How to Grow Sweet Peas (Even if You Live in the Desert)
Introduction to Sweet Peas
Sweet peas are one of those flowers that are popular with just about everybody.
I think it’s partially because they are spectacular flowers, coming in a wonderful array of colors and that wonderful scent - heady and sweet and somehow amazingly luxurious in their olfactory profile -
I think it’s because of that magical scent (since scent is one of the most powerful senses, especially as far as memories go) that people also have very strong memories (and therefore strong feelings) regarding sweet peas. Usually memories of a wonderful parent or grandparent that grew sweet peas.
Either way, sweet peas give everyone the warm fuzzies, but they’re also a great cut flower to grow because they’re extremely productive, has a beautiful flower that works into just about any sort of floral design and are surprisingly tough as nails despite their rather fluffy and delicate appearance.
They’re also easy to grow so long as you follow a few rules and understand what they need which in a nutshell is:
Warm dark conditions to sprout
Cool bright conditions for growing on into fully grown plants
Warm bright conditions to flower with plenty of water and nutrients to flower
How to Start Sweet Peas from Seed
Growing sweet peas is actually easy once you demystify the process. Sweet peas are actually pretty tough plants and are one of the easiest cut flowers to grow so long as you get a few points down.
Buy high quality seeds
Generally speaking, the best sweet peas come from high quality sources. They perform the best, give the best flowers and perform the best. We only grow Spencer varieties - the multi-bloom ruffle-edged gloriously beautiful sweet peas that are the only choice for floral design. Other sweet pea varieties are OK - the multifloras, semi-grandifloras, grandifloras and old-fashioned varieties are certainly still beautiful and are especially great in the scent department - but make for better ornamental garden plants as opposed to cut flowers.
Start them off in big and tall pots
Sweet peas have big and long root systems with a big and long taproot that grows deep. This is a good thing as far as the plant goes (helps them to establish themselves quickly and readily, even makes the vines pretty drought tolerant) but it can cause some difficulty when you’re starting them from seed.
Some people grow sweet peas in specialized pots known as “Rootrainers” - each individual cell has long and grooved sides to encourage the roots to grow down, perfect for growing sweet peas in - but we found them to be a bit cost prohibitive so instead we just started our sweet peas in a large 4” pot (that is also around 3.5” tall just like the Rootrainers).
You can see here that we sowed them thickly - they’ll grow in as a large mass - which works well in conserving seed starting space. It won’t hurt them to sow them this densely because we’ll separate out the plants later on - this is just a temporary holding container for them.
Plant your seeds deep - they like darkness to germinate
Light inhibits germination of sweet peas, so you’ll want to bury the seeds under the soil (I once made the mistake of trying to start sweet peas in a paper towel on a windowsill - which inadvertently exposed them to a lot of light and so the seeds just rotted). Bury the sweet pea seeds 1/2” under the soil surface- they are vigorous and big seedlings so they’ll push their way up through.
Provide high moisture when germinating
Sweet peas have a big and thick seed coating so they need the humidity to soften the coating so the sprout can break through easily. If you don’t have a high level of moisture, your sweet peas may end up being stunted or not end up germinating completely since a dry environment can cause the seed coating to be too constraining.
Start them off on heat
While sweet peas really like to grow on in cold or cool conditions (30-50 F) for best growth, they will take forever to sprout at that rate. In fact, I would venture they won’t germinate at that temperature and would instead end up rotting.
Instead, start your sweet peas at a higher temperature. We place ours on a heat mat at 75 F and they sprout up in a few days. No fuss and pretty uniform germination and you’ll see them all sprout up pretty quickly.
Then Get Them Off the Heat Quickly
Once sweet peas start germinating, they’ll grow very, very quickly. It’s important not to let your sweet peas transform into thin, leggy, pathetic seedlings that are floppy and fragile - you want your sweet peas to grow into short and squat and robust seedlings.
High temperatures will encourage legginess, so you’ll want to get them to a cooler environment (30-50 F) as soon as they start germinating. Which leads us to our next section…
Growing Out Sweet Pea Seedlings
Okay, so now you’ve got sweet pea sprouts. Now what?
It’s time to grow them out a little bit before planting them out in your garden or into the field. Sweet pea seedlings generally take us a long time to grow out from sprouts to young plants- we’re talking three to four months during the middle of winter - but again they are actually surprisingly tough plants once you get them grown out.
