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Garden, Plants

How to grow great sweet peas

March 12, 2019

Sweet peas

According to my seed-starting spreadsheet, which I make every year to tell me when and how I’m supposed to be starting seeds, March 14 was the day to start my sweet peas. But I couldn’t wait any longer so I got all wild and crazy and planted them last weekend. (I’m a seed-starting rebel, I tell you!)

If I could only grow one flower from seed, it would be sweet peas, simply because you cannot find decent sweet pea plants at garden centers. And when you can find them they likely won’t transplant well because sweet peas just don’t appreciate that kind of treatment. To me, sweet peas smell like a garden. It is a scent you can’t find anywhere else and one you’ll never forget. That alone makes the bit of fuss required to grow them worth it to me.

It looks like I first started growing sweet peas in 2015 (based on this blog post) but I can’t believe it hasn’t been longer. I’ve always had moderate to good success with them, but I feel like I’m getting better at it every year. 

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'Prince of Orange' sweet peas

‘Prince of Orange’ was gorgeous last year and made it on my must-grow list.

Here’s how I grow them these days.

I started growing them in root trainers last year and I feel like this was a positive change over the 4-inch pots I used to sow them in. Root trainers are small but long cells that allow plants to develop nice long roots. They open up like a book so it’s easy to remove the plug when it’s time to transplant them. The idea is that you can sneak these fussy plants that don’t like their roots disturbed into the ground without them really noticing. 

sweet pea seeds

This year’s sweet pea selection that I’ll be growing.

Before I plant anything, I make a label for every single root trainer cell. No matter how much I think I remember that one whole row is one kind of sweet pea, I forget, so now every plant gets its own label with the name on one side and the color on the back along with the date I sowed it on. It’s terrible to have to go back to the plant packets and look up what color a sweet pea is when I’m ready to plant. 

Sweet pea plant label

Every plant gets its own label with the name of the variety, color and date sown.

To soak or not to soak: that is the question. Actually that’s only one of the questions when it comes to how to treat sweet pea seeds. Soaking, nicking (or roughing up with sandpaper) or pre-sprouting all have their fans. I did a little trial years ago in which I grew nicked seeds, soaked seeds and plain old seeds and the result as that none of that made a difference. Pretty much everything germinated. 

sweet pea seds

Sweet pea seeds can be tan to dark brown or even gray.

I see a lot of people pre-sprouting their sweet peas in damp paper towel, but I’ve never done this because it just seems like an extra step that I don’t feel like bothering with.

So I plant seeds—two per root trainer cell—straight into pre-moistened seed-starting mix about a half-inch deep. I always cover my seeds with vermiculite to prevent a crust from forming on top of the soil as well.

Sweet peas like a bit of warmth to get going, so I cover the root trainers with plastic—a humidity dome doesn’t fit on it—then put them on the germination heat mat and throw a towel over the whole thing to maximize the warmth.

Root trainers for sweet peas

Root trainers allow the plants to stretch their roots with little disturbance when transplanting.

Once most of them have germinated—and I find that sweet peas are extremely unpredictable in how long they take to germinate so there are always some laggers—I’ll move them under the grow lights and make sure to keep them moist (as you would with any seedlings).

When they grow to have about four leaves I pinch them all back to two leaves to promote branching for nice bushy plants. 

Sweet peas don’t like a lot of heat so they are one of the first things I move out to the temporary greenhouse. I almost never fertilize seedlings, but sweet peas seem to need a little boost right around the time I pinch them back so I feed them with very diluted fish fertilizer. 

They can be planted out quite early. Earlier, in fact, than I typically do and this year I’m going to try to stay on top of that a bit more. They can even handle a light frost and they certainly prefer to be growing in the ground, so move them on as soon as you can.

Sweet pea bouquet

One of many sweet pea bouquets of a recent summer.

Sweet peas are particular. They like rich soil (this is true of many vining plants). They don’t like it to get too hot. And they aren’t fond of highly acidic soils (not a problem in my garden). In general my attitude to these demands is something along the lines of, “Suck it up buttercup. You get what you get.” But if I’m feeling particularly generous I will work some manure or compost into the area where I’ll be planting them about a week or two before.

