Monday, May 15, 2017

Primroses


I've grown several forms of Primula over the years. Sometimes with success and sometimes not. Those successes and failures have slowly taught me what most Primula need to do well in my gardens. What I learned was that most like gritty well-drained soils, cool temperatures, good fertility, and consistent moisture. While this is a generalization too broad for a genus of over 400 species and countless hybrids, it fits with many of the types readily available in garden centers. Having had success with several types now, I decided that maybe it was time for more varieties.

P. Pacific Giants Mix
Recently I put out a request for reliable sources for Primula seed on Facebook, and my friend Amy kindly offered to send me some seed if I just donated postage to the American Primrose Society. I expected maybe 5 or 6 packets of seed. When the envelope arrived, I opened it to find 19 packets of seed for a wide range of different species and varieties. Postage was $.98. I messaged Amy and thanked her for her generosity, but told her I couldn't donate just a dollar to APS for such generosity. She agreed that APS membership was a suitable payment, so I joined.

P. 'Blue Zebra'
One of the neat things about the APS is that they've been around since 1941 and publishing a newsletter since 1943. Most of those newsletters are available to the public on their website. That's over 70 years of journals about the genus! I also picked two new books. One, The Plant Lover's Guide to Primula, is great for anyone who wants to learn more about the genus from a gardeners perspective. The other, Primula by John Richards, is the definitive work on the genus and is probably best for hardcore Primula lovers and other botanically oriented people. Both are excellent books that I'm excited to have added to my library.

I want to share a bit of information that I've learned over the years and recently in my reading. The APS journals and my new books have helped clear up some terminology that I never really bothered to delve into before. As is often the case, what's often advertised in garden centers and box stores isn't necessarily correct or complete information. I also want to share how to grow some of the readily available types I've sold and grown over the years.

The most common type you find for sale at garden centers usually are labeled as P. vulgaris or P. polyanthus. These are not true P. vulgaris, but are hybrids involving P. vulgaris, P. elatior, P. veris, P. juliae and others. Polyanthus isn't actually a species, but rather a descriptor of flower type. They are popular spring flowers in garden centers and usually found as mixes like Crescendo, Pacific Giants, or Supernova. Sometimes you can find them as specific colors from the series (ie Crescendo Blue Shades). Each of these series are slightly different, and all are very hardy - usually to z3.

There are two basic ways the flowers are held on this group of hybrids. Polyanthus types have a cluster of flowers on a stem. The mentioned series above all fall under the Polyanthus group as do the species P. elatior and P. veris. Acaulis types have flowers that are held on stems individually, and many varieties fall under this category such as the Belarina series and the species P. vulgaris.

These plants are all pretty easy to grow, which is one reason they're so popular. They like a woodland soil which is well-drained to prevent being waterlogged in winter but with plenty of organic matter for moisture retention during the growing season. They also do best with some afternoon shade and can't be allowed to dry out in the summer. I've grown a lot of these. I've also killed a lot of them, but I have a pretty good handle on keeping them happy now. In my case, improving the drainage of my clay loam with pine bark and making sure I watered them regularly was the key.

P. elatior

P. veris
P. Supernova Blue


P. Supernova Purple
P. Supernova Mix

P. Supernova Mix

And acaulis type Primula

P. Belarina 'Valentine'
P. Belarina 'Cobalt Blue'

P. Crescendo White

P. Crescendo Yellow and Crescendo Red

P. Crescendo Blue
P. Crescendo Mix
An acaulis type Primula
Primula denticulata is the first species that I really had good success with. It likes similar conditions to the previous group: well-draining woodland soil and a little extra irrigation in summer. I found the species to be a little more forgiving about surviving summer dryness, but it's naturally found in fairly moist sites. This species blooms about the same time as the vulgaris hybrids, but grows a bit taller - up to a foot. The foliage can get quite large after blooming if the plant is happy. It tends to be  vigorous species growing two feet across or more and can self-sow around the garden if conditions are good. The dense spherical clusters of white to purple flowers make this a really popular species.

P. denticulata
P. denticulata
 Primula seibodii comes from Japan and is also quite popular and quite a diverse species. Flowers can look like typical primrose flowers or be really finely divided and range from white to magenta to purple. This species likes plenty of organic matter and seems to like being consistently moist all season. If it gets too hot or too dry it will go dormant in summer, but usually emerges again in fall. Like other primroses, despite wanting consistent moisture during active growth, it needs well-drained soil to avoid rotting during dormancy.

P. sieboldii

P. sieboldii
P. sieboldii 'Petticoat Junction'

P. sieboldii 'Petticoat Junction'
Primula japonica falls under the candelabra group of primroses. The candelabras tend to have taller flower stems with whorls of flowers at the top and along the stem. They like similar conditions to the P. sieboldii: organic rich soil that stays consistently moist in summer. P. japonica is easy to grow in these conditions and will happily seed around creating a nice colony. Flowers tend to be magenta, but can also be found in red, white, and light pink shades.

A red form of P. japonica

Several other candelabra primroses are popular and readily available including P. beesiana with its pink to lavender flowers; P. bulleyana which features gold to orange flowers; and a slew of hybrids involving P. bulleyana, P. beesiana, P. cockburniana, and P. pulverulenta.

The alpine primroses are another popular group and includes several species and hybrids. The one most popularly available at retailers is Primula x pubescens, which is a hybrid involving P. auricula and P. hirsuta. This group also includes the Auriculas, which are border and show primroses that are some of the most popular plants among Primula enthusiasts. 

The alpine types tend to have leaves that are much more fleshy than other types of primrose. Like other types they are heavy feeders and appreciate plenty of organic matter, afternoon shade, and consistent moisture. But having alpine origins they also really appreciate well-drained soil. These are best suited to rock gardens and raised beds with some sort of gritty soil mix. I didn't have good success with P. x pubescens until I planted it in a bed that was about 50% crushed granite, 25% soil, and 25% organic matter. I also had a plant tight up against a large silver maple. The ground was raised around the root flair and the soil drained quickly there and that plant also did really well.

P. x pubescens

P. x pubescens
Hopefully some of the above information will help you out if you've never grown Primula or if you've struggled with them in the past. If you enjoy growing primroses and aren't yet a member, consider joining the American Primrose Society

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