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How to Grow Sweet Peas – The Answer!

How to Grow Sweet Peas – The Answer!

Part of the thrill of gardening is constantly learning about new plants, and getting to add them to your plant collection. 

To keep your garden looking colorful, one flowering plant you should consider adding is sweet pea. 

Featuring a rainbow of colors and intoxicating scents, it’s a must-have for any gardener who loves sprucing up their homes with flowers. 

Sweet pea has a bad rep for being difficult to grow. But as you’ll see from our article, you only need to master a few tricks in growing sweet peas like a pro. 

Read on to learn more about caring and growing for the sweet pea plant. 

 

 

How to grow sweet peas?

Growing sweet peas in your garden requires the right preparation before the planting process itself. To start off, you should nick the seeds first for faster germination. Next, you’ll need to choose the right medium where you’ll plant the sweet peas. Once done, you sow the seeds with a 1-inch depth and 2-3 inches spacing between each seed. Water the seeds gently using a watering can. But, if you’re using a hose, make sure you use the gentlest stream possible. Just make sure to place a net over your sweet peas to protect them from birds or other animals that like to munch on them.

 

Step-by-Step Guide to Sow Sweet Pea Seeds

 

Nicking

The first thing we recommend doing is nicking your sweet pea seeds.

Although this is not something that’s mandatory for every plant, we encourage doing it for this crop because it improves the germination rate and duration. 

From first-hand experience, nearly all my nicked sweet pea seeds germinate and they do so within a short time. 

To achieve this, look for a sharp knife, nail clipper, or razor blade and hold it with one hand. Hold the seed on your other hand, between your forefinger and thumb. Then, clip the seed. 

Be careful when nicking these seeds. You want to slice through the seed’s top layer, not cut out a huge chunk of it. 

You might not be able to see the specific spot that you slice through. Other times, a portion of the seed cracks off, revealing the light-colored inner seed. Either way, it’s fine. 

 

Choose the right medium

Sweet pea thrives in a medium that is well-draining and fertile. As explained later in the article, it’s good to prepare the seedbed beforehand by working in aged manure or finished compost. 

Before you start sowing, also remember to rake the area so that it’s completely uniform. Next, look for a stick or tool that can help you dig small furrows. 

Sweet pea seeds ought to be planted to a depth of 1 inch, so you’ll want to make sure the furrows aren’t too close to the surface.

 

Sowing

And now to the fun part! Bury your seeds in the furrow, leaving a distance of between 2 and 3 inches between them. 

Sowing your seeds with such gaps increases the chance of getting a voluminous bed of plants with zero spaces. 

But once your seeds sprout, you’ll need to thin them out to their last spacing. 

After sowing, cover the furrows by pulling soil over them. Move just a tiny amount of soil. 

It should be enough to cover the seeds but not too much that the seeds get pushed deeper into the ground. 

 

Watering

The next step is to water. It’s important that you water your newly planted seeds very gently. 

If you’re too aggressive, the top layer of soil will get washed away leaving the seeds exposed. 

To avoid this, I like to use a watering can which releases a small stream of water. If you opt for a hose, then ensure it has an attachment to help you control the water flow. 

At this stage, it’s also good practice to put up an anchor to support your sweet pea plant once it matures. Research shows that most species grow up to a height of 2m. 

 

Protecting

The last thing you want to do before heading out is to verify whether your sweet pea seeds are protected. 

It’s crucial to consider this as early as you sow, otherwise, you might find that the seed got swept away by rain or eaten by common predators like snails, slugs, and birds. 

To protect against birds, consider adding a net over the area. Polytube, the flexible plastic tubes often used for irrigation, would be perfect for this application. 

You can get this from a local garden store near you or improvise one. 

For snails and slugs, experts recommend using Sluggo Bait. This is a natural pesticide, effective against slug and snails. 

The best part is that it’s non-toxic; hence, safe to use around pets, people, and wildlife. 

 

Starting Seeds Indoors

If the weather isn’t too friendly, you may be thinking about starting your seeds indoors, which also works. 

However, you’ll have to acclimatize your seedlings before transferring them to the garden. This means giving the seedlings time to get accustomed to the outdoor conditions, typically, direct sunlight, fluctuating temperatures among others. 

Failure to harden off your seedlings may result in transplant shock. This means that the young plants become too stressed under the new conditions that they fail to develop healthily. 