Of course I stay on top the watering and give them a good amount of sun. It just doesn’t get hot enough here to worry about shielding them from hot afternoon sun, but it can help in hotter areas. They do need something to vine on. Some people use plastic mesh (the kind with 1-inch holes) supported on canes, but I prefer to train them up bamboo teepees. I tie in the stems until they are about 18 inches to 2 feet tall and from there they support themselves.

'Erehwon' sweet pea bouquet

‘Erehwon’ is prominently featured in this quick-pick bouquet.

Beyond that my only sweet pea specific rule is to pick them, pick them, pick them. Sweet peas just keep going if you don’t let them set seed, but if you let even a few flowers to seed the whole plant gets sulky, as though it decides its job is done. So I make it a point to try to cut sweet peas every couple days when they are in flower. This means I have many tiny sweet pea bouquets around the house. And you won’t find me complaining about that. 

seed starting seeds sweet peas
by Erin @ The Impatient Gardener 
21 Comments

About Erin @ The Impatient Gardener

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previous post: You won’t believe the big seed-saving mistake I made
next post: Can we just talk about faux plants?

Comments

  1. lynda says: March 13, 2019 at 6:47 am

    I love sweet peas and bought seeds to plant this year. I remember them growing in the winter in Southern California. Do you give the plants something to climb on? There is nothing like that wonder sweet pea smell!

    Reply
    • Erin @ The Impatient Gardener says: March 13, 2019 at 9:41 pm

      Yes, you either need to give them something small to vine up such as plastic mesh or you need to tie them into something like bamboo canes until they get big enough to support themselves. Thanks for asking because I forgot to address this. I’ve gone back to add it in.

      Reply
  2. Lady Locust says: March 13, 2019 at 3:13 pm

    I to love sweet peas. I am hoping to plant them next to the front steps so they can vine up the railing.

    Reply
    • Erin @ The Impatient Gardener says: March 13, 2019 at 9:40 pm

      That would be the best welcome home.

      Reply
  3. Debbie - MountainMama says: March 13, 2019 at 3:36 pm

    Thank you for this – I’m growing sweet peas this year for the first time in years, and this is such helpful information!!

    Reply
    • Erin @ The Impatient Gardener says: March 13, 2019 at 9:40 pm

      Good luck! There’s nothing like sweet peas!

      Reply
  4. Heather says: March 13, 2019 at 5:08 pm

    I’ve never grown sweet peas, nor have I heard of the deep root trainers. Looks like I’ll be trying both! Thanks for the great post!

    Reply
    • Erin @ The Impatient Gardener says: March 13, 2019 at 9:39 pm

      You can grow them in 4-inch pots too! Good luck!

      Reply
  5. Joyce Bradley says: March 14, 2019 at 1:59 pm

    Is it possible for you to post a photo of them all in bloom. I’d like to see the spacing of the plAnts….besides seeing how pretty!

    Reply
  6. Kelly Fischer says: April 1, 2019 at 10:07 am

    This is my first year starting sweet peas. On the seed packet it says sweet peas need darkness to germinate and recommends covering them with newspaper if starting them inside. What are your thoughts? Have you ever done this?

    Reply
  7. Johnny Pemberton says: April 14, 2019 at 11:56 am

    these are beautiful. have you ever tried to growing shelling peas (pisum sativum) nearby? i just learned that sweet peas are a completely different species.

    Reply
  8. Michaele Lockhart says: May 12, 2019 at 4:35 pm

    Hello, I’m writing from Tucson, AZ. Here in the desert Southwest we have a a different regime with sweet peas. We’re supposed to plant them in September “by the full moon” (I don’t think you have to do it at night, just during that phase of the moon). I plant in the garden. I don’t knick or sprout either. They start sprouting in mid-January. They usually finish blooming by the end of April. The sun is very strong here. Unless the area is very protected, or only with an eastern exposure, that is what works for me.

    Reply
  9. Tori says: March 11, 2020 at 6:56 pm

    Wonderful post! I’m new to growing sweet peas and I keep wondering the reason for planting two seeds per cell/container? Also, do you snip the tops off before you plant them outside? Mine are about 6 inches tall and have 2 to 3 sets of leaves. I think it’s time because they are already growing little tendrils. ?. My planting bed isn’t quite ready due to the ridiculous amount of rain we’ve had all winter.

