Wednesday, March 12, 2014

Primula Odyssey

When I moved to Michigan on a day much like today (snow in March), I had left behind a California garden full of succulents and tropical plants like fuchsia and hibiscus.  Now it was time to regroup.  I studied the English cottage garden (always an ideal) and prepared to grow herbaceous borders.

Browsing through the seed packets at the garden store, I found Primula veris.  I had read about primroses in English gardens so decided to try it, though it looked difficult.  Two years later, I was enchanted.  The plants grew vigorously, self-seeded, and helped to make spring cheerful and light.  That was the beginning of an odyssey into understanding and growing this genus.

A classic polyanthus. I call this one "Old Yellow".
The most familiar Primula are the polyanthus "primroses".  These are hybrids and many selected varieties exist.  The flowers are held on a stalk, usually above the leaves.  Actually, these are not true primroses.  Botanically minded gardeners sometime refer to them as Primula X polyanthus to indicate that they are hybrids.

Primula vulgaris "True Blue"
The true primroses are Primula vulgaris, a European species that is well known as an English wildflower (but apparently much less common in the wild now).  The flowers are not mounted on a stalk, but arise singly from the crown of the plant, thus are sometimes referred to as "acaulis",  "caul" referring to a stem.  The classic P. vulgaris is a lovely creamy yellow (the color sometimes called "primrose").  But there are many color variants that have either occurred naturally or through hybridizing with garden plants.

But the genus Primula is not limited to our familiar garden plants.  Primulas exist in the wild all over the world, though the single species in South America is likely a modern introduction.  I can make this statement because I possess the most authoritative book on Primula in existence and it describes the range and distribution of the genus. The book is Primula, by John Richards (Timber Press).  Anyone who has become as obsessive as I have about primulas should have the book, which describes the history, distribution, and biology of the genus, as well as its taxonomy.  There are also a selection of color plates.  But for a really wide selection of pictures of primulas, see Pam Eveleigh's gallery of Primula species  (she uses Richards' taxonomic scheme).  As Richards makes clear, the overwhelming majority of primulas are from Asia, or as he puts it, "the eastern Sinohimalaya".

Candelabra primulas
Fortunately, the English, being great plant explorers, brought many Asiatic species home and they are available to gardeners.  The candelabra primroses are descended from those early collections.  They have been hybridized and released as special varieties, which are usually grown in sweeps together. But the species are still grown. The plant blooming to the left is Primula burmanica. Primula helodoxa is just visible to the right.  The hosta behind them is full-size; P. helodoxa is very tall.  The Asiatic primulas appear to require continual seed-harvesting and replanting.  For that reason, there are not many left in my garden.

Primula auricula
Another species that has been widely adapted to gardens is Primula auricula.  There are some varieties that are spectacularly colored, so that they almost appear to be from outer space.  They are usually grown in greenhouses and brought out only for flower shows.  But there are garden auriculas too. Note that the foliage is quite different from the other primulas shown.

Primula juliae
Primula juliae is not only a long-lasting and enjoyable garden subject, but was also the source of some of the colors now available in polyanthus.  It has a different growth habit, creeping to form a little colony over time.

Having grown, loved and lost a number of primulas, I've come down finally to concentrating on those I know will have some staying power in my garden.  They include my faithful Primula veris, the acaulis P. vulgaris types,  P. juliae, and the endless varieties of polyanthus. But probably I'll always be tempted by another challenge to engage more primulas.

This polyanthus is of the true "primrose" color.

Note: this article follows another one on primulas, Primula Fever, which describes more primulas and their hybrids and has more pictures.

Sunday, March 2, 2014

Winter Dreams

So how does a gardener survive winter?  Especially such a long and cold one (Michigan has been in the path of the "polar vortex" and has received more than 40 inches of snow so far this winter).