Begin the acclimatization as soon as the seedlings start forming 3 to 4 pairs of leaves. Once this happens, transfer your plant to your designated spot outdoors. 

Ensure it gets a bit of exposure to both the morning sun and afternoon shade. 

If you don’t have such a spot where the plant won’t be exposed to direct sun rays, you can transfer it outside in the morning, then take it back indoors when the sun gets too intense. 

After 4 days, transfer it to a permanent location so that it gets sun all day long. Better read an article on light levels so you’ll be better guided on this.

 

Sweet Pea Profile

Scientifically, sweet pea is known as Lathyrus odoratus. It’s mainly grown for its blooms, which not only come in a variety of colors but are also very fragrant. 

This plant has tall vine-like stems, which extend at least 6 feet. It is from these stems that compound leaves emerge, each bearing two ovoid leaflets and a tendril. 

The flowers can take on many colors, including white, red, pink, purple, and violet. 

While the sweet pea produces seeds as well, these are mostly inedible. 

In fact, eating these seeds in excessive amounts can trigger Lathyrus. Lathyrus is characterized by difficulty in breathing and convulsions. 

But for the most part, sweet pea is a highly beneficial plant, rewarding you with rainbow colors and beautiful scents. Let’s look at how you can grow sweet peas.

 

How to Care for Sweet Pea

 

Soil

Before planting your sweet pea seeds, it’s wise to work the soil first. This paves way for the soil to process organic matter; hence provide the plant with necessary nutrients when the time comes. 

Once you have the perfect location for planting, dig the soil down no less than 1 foot. Next, apply a generous amount of compost or aged manure.

Speaking of location, you’ll want to choose an area that has well-draining soil. Or if you’re planting in a container, be sure to choose a well-draining potting mix. 

This is where most people go wrong. Just because sweet pea fares in cool climates doesn’t mean you should flood it with water. 

It’s highly susceptible to rotting, so it’s best to use soil that drains water effortlessly and fast. Leave water sitting at the base of this plant, and chances are, it won’t survive.

This explains why it’s recommended that you sow its seeds in mid to late fall. By then, the soil is workable thanks to the evaporation that occurs in the earlier, warmer months. 

 

Watering

On the surface, watering may seem like a trivial part of taking care of your sweet pea. 

But, there’s a lot that goes into this task, ranging from the frequency to timing, depth, surrounding climate, and more.

We’ll start off with the frequency, which is about once a week. During the growing season, however, you should water as often as it takes to keep the soil consistently moist but not waterlogged. 

The watering frequency will also depend on what growing medium you’re working with. If the soil is one that drains overly fast, you’ll likely have to water often. 

Alternatively, consider adding mulch to such soil to boost its moisture-retention capabilities. 

I like to mulch regardless of the soil I am using for my sweet pea. This is because mulching also keeps weeds at bay. My mulch typically consists of grass clippings or weed-free straw. 

Experts also recommend that whenever possible, water your sweet pea during morning hours. This gives the vines ample time to dry out in the afternoon. 

If the vines are still wet or damp by the time the sun sets, they run the risk of getting fungal infections.

 

Temperature

When sowing sweet pea seeds, the ideal temperature of the soil should be ranging between 55 and 65°F (13°C to 18°C). 

Like other crops in the pea family, it thrives in cool weather. For the best outcome, ensure the temperatures remain below 65°F (18°C) for at least 50 days. 

 

Fertilizer

The sweet pea plant doesn’t require too much fertilizer. In fact, if you go overboard, you will end up with a plant that has plenty of deep green leaves but only a few flowers. 

In terms of type, a well-balanced 20-20-20 fertilizer gets the job done. You can also opt for organic fertilizers, which is what I prefer. 

Now, the best time to apply this fertilizer is during planting time. After that, you only need to fertilize once per two weeks. 

 

When to Plant

Sweet pea is a cool-weather crop, and this means it’s never too early to start sowing its seeds. 

Although a few varieties of this plant are grown in warm climates, most species thrive in the cold. 

So the best time to sow is when the ground is still cool to touch, preferably with a temperature of 40 to 50°F (4° to 10°C). 

In USDA planting zones, the perfect time for planting is between late October and mid-November. 

You can also extend this to December but only if you live in an area that doesn’t experience hard frosts. Otherwise, the roots will never grow. 

 

Which Sweet Pea Variety Should You Grow?

Sweet peas can be categorized in four different ways: by habit, flower structure, scent, and day length response. 