Move them out to cool and bright conditions
Sweet peas grow best in cool and bright conditions. They can take a bit of frost or freezing conditions, but generally speaking they grow best (and most quickly) when temperatures are a bit above freezing ( a constant 50 F would be ideal).
You want them to stay cool because it will encourage them to grow good root systems - slowly but surely they will grow them - and it will prevent the young plants from getting leggy and floppy. Leggy and floppy sweet peas don’t really transplant well - the stems can break and they are more vulnerable to injury and disease - so we want to again aim for short and squat and robust seedlings.
Bright light conditions are also important so that the young seedling can get light to photosynthesize and feed this short and healthy growth. If not given enough light, the seedlings will be sad and chlorotic and will also be leggy and floppy.
So how do you create these conditions? There are a few ways to do this:
1. Grow in a cool greenhouse or hoop house
This is the ideal situation, in which you can control the temperature of the growing environment and provide the maximum amount of light possible. If you’re a flower farmer, chances are you have this setup. No need to provide additional heat for your sweet peas at this point - grow them low and slow.
2. Grow in a sheltered outdoor location
If you don’t have a greenhouse or hoop house, you can still grow sweet peas outside if you have a relatively mild winter and can shelter your sweet peas from too much extreme weather and wind (this is how we grow our sweet peas out).
We have a courtyard that is walled in on four sides and provides a nice little microclimate for our plants. It’s just a little bit warmer and a little bit more sheltered than the rest of our property, and allows for our sweet peas to grow slowly and surely over the winter.
They might get a bit cold - maybe upper twenties - but if it gets super cold we’ll throw a bit of floating row cover over them to keep them warm. Cold really doesn’t bother sweet peas too much. The main issue is with wind - a cold and powerful wind can really dry out your sweet peas and cause wind damage to their foliage. If you don’t have a nice wind shelter, you can insulate them with a structure like a low tunnel, straw bales, or even just put cloches or covers over them.
3. Grow in an unheated garage or structure under artificial lighting
This is a strategy many flower farmers use to get sweet peas started because it allows for an easy alternative to a green house or hoop house. By setting up shop lights on wire racks you can grow out hundreds of seedlings in a very small space.
We used to grow sweet peas in this way and it works great - the sheltered indoor environment means less fussing compared to growing them outdoors - and it’s a nice area to hang out in away from the cold and wind when you’re in the middle of winter.
On the other hand if you’re growing a ton of sweet peas, this may not be the most efficient way to do so due to space constraints. So unless you have a huge building or are not growing a ton of sweet peas, I’d recommend another method.
A Note on Fall Planting Sweet Peas
Some flower farmers will actually start sweet peas in September or October and plant them out into the ground to allow them to overwinter like a perennial plant.
I had mentioned previously that you could use cloches or low tunnels to grow out your sweet peas and if you have a milder winter you definitely can do this. While I wouldn’t suggest doing this if you’re in a growing zone 6b or lower, if you can provide protection through low tunnels with either plastic or row cover on top of them, this will allow for the most vigorous and earliest sweet peas.
We did this the past year and found that it was actually quite easily. I started our seeds in October, planted them in the ground in November and then covered them with floating row cover until April. I checked periodically underneath to ensure they were doing OK (they did just fine) and they started to take off mid-April.
Planting Out Sweet Peas Seedlings
Sweet pea seedlings are quite sturdy seedlings when grown properly, and are really easy to handle. We plant ours out during a warm week (that’s not going to be dropping down below freezing) just reduce the chances of a cold shock.
Add an organic fertilizer to the soil
Sweet peas are heavy feeders and since we don’t produce a ton of compost in our garden (see: high desert location) our sweet pea beds get some compost that we haul in as well as some organic granular fertilizer to ensure they get a steady supply of NPK all season long. This is all mixed into the bed before we start planting (and actually well before we put the beds to rest for the winter).
Plant them a bit deeper than the pot
Sweet peas will actually root all along the stem if allowed, so we plant ours so that the top set of leaves are just poking out of the soil. Which actually isn’t much - we sink them down about an inch or two - and they stay nice and sturdy and happy this way.
If your sweet pea seedlings are a bit leggier and taller, I would recommend trying to bury at least halfway up the stem - this will reduce the legginess and allow you to have a greater stability for the plant.
Make sure to also handle them via the leaves - grabbing by the stem bears too high a risk of breaking off the stem and stunting or killing the plant.
