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.