My Experience Growing Sweet Peas
Updated: Dec 22, 2022
The first year I tried growing Sweet Peas was a fail in the worst kind of way. I did zero research on Sweet Peas and had no idea what I was doing. My first mistake was direct sowing them in late spring. Here in Zone 7b/8a we have HOT summers and sowing the Sweet Peas so late in the growing season doomed them to fail. I have subsequently learned that Sweet Peas don't like heat. In fact, in my zone I could have sown them in Autumn for them to bloom the following spring, and they would have survived the winter.
My second mistake was planting them just like I would any garden pea. I just threw them in the ground and paid no attention to them. This year, I started them in December and January indoors. I experimented with my December (inexpensive seeds) sowing and then used the results from that round to decide how to handle my January (expensive seeds) sowing.
CandyFloss and Castlewellan seeds from Ardelia Farms
To Soak or Not to Soak...
I decided to test out the differing views on whether or not to soak the seeds overnight before planting. I purchases a pack of Livingston Royal Mix Sweet Pea seeds. The seed pack had 64 seeds in it which is a surprising amount considering the majority of Sweet Pea seeds you buy from Sweet Pea growers come in packs of 10.
I was able to soak 32 seeds overnight and not soak 32 seeds, and plant them up on December 24th, 2020 in containers with organic potting mix. I covered the seeds with a plastic bag, and then covered them with a paper bag for darkness. (Sweet Peas prefer darkness for germination)
Sprouts from December sowing getting ready to be potted up
The first signs of germination appeared on day 5 with both groups having 5 tiny sprouts.
At day 9 there was a noticeable difference in the two groups. Strangely, the seeds I did not soak were coming up faster and in greater numbers than the seeds that were soaked.
It is said that Sweet Peas germinate best at 55F and do well growing in temps between 30F-55F. My seeds were started in my house (68 degrees) and then moved to my unheated garage. I am keeping a light within two inches of their tops, and take them out into the sun every chance I get.
On day 17 after starting the seeds the group that was soaked had 21 seeds germinated for a 67% germination rate. The seeds that were not soaked had 24 seeds sprout for a 75% germination rate. I've read that sweet pea germination usually ranges between 78%-90% so this is a bit lower than usual.
Seedlings separated and ready for new pots
Before the seedlings' leaves started to unfurl, I planted them up into their own individual pots. (I used empty toilet paper and paper towel rolls) I want them to focus on their roots and stay as short and stocky as possible. Toilet rolls work well because they are tall which is good for Sweet Pea roots which need lots of growing space.
Sweet pea seedlings spending time in the sun each day
Branching and Pinching
Sweet Peas branch when exposed to cold weather for a sufficient amount of time. If planted in spring, most Sweet Peas don't have exposure to enough cold to branch on their own. Mine have started branching on their own, but if yours don't you can "pinch" them to encourage branching. Pinching is clipping the seedling just above a leaf node; make sure to leave two or three sets of leaves. This encourages the vine to branch. Pinching will ensure you get more blooms from your vines as they flower just once per location on the vine. Another reason to pinch your sweet peas would be if they have become too "leggy" or stretched.
Here you can see the branch forming on the lower right portion of the vine.
Propagating cuttings after pinching
You can propagate your sweet peat cuttings and form new plants. Clip your vine above a leaf node, and then dip the end in water and then in rooting hormone. Clip excess leaves, leaving just the top set of leaves on the cutting. Place your cutting in potting soil, near the edge of the container so that the cutting doesn't get too much water. You can plant several cuttings in one pot. Now you have bonus plants!
Here again we run into mixed information as to when it is safe to plant out your seedlings. Some warn to wait until all chance of frost is past, and others say they can be planted out before your last average frost. I plant to transplant mine two weeks before my last average frost date. Whenever you feel comfortable transplanting them, make sure to harden them off first. Hardening off is the process of slowly exposing your seedlings to the elements before transplanting them into the garden. Seedlings that are used to being in your house, garage or basement will suffer transplant shock if not hardened off.
Start by bringing them outside in a shady/dappled sun area for a few hours at a time. Make sure they are protected from strong winds. Gradually increase the amount of time they spend outside each day and how much sun they get. By the end of a week they should be ready to go in the garden. I will plant mine out around March 15th, which is four weeks before my last frost date. (You can google your zip code and average last frost date to find yours)
I have found Ardelia Farm, Floret Flower Farm and Swan Cottage Flowers to be invaluable resources on growing sweet peas. I recommend reading the blog post on Ardelia Farms' website titled, "Success with Sweet Pea Seeds." Floret has a great article titled "How to grow Sweet Peas," that is worth reading. Finally, Zoe at Swan Cottage Flowers has an article titled, "How to Grow Sweet Peas,"and a stories highlight on her instagram (@swancottageflowers) discussing pinching and propagating sweet pea vines.