Water them in well
Even if its cold outside, you’ll want to ensure that you water them in well. The roots will need to have a good moist soil to start growing outwards into, and if that soil is dry your sweet peas won’t grow a good root system into the surrounding area, instead just staying within their little bit of potting mix you’ve planted them in.
A good deep soak is best when planting initially, allowing the water to fully penetrate the soil. You’ll then be very hands off with the water (during winter they don’t need a lot) until the plants start growing
Cover them with row cover
Personally we use floating row cover as opposed to plastic - it’s much more manageable and is much more hands-off compared to plastic cover - and it works well to protect sweet peas from extreme cold and wind.
We’ll even double up the floating row cover if we need to, since an additional layer is like putting on another jacket and keeps the plants just that much warmer.
You can remove the covers as needed once the weather starts to warm up…
Sweet peas tucked under row cover for the winter. The fabric is light and allows for the transmission of air and is “breathable” while still keeping them a bit warmer and moister than the open field
Getting Sweet Peas to Bloom
Sweet peas are what are known as daylight sensitive plants that need a certain number of hours of daylight to start blooming.
For the Spencer varieties we grow, it’s around 12 hours of daylight that they need in order to start blooming. Some, such as the early multiflora varieties (the ‘Sunshine’ and ‘Winter’ varieties) will bloom with as little as 10 hours of daylight and are perfect for greenhouse production or just early sweet peas in the garden if you’re growing in the more northern latitudes.
It’s our job to ensure the plants keep growing and are in good health prior to them starting to bloom - we want them to have plenty of leaves and stems to allow them to have a lot of structure to photosynthesize before producing flowers, because big and healthy plants will allow them to produce more and bigger and more beautiful flowers.
Feed and Water Regularly
We have a drip irrigation system setup for our sweet peas, so watering is a simple matter of just hooking up the hose. If you don’t have a drip irrigation system, you’ll have to water by hand - drench the base of the plant with water and to avoid getting water on the foliage so you don’t cause fungal diseases.
We also supplement with an organic water-soluble feed. Alfalfa tea works well for nitrogen, while we’ll also utilize kelp fertilizer to ensure they get some micronutrients as well.
During the cooler months, we feed about once a month. But when the plants start growing (I swear, they grow a couple inches a day once spring starts to warm up!) we’ll feed once a week to ensure they have the nutrients they need to grow and produce well.
Provide Them Support
The traditional way of growing sweet peas is with a trellis or lattice framework that they can grow up. Some enthusiasts go as far as to stake each plant individually with a bamboo or hazel cane that they will then tie the vine up against.
While this is the way to go if you live in a cool and northern climate where you can properly grow sweet peas, for us our sweet peas don’t necessarily need a trellis or support since they grow rather more like bushes or a groundcover than vines (our temperatures and days cause them to start blooming at just 12” tall) - more on this in a bit.
Most people use Hortnova netting stretched between supports for their sweet peas - it’s affordable, easy to setup and easy to tear down once you’re done with them (you just cut it from the supports after the season is over). However we’ve also seen chicken wire as well as cattle fence panels used for the trellis which while significantly more work to setup would provide a more permanent matrix for your sweet peas to grow on.
It’s important that your netting or trellis is attached to sturdy supports. Those vines weigh a massive amount when fully grown, and poorly attached netting (or weak supports) will mean your sweet pea vines will one day just collapse onto themselves (and there’s no coming back from that). T-posts or solid wood stakes pounded into the ground are the standard for netting supports, but you can go even further and build a structure out of 2x4’s if you have to.
However you decide to support your sweet peas, just make it sturdy!
Keep the weeds down
Weeds will start to pop up around your sweet peas because they’re vines, and although sweet peas aren’t easily choked out by weeds it’s still a good idea to keep the weeds down so they don’t compete for moisture, nutrients and light.
We actually have taken to doing what is known as an underplanting of other flowers at the base of our sweet peas to shade out and out compete weeds, as well as being more efficient with our space and allowing for us to hide the sometimes unsightly bases of the sweet pea vines that can unfortunately start to yellow and dry as the plants mature.
This year we’re growing Icelandic poppies as the spring underplanting - both plants like the same conditions, bloom at relatively similar times and conditions, and can be removed at about the same time of the year as well (early summer). We’re going to follow it up with a succession planting of celosia and cosmos later on, but the Icelandic poppies are a perfect companion to the sweet peas.
