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Primulas run backwards compared with most garden plants. They do their growing in the cool halves of the year and rest through the heat of summer, which is when everything else is at its peak. Once you see the year that way the jobs fall into place: winter and early spring are flowering, late spring is the working window, summer is survival, and autumn is root growth and the build up to next spring.
The dates depend entirely on your climate, so the calendar below is written by stage rather than by month. Read it against what the plant is doing, not against a diary. The one point to be strict about is the working window straight after flowering, because a division made then roots in cool damp conditions while a division made in the heat of summer usually dies.
| Stage | What the plant is doing | Your jobs |
|---|---|---|
| Late winter, first flowers | Buds opening as soon as temperatures rise above freezing | Clear old leaves off the crowns; start slug watch as buds show |
| Spring, full flower | Flowering hard in cool weather | Deadhead down to the base; water in dry spells; half strength feed in pots |
| Flowering ends | Still in full leaf growth, soil still cool and damp | Plant out pot plants, divide congested clumps, mulch around the crowns |
| Early summer | New roots and leaves on divisions | Keep divisions damp for a month; shade from midday sun |
| High summer | Resting, little or no new growth | Water enough to prevent drying out; do not feed, do not cut back leaves |
| Autumn, cooler nights | Root growth restarts; sometimes a second light flush | Nematode drench against vine weevil; sow seed; tidy dead leaves |
| Early winter | Dormant or slow, buds forming at the crown | Clear soggy debris off crowns; lift pots onto feet out of standing water |
The working window after flowering
Everything structural happens here, in the two or three weeks after the last flower fades. The plant is still growing, the soil is still cool and holds water, and there are months of mild weather ahead for new roots. Miss it and you are choosing between doing the work in summer heat, which loses plants, or waiting a full year.
Work through it in order rather than dipping in and out. Deal with the flower stalks first so you can see the plants clearly, then the pot grown plants that need a permanent home, then the old clumps that need splitting, and finally the mulch and the watering that settle everything in.
- Strip off every spent flower stalk Follow each stalk to the base of the plant and pull or cut it there. This stops seed forming and lets you see which clumps are congested and which have dead patches in the middle.
- Plant out anything bought in flower Tease the pot bound roots loose, plant into shade at the depth it was growing with the crown level with the soil, and water in. These plants are hardy perennials and will flower again next spring.
- Lift and divide clumps two or three years old Fork up the whole clump, pull it apart into single crowns by hand, throw away the woody center and replant the young outer pieces a hand's width apart at the same depth.
- Mulch and water everything in Spread an inch (2.5 cm) of leaf mold or garden compost around the plants, keeping it clear of the crowns, then water thoroughly. Keep divisions damp for the next four weeks.
Getting them through the heat
Summer is not a growing season for primulas, it is a survival season, and the aim is simply that the plant arrives in autumn with its crown and roots intact. Shade from midday onwards is the first requirement, and a mulch that keeps the top few inches of soil cool and damp is the second. Pots are the vulnerable case, because a small volume of compost in a warm shaded corner still dries in a day.
Do not feed a resting plant and do not cut back tired looking leaves. The leaves it carries through summer are what forms next spring's flower buds, and stripping them sets the plant back a full year. Remove individual leaves only when they have gone properly yellow or brown, and pull them off cleanly so they do not rot at the crown.
Watch for wilting that does not recover overnight. In summer that means either a completely dry root ball or roots lost to vine weevil grubs, and the way to tell the difference is to lift the plant and look rather than to water it again.
Autumn and winter, when next spring is decided
Autumn is when primulas rebuild. Cool damp weather restarts root growth, the plant puts on a flush of new leaves, and the buds that will open in late winter are laid down at the crown. It is also the best time to sow seed and the right time to treat containers against vine weevil, whose grubs are feeding hardest just as everything above ground looks fine.
Winter care is mostly about water sitting where it should not. Clear fallen leaves and soggy debris off the crowns, because a wet mat pressed against the leaf bases in still cold weather is how crown rot and gray mold begin. Stand pots on feet so they drain freely rather than sitting in a saucer of cold water, and move the most exposed ones against a wall out of the worst of the wind.
Hardy primulas need no protection from cold as such; they flower in weather that flattens most other plants. What damages them is the combination of wet and cold at the crown, and freeze and thaw lifting shallow rooted divisions out of the soil. Walk round after hard frost and firm back down anything that has heaved.
Keep one page a year: the date flowering started and finished, the date you divided each clump, and which pots you drenched against vine weevil. Within two seasons that page tells you your own working window to within a week, which no general calendar can do.