When the Allionii primulas finish flowering it is usually time for to start the annual potting on. The plants may not necessarily have out grown their pots but the organic matter in the compost decomposes and reduces the air content available to the roots, and that usually spells disaster for alpine plants.
The Allionii primulas are always first on the list for they produce a abundance of new growth immediately after flowering, before taking a little rest in the summer and then making a further surge of growth in the autumn. If they are not potted on immediately you stand to lose most of the new growth as the nutrients in the compost are all used up at this stage.
That is one of the reasons they are first on the list. The other reason is that they are in the larger of the pots, and this gives me a better idea of how many new pots I will have to purchase.
By starting with the large pots and working down through the range of plants I can re-use the Allionii pots for Androsaces and the Androsace pots for Dionysias and so on down the line.
The Allionii primulas are the most difficult to handle because the leaves are very brittle and sticky and the slightest mistake leaves you with a sticky mush covered with soil. I usually let them get fairly dry before potting time and the soil falls away without many problems. If the soil is wet at this stage a lot of the roots can get broken and recovery can be slow in the new compost, it can even lead to rot setting in, as the roots cannot take up as much moisture as before.
A large batch of compost is prepared beforehand by mixing two parts J, Innes no 3 (a soil based compost with all the necessary nutrients added) one part leaf-mould, one part sharp sand, one part horticultural grit, one part perlite, and one part vermiculite. A shake of insecticide powder for the vine-weevils and a shake of Osmocote slow release fertiliser and the compost is complete.
This is not the usual compost that I use for potting the Allionii, but the plants are now going into 30 cm pots which means they are getting rather large and drainage in more important.