The Icelandic poppies (the lighter green plants) are under planted at the base of the sweet peas. Both will bloom at the same time, and the Icelandic poppies help to reduce weed competition by shading out any weed seedlings
Keep Up with Tying Up Your Sweet Peas
Although sweet peas can and will grab onto the most basic supports with their tendrils, it’s important to ensure that you keep them attached to your netting or trellis in order to help them keep climbing firmly upwards.
We recommend tying them to your support by the use of a Velcro tape for plants - you can cut off the correct sized piece and loosely attach the vine to your support. Don’t crush or compress the stem, just tying loosely (but firmly) to the support should be enough.
Harvesting Sweet Pea Flowers
As the spring goes on, you’ll start to see the vines start taking off. They’ll get big and thick stems with huge fleshy leaves, and that’s when you know that things are going to happen.
If you live in a more northern location with fewer hours of daylight, you’ll see your sweet peas grow into larger plants and vines before seeing flowers.
On the other hand if you’re like us in a more southern location with longer hours of daylight earlier in the season, your sweet peas will grow more like bushes and start flowering when very short.
Either way, you’ll soon start to see flower buds starting to form in the internode areas of your vines. They look like little teardrop-shaped pods at first, but they’ll start to fill out and you’ll see the buds start to swell as they start to mature.
The buds will then start to develop even further until the actual flower pokes out of the bud and you can see the colorful petals hanging down.
When to Harvest Sweet Peas?
Sweet peas flowers will open starting with the lowest bud at the base of the stem first. We harvest when that bud is just starting to open and before the top bud has had a chance to open up yet - this allows for the greatest vase life since you get to start the vase life from the time the lowest flower starts blooming until the top flower finishes blooming (which can be quite a long time - a week for us in some cases).
How to Harvest Sweet Peas
We harvest during the coolest parts of the day - early morning and late evening - and cut the stem all the way back to the vine. They immediately go into water to ensure they get hydrated as soon as possible.
I personally like to carry a mason jar filled with water and a pair of snips - this makes it easy to pop the cut stems of sweet peas into a small container without them getting crushed or knocked out of the water.
How to Condition Sweet Peas
Sweet pea flowers generally need just cold and clean water to hydrate well. They’ll keep well in a floral cooler, and so long as you keep them away from fruit (the ethylene gas from ripening fruit causes the sweet peas to go over very quickly) you should get a good 3-5 days off a large sweet pea stem with multiple blooms.
Ideal Growing Conditions for Sweet Peas (and what to do if you don’t have ideal conditions)
The ideal conditions for growing sweet peas include long and mild summers - New Zealand and the U.K. and San Francisco being some of the ideal growing environments where the sweet pea vines can grow and reach 10 feet tall, covered in long-stemmed blooms that go on for months and months (in essence if you never get much beyond 80 F during the summer - an AHS heat zone 1 - then you’ll be able to grow beautiful sweet peas in the garden. Alternatively, we have flower farmer friends that live in very hot zones that grow their sweet peas in the winter in heated hoop houses - in essence recreating the summer environment in an AHS heat zone 1 - but if you’re without one don’t fret - you can still grow sweet peas just fine)
So what happens if you don’t have ideal growing conditions for your sweet peas? What happens if you’re in a place like the Midwest with cold winters and hot humid summers and a short period of spring in between?
Or, what if you’re like us and live in a high desert environment - high desert meaning that we still get all four seasons (including some sow and freezing temperatures) as well as hot and dry conditions in summer with almost no spring.
Not exactly the ideal conditions for growing sweet peas!
What ends up happening when you grow sweet peas in non ideal conditions is that they don’t form quite as big of a root system and so you get smaller plants with smaller vines and they start blooming a lot sooner (see my previous comments regarding day length and temperatures)
Our sweet peas don’t grow big and tall Although we do get healthy, vigorous growth, our sweet pea vines hardly get beyond a couple feet long before starting to bloom. And while they continue to bloom for a very long time, the actual stems of the flowers are relatively short - about 6-8” long
While I used to get frustrated regarding our short sweet pea stems, as it turns out it wasn’t such a bad thing.
You see, sweet peas do relatively well in the vase when harvested into cool water. But we found out a method of harvesting sweet peas that allows us to grow them successfully as a cut flower even while living in a hot and dry environment that is just about as non ideal for growing sweet peas as possible! (Takeaway: if we can grow sweet peas successfully, so can you).