The first line of defense is, of course, the garden catalogs.  This is the time to pour over the pictures and imagine a garden full of every delightful plant possible.  I find myself dwelling over Johnny's and wondering why I can't grow exotic varieties of vegetables that I've never even eaten.  My particular obsession is with lettuces - nothing more beautiful than lettuces like blooms on the soil, especially to my winter eye. Seed catalogs often tempt one to over-order but there are also stalwarts that simply must be obtained every year.  I have a number of favorites that my garden would miss if I didn't order them.

But the consequence is that the seed packets arrive in the mail, and many of them need to be started indoors.  This is a benefit.  It is an opportunity to work with living things and see the green of chlorophyll in spite of the snow cover.

The techniques of seed starting can be very simple or extremely complex.  Most garden plants have been selected over hundreds of years to be started easily from seed.  Wild or recently domesticated plants often have dormancy mechanisms that need to be overcome before the seeds will germinate.  The survival value of this is obvious.  Seedlings may be killed in one year's bad weather and others can germinate in a different year to flower and set more seed.  Here is a discussion of factors that inhibit germination.  Here is a master list of conditions for seed germination in many wild species.

Even easy garden plants have requirements. Seed germination requires several environmental triggers to be present, and the combination of these varies somewhat from species to species.  First, water must be present.  Even dead seeds will soak up water (imbibition) and it is the first step in germination. Light and temperature are the other two triggers.  The right combination, and sometimes the right sequence, will cause a complex series of hormonal changes in the seed that allow the embryo to grow and use the stored food reserves.  Here is a scholarly review of the physiology of seed germination.

For the great majority of garden plants, higher temperatures (around 70° F) are best for germination.  This can be supplied by "seedling heat mats" for sale in many garden stores and catalogs.  There are also many light fixtures for growing plants (fluorescent lights are best) that can be fancy or simple.  I use shop lights propped up on blocks.  It is necessary to keep humidity high while germination occurs - this can be with plastic domes, plastic bags, or even transparent sweater boxes.  A timer should be used to turn lights on and off.  I use a 14-hour day length.

Seedlings are easily killed by a couple of common fungi.  This is called "damping off".  For that reason, seedlings should be started in sterile artificial medium, typically sphagnum peat that has been finely milled.  The germination medium I use also has vermiculite added to keep it from clumping.The medium should be kept damp, but not flooded.  I use a plastic spray bottle to keep dampness at the right level.

Clean containers should be used to start the seedlings.  I use simple plastic trays (and plastic bags in the beginning).  But there are many "seed starting systems" for sale.  The trays last for decades and I clean them with bleach before use. 

Most seedlings should not be transplanted until they have developed some true leaves. For most garden plants, the first "leaves" are the cotyledons, which had been the location of stored food reserves and then become green and photosynthetic after emergence.  The seedlings are still very young and don't have much of a root system yet.

Later, the true leaves have developed and the plant has begun to grow.  Eventually it has become time for what the British refer to as "pricking out" - transferring them to single containers.  I prefer 4-cell packs which allow more root room than the 6-cell packs many commercial growers use to sell flats of annuals.

In the cell packs, the plants can grow under the lights, and later be moved outside.  I use a cold frame to temper them until it is consistently warm enough to plant.  But they'll last in these cell packs until June or later.

ADDENDUM: A question left unanswered here is, "When should you start the seeds?" This depends on your location and the first frost-free date for your area. In Southern Lower Michigan, it is approximately May 15, so vegetable seeds should be started with that in mind.  Johnny's Select Seeds has a handy seed-starting calculator for that decision.   Flower seed starting is variable: some need to be started as early as January in order to bloom in a reasonable time after they are planted out. Petunias take a very long time to become planting size, for example.  Hot-weather annuals like zinnias and marigolds will need to be held until the frost-free date, so that should be taken into account.  Some others, like pansies and violas, can be planted earlier so should be started earlier.  Perennial plants often grow slowly so benefit from an early start.  The seedlings shown above were all planted this year (2014).  A cold frame is useful to temper seedlings in the couple of weeks before the frost-free date.