For habit, it can grow into a compact or a climbing structure. Climbing sweet peas wind themselves around a support frame and can grow between 6 and 10 feet tall. 

For compact varieties, they only grow to about 24 inches tall. 

Based on flower structure, some sweet peas have single flowers, meaning they have a specific number of petals. Others have double flowers, meaning they have twice the number of petals.

On the same point of flowers, some varieties tend to have stronger scents than others. 

Here are a few examples of sweet pea species:

 

Apple Blossom Sweet Pea

This is a climbing plant that attains a height of about 6 feet. Given its blush-pink petals, which give off a deliciously sweet scent, the Apple Blossom would make a great addition to a flower border. 

 

American sweet pea

Discovered back in 1896, the American sweet pea is one of the most fragrant varieties. You can easily identify the American sweet pea with its creamy-white flowers with crimson red accents. 

It’s a climber, which grows up to 5 feet.

 

Black Knight Sweet Pea

Originating from the Mediterranean region, Black Knight is an annual, trailing plant. With its deep burgundy-purple flowers, it’s great for adding contrast to a garden or flower arrangement. 

It’s also strongly scented, meaning it can easily attract bees, butterflies, and other insect pollinators.

 

Cupani Sweet Pea

One of the earliest varieties of sweet pea, Cupani was discovered back in 1695 by Father Francis Cupani. 

This species is as fragrant as it is attractive, bearing gorgeous, violet and deep crimson blooms. 

This sweet pea is often confused with Matucana, which has similarly colored flowers. However, Cupani produces just two flowers per stem while the latter bears four flowers.

 

Chatsworth Sweet Pea

If you’re looking for a Sweet Pea that is not too pronounced, Chatsworth is your best bet. It has subtle lavender florets, which are borne on long stems. These flowers are mildly fragrant.

The plant was first showcased at a National Sweet Pea Society event that was held at Chatsworth House; hence the name. 

 

King Edward Sweet Pea

If color is what you’re after, this sweet pea species fits the description. Its flowers have a beautiful crimson color that makes them stand out in any space. 

They’re also fragrant and can grow throughout summer and extend slightly into autumn. This sweet pea is also a little taller than the rest, growing up to a height of 6 feet.

 

Lipstick Sweet Pea

Like the King Edward, the Lipstick variety is also quite tall. So much so that it can grow as high as 7 feet.

The flower stems are long too, averaging about a foot high. They bear 3 to 4 flowers each. 

These blooms are strongly scented, and have a bright red hue.

 

Matucana Sweet Pea

As we mentioned earlier, the Matucana bears a striking resemblance to Cupani due to the mix of burgundy and purple flowers. 

Another trait that makes this sweet pea unique is its outstanding fragrance. 

In fact, some gardeners believe that it could be the most scented sweet pea. Matucana can grow up to 8 feet tall and thrives in full sun. 

 

Tips to Grow Sweet Pea Problem-Free

 

Choose the right sweet pea variety

There are two main varieties of sweet peas: annuals and perennials. 

The annual, which goes through its life cycle in a single growing season, is the more preferred type. Scientifically, it’s referred to as Lathyrus odoratus.

The perennial is known as L. latifolius. Save for the continuous growing seasons, it shares fairly the same traits as the annual one. 

The problem with perennial sweet peas is that they grow invasively. They can cover open fields and roadsides within no time, denying surrounding plants of essential resources. 

 

Time your planting season right

As we mentioned earlier, sweet pea prefers cooler temperatures. 

You have the option of starting your plant from seed, or purchasing starter plants then transferring them to an outdoor setting after the last frost. 

Here are some tips to help you with the timing:

  • Start your seeds indoors either in early spring or late winter (this should be 8 to 10 weeks prior to the last frost date).
  • In early spring, you can also sow the seeds directly in your outdoor garden (preferably 6 weeks prior to the last frost).
  • In autumn, the best approach is to sow directly outdoors; this particularly works for areas that experience mild winters where the soil doesn’t freeze.

 

Prep seeds before planting

If you’ve never sowed sweet pea seeds before, then one thing you should know is that they have a tough exterior. 

This can get in the way of germination, especially if you’re in a hurry. So to hasten the process, you can either nick or rough up the coat; hence, boost water penetration.

This is only necessary for seeds that are started indoors or sowed in spring. 

If you’ll be planting outdoors in autumn, there’s no need to take these steps because Mother Nature will naturally assist with that.

