin hardening off seedlings that are started indoors once they grow one or two sets of “true” leaves. The first set of leaves are the cotyledons or seed leaves; the true leaves start with the second set and these are the leaves that can perform photosynthesis.
I put my seedlings outside where they receive partial afternoon sun; other gardeners place their seedlings out of direct sunlight. If you can, start by bringing the seedlings outside for a few hours and work up to all day. I’ve been putting my seedlings out around lunchtime and bringing them back in around dusk, but I’ll try to start placing them out earlier and earlier as morning temperatures warm up.
I’m trying out “soil” blocks and coir plugs for starting seeds indoors this year. I’m finding that timing is particularly important with the plugs because coconut coir does not provide any nutrition. If the seedlings grow one or two sets of true leaves too early to plant out, I have to plant the plugs in larger pots with a balanced ratio of compost/coir/perlite to feed the seedlings and support healthy root growth.
I’ve been placing the coir plug directly into a 4-inch pot with a bit of growing medium on the bottom, filling around the plug with the medium, giving the pot a gentle shake to settle the medium, and watering thoroughly. The potted up seedlings are then placed outside for the hardening off process.
Although the soil blocks take longer to make, and I’m finding they sometimes break apart in the tray, their advantage is that seedlings can stay in the blocks longer with more room to grow roots and more nutrition provided by the compost in the growing medium.
Whether sown in soil blocks, coir plugs, cell packs or trays, pricking out seedlings is another important part of growing healthy plants. I said that hardening off is “do or die” time for my seedlings, but that’s after they make it past the pricking-out cut. I try to sow seeds as thinly as possible; however, multiple seedlings often emerge and I have to make a tough decision about which seedling to save.
I look for the seedling with the thickest stem, healthiest seed leaves and most vibrant color. Sometimes I choose the seedling that is in the best position in the plug or block, and sometimes I choose the youngest seedling to emerge because the timing for planting it out fits better.
Once the choice is made, I use a small pair of scissors to cut off the seedlings I don’t want as close to the surface of the growing medium as possible. Pulling the seedlings out risks damaging the root system of the plants I want.
Pricking out, potting up and hardening off seedlings are important follow-up tasks to sowing seeds indoors. This is pleasant work that establishes a rhythm to my early spring gardening. In fact, one of the things I’ve enjoyed the most about reading Monty Don’s book is the way he shares his experiences of each season in his gardens at Longmeadow. I love the way he describes this time of year.
He writes: “Spring shows itself first in tiny details, like the curlews arriving in the water meadows, the first primroses and violets in the coppice, the catkins on the hazel, or the blackthorn blossom in the hedgerows.”
This landscape sounds very British, but Don’s description reminds me to savor the tiny details of spring in my garden, like the cloud of pink appearing on the plum tree, the cheerful yellow of the forsythia branches, and the clusters of purple grape hyacinth.
I’ve only scratched the surface of what Don offers in “The Complete Gardener,” so I’ll be referring back to the book, in my gardening and in my columns, throughout the growing season.
Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at Rnowak39@gmail.com. For more about gardening, check out her podcasts at https://mailtribune.com/podcasts/the-literary-gardener and her website at www.literarygardener.com.
Continue sowing annual vegetable and flower seeds, pricking out, potting up, hardening off.
Plant out peas, lettuce, kale, cabbage, carrots, beets and other cool-weather crops after hardening off (have row cover handy for cold nights).
Add fresh compost and leaf mold while planting beds and borders.
Sow grass seed to cover bare spots in grass pathways; keep moist.