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How to Grow Sweet Peas

In my first season of growing sweet peas, I knew I would become a lifelong fan. They are the sort of flowers that bring out the child in me and would make a great project to grow with children. I also like a challenge. Here in Texas, at least in Austin, the growing emphasis is on sustainable landscape, and somehow old-fashioned annuals–here today, gone tomorrow–just don’t fit. But truly, these are worth the short season, just as much as tomatoes are worth their short season.

I have seen sweet peas blooming in Scotland in September, in Cape Cod in August, and in Texas in April. And April is really the month they are at their best here.

While sweet peas are a cooler-season annual, It is possible to grow sweet peas in Texas, and it should be. After all, their native climate is Sicily and southern Italy, whose summers are hot. But because they have been largely developed for cooler climates and there are limited publishings about how to grow them here, I went on a research adventure about the history of sweet peas, their natural climates, their different types and growing needs. I tend to like to learn through books as much as experience, and learning even their history helped me make more informed decisions about which kinds to try here. For more information on the specific varieties I’ve tried, visit my Sweet Pea plant page or read on about Winter-blooming Sweet Peas which are particularly suitable for a long-growing season in Texas.

There are several online instructions about how to grow sweet peas–check them out at Renee’s Garden and Fragrant Garden (has some more detail as well as potential problems). But if you’d like more details especially about how I grew them in Texas read on.

The main thing to consider with sweet peas is that they are cool-season annuals. Which usually means: in cool climates they flower in spring and summer, and in hot climates, flower in winter and spring. Many hardy annuals bloom all through the winter in Texas, while some spend their winter growing roots and begin to bloom in March. Sweet peas can withstand some frosts and should be able to sail through the winter without much protection. There are also special sweet peas that have been bred to bloom in winter, and while they were created to be greenhouse-grown for florists in northern climates, in our climate we can enjoy them outdoors.

They are not “hardy” to heat. (And oh, I wish plant descriptions more often considered the hardiness of hotter side of the world.) In Texas, temperatures can soar into the 90s as early as May, and most cool-season annuals hate these temperatures and will quickly drop their flowers, go to seed, and die away. So your aim is to have sweet peas blooming before late May. (You can have them as early as January, but a majority of them will bloom in March and April.)

The best time to plant sweet peas is in fall and right when the temperatures start getting cooler. In Austin there is usually a window in October when the soil is still warm enough to cause flowers to germinate but will cool down not long after so as not to stress the plants out. I usually sow my wildflowers in this time, and I planted sweet peas at the same time as I planted bluebonnets. (They are both in the pea family, they have the same growth patterns–starting slowly at first, spending the winter growing roots, and then taking off in early February.)

This year I am trying a few September sowings to see if I can get earlier blooms from some sweet peas. In the high heat of September, young plants do germinate but grow quickly and can get leggy and I have to monitor their watering needs a bit more. It is also possible to plant in November or December but they might germinate more slowly. It is possible that newly germinated seedlings can suffer more from frost than more mature ones, but variable Texas winters are always a gamble gardeners are willing to risk (a lot more than our summers!).

Sweet peas like fertile and well-drained soil. I have heavy clay soil which I’ve amended with compost and other draining aids. Old-time advice on sweet peas suggests digging a trench as you would for veggies and putting manure in the bottom. The point is that they like a really rich soil that gives them the opportunity to send long roots down as deep as they can. There is just so little that will survive in my native clay, anyway. It is hard as a rock when dry, and mucky gucky when wet and sweet peas would choke in it. I have read that sweet peas also prefer a “limey” soil, but our soil is already naturally alkaline.

Sowing the seed
Although many people enjoy starting seeds directly in their bed, and you can do this with sweet peas, my personal preference is to start in pots. I like this because I can control their growing conditions more, and I don’t have to go outside to check on watering every day. You can start your seeds inside or outside. I start mine inside since I have a shelf with lights for other seed-starting projects.