    Reply
  10. Billie says: April 23, 2020 at 3:28 pm

    Love love love your passion for sweetpeas. My dear departed Auntie was a genius with sweet peas. My question to you; if they are tempramental when transplanting from store bought….why can you grow in pots to be transplanted later.

    Reply
    • Erin @ The Impatient Gardener says: April 23, 2020 at 3:38 pm

      I suspect it’s because they have a short window of when they are happy to be transplanted, and the nature of plants in garden centers are that things might sit for awhile. If you grow them yourself, you can transplant at just the right moment (or at least try to).

      Reply
  11. Lana says: October 28, 2020 at 1:42 pm

    Can you please show a picture of brand new sprouting sweet pea plants?

    I planted some and I don’t know what they look like? Thank you.

    Reply
  12. Jan of Issaquah WA says: January 10, 2021 at 7:38 pm

    How important it is to germinate in darkness? The packet of seeds says it is a must. What? Why?

    Reply
  13. Nora says: March 29, 2021 at 11:32 pm

    When do you place the root starter plants under a grow light? At first germination or do you wait for the stragglers?

    At what point do you take away the heat mat?

    Thanks in advance for the response – I have 2 germinated but they look leggy and it’s my first time and I really dream of sweet peas.

    Reply
  14. Brenda says: May 6, 2021 at 8:23 am

    Would you share the where you got your sweet peas seed?

    Reply
  15. Shirley says: March 28, 2022 at 2:40 pm

    Hi, where can i buy root trainers? I googled it and got zero results. I live in Alberta, Canada. Thanks!
    Shirley.

    Reply

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The Impatient Gardener

Do you love gardening? Me too! I'm Erin and I garden in Southeastern Wisconsin, zone 5. The Impatient Gardener is all about real-life gardening: the good parts, the bad bits and even the funny stuff. It's part information, part inspiration and a little bit commiseration. Thanks for visiting.

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E R I N 🌿 The Impatient Gardener
I had a rather unpleasant realization last night w I had a rather unpleasant realization last night when I remembered that I’d not yet ordered tomato seeds. And I’m not going to rectify that until I dig into my seed stash, because I don’t go through tomato seeds quickly so there are definitely some lurking down there. 

I never used to grow tomatoes from seed because there are great varieties to be had in garden centers (including many heirloom varieties). But it’s almost non-negotiable for me now that I’m a convert to dwarf tomatoes. If you’re not familiar with the #dwarftomatoproject championed by @nctomatoman and others, these are heirloom varieties that are crossed with dwarf varieties to create plant that produces all the flavor and interest of an heirloom in a short (usually less than 4 feet) plant. 

They are particularly great in my tall raised beds. Of course I leave room to try new non-dwarf varieties every year (I loved Sun Dipper from @panamseed last year and I’ll grow it again).

Last year was a good tomato year and the photo shows some of the varieties I harvested in one day. I hope this summer will be equally good for the tomato harvest. 

One of my favorite questions to ask gardeners is: What is your favorite tomato variety to grow? So have at it in the comments because inquiring minds want to know!
And this is why I leave my winter containers assem And this is why I leave my winter containers assembled until at least March. A dusting of snow gives them a whole new look (even if it’s shades of gray). Also, I think I love my Limelight hydrangea even more in winter. Fabulous winter interest!
I’m going to look for opportunities to add more I’m going to look for opportunities to add more ferns to my garden this year. They are such interesting plants and often real problem solvers, bringing texture and color to places that many plants aren’t interested in. Athyrium niponicum (Japanese painted fern) ‘Crested Surf’ grows well for me in part shade (even pushing a bit into part sun) and looks great next to Persicaria ‘Golden Arrow’.
Birds chirping, glorious fresh (i.e. not nibbled o Birds chirping, glorious fresh (i.e. not nibbled on) foliage, and texture galore. I can’t wait to have moments like this again. The star, by the way is Hakonechloa ‘All Gold’ which looks so good with the bold foliage of Ligularia dentata ‘Desdemona’ next to it. 

With the new path, this area will be getting a small revamp. It’s the next spot I’ll be focusing my planning on.
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