Growing double primroses
Double primroses have a reputation for being difficult. There are some things to think about, but they are no more difficult than many other plants.
Vine weevil This is a constant worry. I try to keep plants separate for a time after I receive them in the hope that if they have vine weevil I can spot it and they don’t have a chance to get at my other plants. I was treating with Provado Vine weevil every four months as a preventative, but now I use nematodes.
Moisture They like to have a damp spot (not water-logged). They will not be happy if they are too dry. The flowers on some doubles, especially the tighter doubles, do get spoiled by persistent rain and these I tend to grow in pots and give protection from rain when they are flowering so I can enjoy the flowers. Generally, it is best to grow them in a damp, shady spot so they don’t get too dry in the summer.
Cold Especially a concern if you are growing the primroses in pots. Although they are hardy perennials if they are in pots and freeze you are likely to lose them. Give them some protection in winter. But do not molly-coddle them excessively. Get the pots outside if you can for the rest of the year; they do seem to prefer this.
Feeding The old books always suggest a good diet of well-rotted horse manure. I live right by a dairy farm so the primroses that I grow in the ground get large quantities of cow manure dug in around them. If you are growing in pots don’t forget that the nutrients in the potting compost will get exhausted and you do need to feed.
Attention Keep an eye on your plants. If you are growing in pots remove decaying leaves to minimise risk of fungal infections, lurking slugs, etc. Remember that a pot is not the plant’s natural environment, and it will need a bit more care. Check that the plants aren’t pushing themselves out of the ground. They do seem to have a tendency to push themselves upwards. Check that roots are sufficiently covered by soil.
Propagation I propagate through division. Plants will deteriorate as they get older and you will lose them if you don’t divide them. Some varieties are slower growing than others, some will want dividing every year. Plants naturally grow sections that can be split off and you will soon see when this is possible. If your plants look like they are “going backwards” divide them and remove any carroty roots (old woody roots). This photo shows a bad case of carrotty root and you can see the plant pushing itself out of the ground. new roots are visible at the top of the carrot. The carrot can be broken off and the plant replanted. It should then grow away vigorously again. Sometimes it is possible to lay the carrot horizontally in a seed tray of compost and get new plants to grow from it. It doesn’t always work, but it is worth a try.