Two of the most common methods of preparing seeds are:

 

  • Rubbing the seed coat with sandpaper or a grater. You can also nick it with a small nail clipper, which is what I do. 
  • Alternatively, you can soak your sweet pea seeds before planting. Place them in a damp kitchen towel for no less than 12 to 24 hours. You can also soak them in a container filled with warm water for at least 8 hours.

Soaking the seeds is an easy way of softening that hard shell. But, don’t go overboard, otherwise, the seeds will become mushy. 

 

Sow your seeds to the correct depth

I cannot emphasize enough how important it is to sow your seeds to the right depth, that is, 1- to ½-inch deep. They should also be spaced no less than 4 inches apart. 

If you bury them too deep, they won’t access essential resources; thus, fail to germinate. 

On the other hand, if you place them very close to the surface, they may dry out or worse, get destroyed by critters. 

 

Add the trellis during planting

A lot of gardeners forget to do this when they’re planting their sweet pea seeds. 

While it’s possible to add later on, setting up the support system beforehand minimizes its chances of destroying your delicately maturing plant. Plus, it’s much easier to erect it before a mature plant grows.

Wondering what trellis to use? Here are a few suggestions:

  • Chicken wire
  • Long bamboo poles
  • T-posts
  • PVC pipe
  • A-frame

In the first couple of weeks, you will have to guide the vines along the trellis. Inspect the vines on a daily basis. This way, they don’t end up wandering off or wrapping themselves around.

After all the effort you’ve put so far, the last thing you want is to have a tangled mess that you cannot sort out. 

 

Deadhead flowers

One thing I like about the sweet pea plant is that it produces long-lasting blooms. But, ultimately, the flowers dry out and transform into seeds. 

When this starts to happen, consider deadheading old flowers. Look for aged blooms on your plant, follow its stalk downwards up to where there’s a set of leaves. 

Trim the flower just slightly above the node (the point where the leaves intersect with the stem).

 

Common Sweet Pea Problems and Pests

 

Damping off

Many gardeners have encountered this issue when starting their sweet peas from seed. 

So what exactly is damping off? 

This is when your sweet pea seedlings seem totally healthy, and then suddenly start wilting and die for no apparent reason. 

The main cause of this is a fungus, which grows when there’s excess moisture and both the temperature of the soil and the atmosphere are higher than 68°F (20°C). If you experience this issue, there’s a good chance that the soil is too wet.

To prevent it, keep the seedlings moderately moist but not waterlogged. Also, do not over-fertilize and always thin out the seedlings so you won’t have problems with overcrowding.

 

Fasciation

Put simply, this is a deformity that strikes sweet pea stems. It causes them to grow too big or flatten unusually so that they appear as if they’re fused. 

This condition, which is caused by either a virus or bacteria, penetrates through wounded parts. To prevent it from damaging your crop, handle your sweet pea with care, especially when you’re transplanting.

Also, don’t cause any injuries by pruning excessively. You will also want to ensure that you’re getting your plant from a reliable supplier, who deals in pathogen-free plants. 

 

Root rot

Caused by a soil-borne fungus, root rot is another issue that’s common among sweet peas. The first sign you’ll notice is yellowing around the plant’s base. 

This will be followed by the withering of the stems, and eventually, the plant will die. 

Thankfully, this is one problem that you have great control over. Start by checking that the soil you’re using for your crop is well-draining. 

If the soil is too dense, then add some coarse gravel for improving the drainage aspect. 

Secondly, ensure there’s enough spacing between your plants. Finally, buy seeds from a reputable supplier or ones that have been treated with a fungicide to minimize the risk of rotting. 

 

Pests

Although regarded as hardy, the sweet pea is vulnerable to several pests. In particular, there are certain insects that get very attracted to the flowers’ scent and vibrant coloration. 

Here are the most likely pests you’ll find, and how you can best address them:

 

Aphids

Certain aphids species are attracted to sweet peas more than others. These include potato aphid, light green foxglove aphid, and green peach aphid. 

When they attack, they pierce the plant’s stems and leaves, then start drawing sap. Unfortunately, these insects are very tiny, making them difficult to spot with the naked eye. 

The best you can do is watch out for signs such as:

  • Distorted and discolored leaves
  • Stunted growth
  • A sticky residue of honeydew

Keep in mind that aphids may also be carrying diseases, which could prove fatal to your sweet pea plants. 