Many people recommend chipping or soaking seeds before sowing. I chipped my first batch of about 20 sweet peas and they germinated in 1 week. You can do this by clipping a small amount on the seed with a nail clipper. Another perhaps easier way would be to use a nail file to lightly file down the outer coat of the sweet pea. Go easy on this, you don’t want to file too much, just enough to allow the moisture to penetrate the seed past the hard seed coat. However, neither of these methods are necessary; they will germinate eventually, albeit more slowly. I sowed a batch of sweet peas without any soaking or chipping. They germinated here and there from 10-25 days, and if that irregularity doesn’t matter to you, sow them as is.

Sow sweet peas an inch down into soil, and keep them moist until they germinate. If you want to grow them in containers and give them extra oomph, sow them in “deep root” seed containers. There are a few of these on the market now; they are seed-sowing pots made specifically for plants that like to have ‘long roots’. If you look at a young sweet pea seedling root, it is usually very long and thick.

After they germinate
Once the plants have at least 1 set of true leaves, fertilize them with a dilute solution of all-purpose fertilizer, or a seedling fertilizer. I use a mostly organic fish emulsion-based fertilizer in both my garden and on seedlings.

If you are growing them in pots: After they have about 2 sets of leaves, I usually bring my seedlings outside so they can adjust to the weather. Whether you’re growing inside or outside, wait until the plants have at least 3 sets of true leaves before you plant them. This gives them a chance to grow some nice roots and get a head start before they jump into the soil. This also keeps them from becoming victims to critters that like peas and will happily chomp on small seedlings but are not so interested in larger plants. I have squirrel problems here; they like to pull up just about everything but especially seedlings.

Many instructions say to pinch out sweet peas after their second true set of leaves, so that they can develop side branches. I did this for many of them, but found that it’s not necessary, as the plant will eventually produce side branches on its own. Usually the main stem withers after awhile, whether you pinch or not, so in general you are more interested in using the side shoots to tie up.

Sweet peas need more water than most of the cool-season annuals, and they will let you know it when they don’t have enough. They start to wilt. The way I check is putting my finger down the soil a few inches or more. If the soil is dry, I water.

Tying up vines
In early spring, the plants will start sending very stout shoots that are much thicker than the seedling shoots. These are the ones you want to tie up, unless you like the look of wild vines running around your garden or growing through shrubs. Sweet peas in spring quickly become a tangle of long vines and tendrils. Some kinds grow as high as 10 feet here, some may stay around 3 feet. (This doesn’t include dwarf kinds or “Cupid”, but even those can get tangly if you don’t arrange and trim them when they start getting really big.)

Once the first strong side shoot is about a foot long, you’ll want to tie it in place–either to a trellis, some netting, an arbor, or a fence. Sweet peas have curly tendrils a lot like passionvines and sometimes they help themselves up but much of the time they meander off all over your garden bed. I’ve tried all kinds of trellis options–including netting that I set up across a garden bed with bamboo poles. It’s not the prettiest of growing conditions, but they will need something to climb on, so make sure you have this climbing structure in place before you plant the seeds.

If your bed is well prepared, you shouldn’t need much fertilizer. I like being organic, and I use a diluted fish-emulsion fertilizer to water in all my transplants, whether annuals or perennials. My beds have a good mix of compost in them to begin with (something you must do anyway where I live, to loosen up clay soil).

But I am not an expert on fertilizer. Keep your soil healthy; the best way to know what your soil is and needs is by having a soil test done. In Austin and much of Texas, we tend to have very alkaline soil which sweet peas actually prefer. Go easy on those weird “super bloom” high phosphorus fertilizers; I learned by getting a soil test that I had naturally very high amounts of phosphorus (it gets tied up in alkaline soils). A balanced one is best, or better yet, get a soil test.

Once they bloom
There is nothing like seeing your first sweet pea bloom. If you’ve tried winter-blooming kinds, they will bring a rare fragrance to the winter blues. Don’t forget to pick them and often. If your vines get to the point where they start producing seed, they will slow down or stop producing flowers altogether. Once they open, sweet pea blossoms usually last 3 or 4 days at most, and by then they have started to self-pollinate and produce seed. I usually walk through my garden at least once a day and keep scissors with me to trim things, and during the bloomiest part of spring I was picking sweet peas nearly every two days.

