The Problematic Primrose

baby primrose (Primula malacoides)

baby primrose (Primula malacoides)

Few plants are as pretty or as problematic as the primrose.
The primrose (Primula spp.) takes an honored place among those plants that are beyond compare when at their best but, in general, are somewhat pitiful to look at. This is because proper conditions for their growth usually are lacking.
We all have experienced the frustration of picking out some ravishing beauty of a plant in the nursery, only to see it transformed into a pathetic botanical specimen soon after taking up residence in our garden. This commonly happens with plants that require a constant feed of minerals or an acidic soil – plants like gardenias, azaleas and hydrangeas.
All of these plants, like the primrose, are notorious for developing chlorosis. Chlorosis is a physiological disorder that results from a mineral deficiency in the plant. Where iron deficiency is the problem, new or terminal leaves turn yellow, even as their veins remain green. (This condition is sometimes referred to as interveinal chlorosis.)
Chlorosis occurs where the soil has a high pH or is overly compacted or waterlogged. Minerals with a high pH, such as lime, hold onto molecules of iron and prevent them from being absorbed by plant roots. Iron is an element that plays an important role in the processes of photosynthesis and chlorophyll formation. Without iron, a plant’s production of sugar – its source of food – will be curtailed and the chlorophyll which makes plants green will not be synthesized.
In compacted or waterlogged soils, beneficial oxygen-loving (aerobic) bacteria are replaced by anaerobic bacteria. Anaerobic bacteria turn nitrate into ammonia. When nitrate – which is the form in which nitrogen is absorbed by roots – is not available, plants cannot form chlorophyll and leaves become yellow.
Primroses succeed in the Pacific Northwest, where the soil is acidic due to heavy annual rainfall. Rain leaches alkaline minerals – that bind iron in our desert climate – out of the soil, lowering the pH and allowing primroses to thrive. Primroses, like azaleas, grow best in soil that is 100 to 1,000 times more acidic than that found in Los Angeles.
Primroses grow best in a mixture of peat moss, well-drained topsoil and completely decayed compost. Ideally, you would build raised beds or planter boxes that contained these three materials in equal amounts. If you are preparing a new or worn-out area for planting, keep spading and mixing in peat moss and compost until the soil grade has risen four to six inches. After planting, mulch with more compost.
It is preferable to use homemade compost, whenever possible. Composted sewage sludge products, sold in nurseries under an assortment of labels, are increasingly popular due to the need for recycling municipal waste. From my experience, though, I have found homemade compost – made of shredded leaves, grass clippings and steer or horse manure – to drain better than composted sludge. This is important where primroses are concerned since they are killed by soil fungi that thrive on excess moisture in the earth.
Three species of primroses are commonly seen in local nurseries. Primula polyantha, the English primrose, is one of few plant species that produces flowers of virtually every color. Whether your passion is for red, yellow and blue or for pink, sulphur and purple, you will find your favorite combination of colors among the English primroses.
Primula malacoides, the fairy or baby primrose, has strictly pastel blooms in the pink to lavender range. Less showy than the English primrose, it is a fine subject for clay pots on your shaded balcony or patio.
Primula obconica, a rhizomatous species in similar pastels, is not always available, even though it may bloom longer than either the English or the fairy primrose.
If primroses do not succumb to chlorosis or soil fungi, they must still be protected from snails and slugs, which find them a tantalizing delicacy. Shredded bark or leaves, on top of your compost mulch, should be an effective deterrent.
Primroses are naturally associated with the subject of color for winter shade gardens. They are, in truth, perennial plants and will survive from one winter to the next as long as they are planted in the right spot – under a deciduous tree – in the right soil and kept properly mulched throughout the year. The shade of a deciduous tree will protect primroses from drying out in the summer (excessive dryness kills them). By dropping its leaves as winter approaches, this same tree will allow in the light needed to form primrose flower buds, which should open up around the first of the year.
Where color for winter shade is a problem, consider planting cyclamen, another member of the primrose family.

Photo credit: Nemo’s great uncle / / CC BY-NC-SA

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