To be more specific, they are carriers of enation mosaic, and pea mosaic viruses, which can lead to plant death if left untreated. 

Consider inspecting your crop at least two times each week. Check whether your plant is showing any of the signs mentioned above. 

If your plants are in an outdoor setting, then weed the area on a regular basis. Aphids are good at hiding in clumps of weeds, so do not entertain any unwanted vegetation. 

On the same note, avoid fertilizers with high nitrogen content as it fosters aphid reproduction. 

In case the aphids have started attacking your sweet peas already, spray them with insecticidal soap or neem oil. You can also introduce natural insect predators like lacewings, parasitic wasps, or lady beetles.

 

Leaf Miners

These attack sweet pea plants the same way aphids do. Essentially, they prick the leaves and petals, releasing sap.

Once this happens, the leaves become mottled and fill up with white spots. It gets worse if you’re dealing with a full-blown infestation, which results in stunted growth and leaf drop. 

If you notice a few infested leaves, remove them immediately to stop the infestation from spreading. You could also introduce Diglyphus isaea wasps, which prey on these pests. 

 

Thrips

The Western flower thrips is another invasive insect that can wreak havoc on your sweet pea vegetation. 

They like to prick the buds, newly-formed curled leaves, and other concealed parts of your plant. 

What’s unfortunate is that adult Western flower thrips take on a wide array of colors, which makes them difficult to identify. The coloration ranges from somewhat white to yellowish-orange to almost dark. 

An easier way of identifying an infestation is to look for signs like black flecks of their feces, discoloration of the plant tissue, and distressed leaves. You will notice leaves starting to fall immaturely. 

Should you notice any thrips infestation signs, take action immediately. You can spray your sweet pea with insecticidal soap. 

Or, you can introduce natural predators, such as parasitic wasps, green lacewings, and minute pirate bugs.

 

Frequently Asked Questions about Growing Sweet Peas

 

How long does it take a sweet pea plant to bloom?

With most varieties of sweet pea, the flowers appear for at least one month during spring. That said, there are some things you can do to extend its blooming period. These include deadheading, increasing exposure to daylight, and enriching the soil with organic matter like compost. 

 

Can sweet pea survive frosty weather?

Unlike most plants, this flowering crop can survive a light frost. As long as the weather doesn’t turn to extremes, your sweet pea plant will do just fine. However, if the temperatures rise too high, this can compromise its flower development.

 

How can I harvest sweet pea seeds?

Start by identifying the specific varieties you wish to duplicate. Take note that only heirloom species are capable of reproducing to their true versions. Now, when you’re out in the garden deadheading flowers, neglect the plants that you’ve decided to duplicate. Instead, let these blooms fade and die while they’re still sitting on the plant. Once this happens, the petals will start falling, prompting the formation of pods that contain seeds. 

 

Which sweet peas are the most fragrant?

If you’re growing sweet pea primarily for the scent, then you’ll probably want to know which species contain strong scents. A sweet pea’s fragrance varies depending on the time of day when you pick the flower, and how old it is. Varieties with the strongest scent include Black Knight, Cupani, Dorothy Eckford, Gwendoline, Matucana, Painted Lady, and Mollie Rilstone. 

 

Why do some sweet peas fail to flower?

If you’ve been waiting for your plants to flower and it’s just not happening, the most likely culprit is limited exposure to daylight. Keep in mind that this crop needs more than 6 hours of daylight. If you’ve placed it in an area that is too shady, think about moving it to a sunnier spot. 

 

Why are my sweet pea leaves starting to turn yellow?

The most probable culprit is overwatering, but there could be other reasons as well. One of these is if you’re watering from a cold hosepipe. Ice cold water can result in root shock or damage. The best thing you can do is to use fairly lukewarm water. Another likely reason is overfertilizing, which can end up burning the root system. This is especially common when too many sweet pea plants are grown in one container. 

 

Conclusion

Native to the Mediterranean islands and southwest Italy, sweet pea is among the most colorful plants you can add to your garden. 

This climbing plant produces flowers in all sorts of colors; from lavender to blue, white, red, and pink.

Sweet pea is not the simplest crop to grow, but it also isn’t the hardest one either, if you manage to stick to a few basic rules.

Ensure you expose it to full sun for at least six hours and plant the seeds in rich, well-draining soil

It’s also good practice to add a nutrient boost and water your plant just enough to keep it consistently moist but not water-soaked.