And alas, the dreaded Powdery Mildew and other problems
Powdery mildew is the bane of sweet peas. If you’ve never seen it on roses or other bushes, it looks like its name–a white powdery film on the leaves, both top and bottom. Unfortunately, since we grow them here in the most humid time of year, they are particularly susceptible to powdery mildew. Some of mine got it worse than others, but not a single plant didn’t catch powdery mildew.

I have to say I haven’t quite figured how to successfully battle it other than start spraying plants before it catches on. Usually by the time a plant has powdery mildew it can spread really fast to other sweet pea leaves.

Other problems can battle sweet peas, and often I have a few that just never grow, shrivel up and die–their leaves stunt or curl, or turn yellow. In these cases, I am assuming that some kind of rot or fungus has gotten them. I try not to get discouraged!

It’s fine to snip off leaves that are really ratty. You can also thin them out if they are becoming really bushy and tangled; this lets air move around the plants more. I’ve tried baking soda and soap sprays, baking soda and garlic tea sprays, milk and water sprays and even some organic ready-made products. Like any other part of your garden, don’t spray for pests or fungus in the heat of day but early in the morning or at sunset. Go lightly with anything that has cinnamon, orange or neem oil in it, it can burn the leaves if not done properly.

It also helps to avoid watering plants from overhead (using a drip or soaker hose system), and making sure they stay well-watered. Drought stress and/or overwatering stress actually contribute to a plant succumbing to problems like powdery mildew.

Saving for next year
Sweet pea seeds can actually be saved and resown. If you decide to let one plant go to seed, watch for the “pea pod” that emerges from what was the flower. It looks a lot like edible pea pods (but some warn that these are toxic to eat). Wait until it dries and the ‘peas’ rattle in the pod, just as you might do wtih bluebonnets. I have stored sweet pea seeds in my fridge for two years and they are still viable.

For a suggested list of sweet pea varieties to try in Texas, try these two pages:
about winter-blooming sweet peas
Sweet Peas in my garden

13 Comments Post a comment
  1. Thank you for your very informative article. I have such fond and vibrant memories of my parents’ sweet peas I just had to try to grow them. It’s so hot here and I really don’t have a good place for them in the ground, so I planted the seeds in a 25 gallon container. “Necessity is the mother of invention” …no truer words were ever spoken! The vines are tall and growing on a obolisk I had. So far, so good! Question: how long before they will bloom? They have seed pods forming and some seem ready to open, but nothing yet! I planted the seeds in January and want them to bloom before the vines get too hot and die.

    Thank you for your help.

    Rosemary E. Vaughn
    Zone 8

    April 8, 2012
    • Amy #

      Rosemary, I know this has been a long time since you posted, but in case you get this message, if you want sweet peas in your zone, I highly recommend planting them NOW. If you get frost, and I’m guessing you do (what state?) you want them in a bit earlier than frost or they’ll get bitten. I’ve tried planting them later than December but they turn out quite small in the spring and don’t quite have the root system to take off in the short time that they can bloom here. They really start dying off after it goes over 80 degrees. In Austin (which is more like zone 9), my window of bloom is between March and April. The early blooming types can start as early as December or January but they have to be in the ground by September to do that. Hope that helps!

      November 6, 2012
  2. linda talley #

    thanx so much for info on sweet pea growing; i live
    south of New Braunfels and planted peas for the 1st time: vines grew well, few blooms, something
    nibbled on leaves; looking fwd to trying again as love them…..linda

    May 11, 2012
    • Amy #

      thanks! aren’t they pretty?

      November 6, 2012
  3. Sean Cavanaugh #

    I, too, have had all my sweet peas affected by powdery mildew. This year was probably the worst. I found some good tips for eradicating and controlling powdery mildew at the UC Davis website:

    Thank you for the growing tips. In my native Montana, we didn’t have to do anything special to grow spectacular sweet peas other than sow the seeds. Alas, in San Diego, they require a lot more care, but like you, I feel they’re worth it.