What to Do with Short Sweet Pea Plants?
Although we’re all familiar with the gigantic tall sweet pea vines that grow to massive lengths, there are a variety of sweet peas that is available known as dwarf sweet peas. Meant originally for bedding plants and container or hanging basket flowers, they actually make a surprisingly good cut flower.
Despite the fact that their stems are very short, the dwarf sweet peas are very prolific, forming a little bush covered with blooms - great for a bedding plant but hardly the long elegant stems that you would need for a bridal bouquet or centerpiece.
On the other hand, using short stems is my specialty - since everything we grow in our high desert growing environment is on the shorter side - and through a little experimentation and creativity, we found that we could use these short blooming plants for floral design.
Additionally, the short stemmed, short blooming Spencer sweet pea varieties that we grew were also suddenly very usable despite their short stems because we started harvesting more than just the sweet pea flowers - we started harvesting the whole vine!
Sweet pea flowers when cut with a bit of the vine attached (4-6” or so) actually last a lot longer and have a longer vase life than when cut on the stem. It’s a really cool idea that I learned from a veteran flower farmer growing in a high desert environment (who would grew thousands of sweet peas and would harvest them on the vine for their lucky florist customers to use in arrangements).
This is perfect for us because our sweet peas bloom on shorter (but bushy) plants. It solves a couple issues for us
A shorter vase life for sweet peas (which can be a concern for some people) is helped out by the extended vase life when cut on the vine
Shorter stems - which happen either in growing zones that heat up very quickly in the spring such as for us here (or alternatively happens as you near the end of sweet pea season in cooler zones) - aren’t an issue if you cut the vine as well
You have added value now with the bit of vine added to the flower because it’s a flower and a foliage rolled into one. The broad leaves and airy tendrils are a delightful textural contrast to the big blowsy flowers
How to Grow Sweet Pea Vines
Growing sweet pea vines are no different than growing sweet peas normally, but it comes with one major (and positive!) difference - you don’t have to attach them to a trellis or netting.
You see, when you’re growing sweet peas for their vines you don’t need to worry about them having something to climb on. Instead you can let them sprawl out since you’re going to be cutting the vines back (and preventing them from getting too unruly).
Now, I do like to kind of keep them corralled, so I have a single wire or string that runs the length of the row that allows the sweet peas to cling with their tendrils into it. It isn’t enough to keep them necessarily as upright as netting, but allows them to stay relatively upright - and makes for easy harvesting (I can simply unwind the tendrils from the single wire) while untangling sweet pea vines from netting can be quite a pain in the you-know-what.
Keep your sweet peas well watered and fed (the same you would if growing for flowers) and they’ll grow a prodigious amount of vines and buds.
The single line of string helps to keep the sweet pea vines relatively upright and makes it easier to harvest
How to Harvest Sweet Pea Vines
Of course with as vigorous as sweet peas are, the plants won’t miss a bit of the vine (a few inches) snipped off. You’ll set them back a tiny bit, but it ends up just making the plant that much more bushy, producing even more vines that you can then cut. And once sweet peas start blooming, they will continue pumping out vines and blooms.
If you’re a gardener growing sweet peas to enjoy in your home, sweet pea vines make floral designing so easy - you just cut a handful of flowering vines, arrange them into a vase and you’re good to go!
On the other hand if you’re a flower farmer that’s looking to sell your sweet peas, I’d highly recommend you try harvesting them with a piece of vine so that you give an extended vase life. And if you’re selling to florists, they will an absolute hit with them - you won’t be able to grow enough of them.
If you’re growing sweet peas for your floral designing needs, sweet peas on the vine are going to really change the way you design with them. They are a great way of extending the lines of your design by allowing the vines to trail over the edge of a container or swirl and twine around an arrangement, which makes for some super fun designs! And of course, you can always use them as you would a traditional stem by cutting them and inserting them as a straight stem.
I’ve even taken to cutting and using the vines occasionally as foliage (sans flowers or buds) because they are such an elegant and excellent foliage. The vines and foliage itself is very long lasting - up to a week - so can be used accordingly if you need it. '
Cut them and get them into water ASAP, stripping off the lower leaves to expose the stems and allow them to hydrate. They store well in the cooler, but can also be arranged into water right away as well.