    June 12, 2012
    • Amy #

      Hi Sean! Yes, some years are worse than others. It’s unfortunate, because they really need rain, but the more it rains the worse it gets! After a point they all get it, when it really starts getting hot and humid. I’ve tried a lot of different sprays and usually at some point I just give up and smell the flowers ;). They’re one of the shortest lived flowers in my garden but they make me so happy!

      November 6, 2012
  4. Roger Collins #

    Thank you for your informative article about the cultivation of sweet peas. I came upon it after a ‘Google Image’ search. Although I have been gardening now for about forty years I have not grown sweet peas for a long time and I was a little worried about my two trays of slightly pale and very leggy specimens which are sitting on my windowsill at the moment. At first glance I was stunned. Beyond your window I could see trees in sunshine and full leaf. Have I sown them far too early, was my immediate thought. Here, the weather is still a little frosty and, although I have plenty of daffodil shoots poking hopefully through the soil, the only plants at present in flower in my garden are some tiny purple irises. Then I realised. You don’t live in England! Austin, Texas is a long way from Bury St Edmunds in Suffolk. Nevertheless, although your advice may not be entirely relevant to my situation, I was heartened to learn about someone else in the world who is trying to cheer up their little patch of the planet.
    Well done and thanks. Roger Collins.

    February 24, 2013
    • Amy #

      Hi Roger, these pictures were probably taken in an April (it has been awhile since I wrote this so I can’t quite remember!). I have read that some English gardeners start their plants in fall and keep them protected through the winter. They will probably get a little leggy on a windowsill as they do like lots of light. I’d guess that in your climate, you could plant them in spring after frost has passed. They usually take about three months from seed to bloom. I must plant mine outdoors in fall, because our summers are too hot and we do not get freezes. Graham Rice is one of my favorite UK gardening authors and he wrote a wonderful practical book about sweet peas that could give you some good planting ideas. Perhaps you can find it in your library? I hope you had success with your sweet peas. Aren’t they just lovely? They are my favorite annuals!

      July 2, 2013
  5. Hello! I want to plant sweet peas, but it’s February. Do I need to wait until next Fall?

    February 27, 2014
    • Amy #

      Hi Emily, I’m sorry to be replying so late. I have tried planting them in February but it does not give them enough time to establish good roots and flower. November is my absolute latest and usually they struggle to get big enough if I plant them even that late. They are usually done flowering in late April, or as soon as the first 90° week sets in… I’m assuming you’re in Texas–sweet peas have different growing times in other climates. I hope this helps!

      March 19, 2014
  6. Emily #

    Hey, yes- I’m in Austin actually.

    I never planted but I have seeds. I ordered from owl acres in the UK.
    What do I do with my seeds since it’s too late?

    Will they last until the fall?
    I’ve read you can refrigerate?

    Or should I soak them, nick them, and hope for a spring miracle?

    I’m considering all possibilities! Just let me know if the seeds will keep til the fall and how to store them. Thanks!

    April 2, 2014
    • Amy #

      Hi Emily, yes you can refrigerate as long as they are sealed or kept away from moisture. Sometimes I put them in a bag with one of those silica baggies that come in shoe boxes–the silica keeps them dry. That’d be the best strategy. But I’ve left them out for a full year in a box on my shelf and they germinated just fine the following year. I definitely wouldn’t plant them now. Sweet peas are pretty predictable in how they grow. In the perfect growing and germinating conditions, it would take about two weeks to germinate, and then another 6 to flower. And by then they are only about a foot high. By June it is just way too hot for them in Texas. My best sweet peas ever were ones I sowed in early September. They germinated by October… and I had some sweet peas as early as Feb. 1!

      April 3, 2014
  7. Emily #

    How long do unplanted seeds last? I don’t really have a yard to plant them in and I only have containers. Can they be grown in containers only?

    October 7, 2014

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