A Glimpse into the Garden: January 2014

A monthly gardening update by OSV staff horticulturist Roberta McQuaid

This behind-the-scenes glimpse of the Village gardens will explore a range of topics including what’s growing in our gardens and the culture and history of specific heirloom plants. We hope that you will find this monthly online feature informative and perhaps it will enrich your next visit to the museum - maybe even adding to your own gardening adventures at home.

The winter greenhouse

For approximately seven months of the year a wonderful collection of herbs call the Old Sturbridge Village greenhouse “home.”  Known as “tender perennials,” they are dug from the herb garden and brought indoors because they will not survive a New England winter.  There are some wonderful and very familiar plants in our collection:  rosemary, bay, lemon verbena and scented geraniums are some of my personal favorites. 

Before the interpreters dig up the herbs I always ask that they give them a bath of sorts to cut down on the number of insects that will be brought into the greenhouse.  For the home gardener this is equally important.  I say “bath” because my pesticide of choice is a natural and fairly benign one, made of potassium salts of fatty acids (soap) that weaken the insect’s outer shell and cause dehydration.  It is sprayed on leaves and stems until they are soaked, and can be reapplied every 7-10 days as needed.  This product is especially effective on insects that make their home on herbs and houseplants:  whitefly, aphids and mealy bugs. 

Once the insects have been eradicated, the herb gardeners get out the shovel and get to work digging up and potting the plants.  Knowing that the first hard frost arrives by early October, we try to get the job done by mid-September.  Most visitors are amazed at how large some of the herbs can become after only a few months in the ground.  It is important to salvage as much of the root ball as possible when digging, so as to minimize the shock of being potted up.  To do this, the shovel is positioned along the “drip line” of the plant and a cut is made straight down, completely around its circumference.  Once this is complete the shovel can easily get underneath to lift the plant up and into a waiting pot.  One that is an inch or two bigger than the root ball is sufficient, and will allow for minimal winter growth.  My container of choice is always plastic, but glazed pottery is fine too.  I steer clear of clay; it dries out too quickly.  I usually put a couple of inches of potting soil into the container, set the plant and then fill in with more as needed before watering well.  Oftentimes I leave the plants outside until a frost threatens, then I bring them in and back out until the weather turns decidedly cold- this way they are better acclimatized to their indoor environment.

Perhaps the most cherished of all tender herbs is Rosemary (Rosemarinus officinalis), the herb of remembrance.  One of the more common questions I get when people tour OSV’s greenhouse in the off-season, is “How do you manage to overwinter your rosemaries?  They are some of the biggest I’ve ever seen!”  In a controlled setting such as a greenhouse, it’s really not that difficult.  Tender plants can be given as much sun as Mother Nature provides, but with the use of thermostats and vents, temperatures can be kept to a minimum.  We set the thermostat at 55 degree night temperatures, and vents open when daytime heat reaches seventy.  Low temperatures like these won’t push the plants into growth when winter day length and daylight can’t support it.  Because of this our plants are stocky, not lanky.  We water when the soil is dry to the touch- sometimes this might be as infrequently as twice a week during an overcast stretch, or as often as every day if the sun is out.  For home culture, a sunny but cool locale is best.   One treat that many gardeners don’t get to appreciate is the beautiful blue flowers that are borne on the plant in the short days of winter.  Legend ties the plant to the Virgin Mary, saying that flowers that were originally white were turned to blue when she spread her cloak on its branches.

Bay tree (Laurus nobilis) is another favorite and can be grown right through the winter with little or no coddling provided it is given medium to bright light and consistent watering.  Do be on guard for the waxy-looking scale insect; one giveaway is leaves covered in a sticky, shiny sap called honey dew.  Try to “Q-tip” individual insects with rubbing alcohol or use insecticidal soap or horticultural oil to smother larger infestations.  If the bugs have been active for awhile, sooty mold may have formed.  This thick, black coating will likely need to be scrubbed off leaf by leaf to allow the plant to photosynthesize properly.

To have success overwintering scented geraniums (Pelargonium spp.) indoors, situate them in bright light where daytime temperatures are 65-70 degrees, and night temps are in the 50s.  Fertilize every other month during the fall and winter.  Smaller leaved varieties will be easier to manage inside; large leaved cultivars will get top-heavy quickly- take terminal or “tip” cuttings of these instead of trying to keep them through the winter. In spring, plant them in the garden once the threat of frost has passed.  Removing yellow leaves during the offseason is a fun “job” as I sniff fragrances like nutmeg, lime, lemon, peppermint!

Lemon Verbena (Aloysia triphylla) may start out looking great, but a month or so into indoor culture will likely begin to lose its leaves.  Fear not, leaf drop is completely normal and to be expected since the plant deciduous!  The plant won’t rid itself entirely of old leaves until new ones push them off in late winter.  You can, at that point in the season, pluck off any that remain.  Breathe deep as you go about this task; here too, the foliage smells great!  With only stems and branches left, give larger plants a good pruning.  Horticultural oil can be of use now as well, this time to smother spider mite eggs.  This pest is especially fond of lemon verbena and populations will spike during the heat of the greenhouse in late spring.  Continue to water the plant as needed as you wait for new leaves to form. 

Soon enough we will turn our attention to seed sowing and the hundreds of transplants that follow.  Until then I will take good care of the tender plants as they eagerly await their return to the garden.

Plant profile: Scented Geraniums

It won’t be long before the scented geraniums will be in full bloom.  Their pastel flowers, in colors reminiscent of Easter eggs, will take center stage among the other plants in the greenhouse.  Here they will bloom happily for several weeks, getting us through the shortest, but perhaps the longest, of the winter months.

I first fell in love with scented geraniums when I was a teenager.  My friend Kelli’s mom had a wonderful collection of them.   In the summer months they took up residence in her herb garden.  During the winter they had a prominent spot in front of her picture window. Gail showed me how to rub the foliage with my fingers to release fragrances like lime, coconut and rose.  It was amazing how close to the real thing these scents were.  Soon, every trip to Kelli’s house involved “catching a whiff” of the scented geraniums before we went off to the business of being teenage girls.

Not long after my introduction to these plants I installed a windowsill shelf in my bedroom and bugged my mother to make a trip out to the herb farm so that I could start my own collection.  It was hard to decide which to purchase.  Besides the fact that each one smelled great, nearly every variety had a different and very interesting type of leaf.  Some were finely cut, like ‘Skeleton Rose,’ others were large and furry like ‘Peppermint.’  ‘Mint Scented Rose’ was variegated, and ‘Nutmeg’ had tiny bluish green leaves. ‘Oak Leaf’ looked very much like its namesake, and even turned red with age!  With upwards of 300 varieties in commerce, it seemed Gail and I were not alone in our admiration for the scented geranium. 

Native to South Africa, the scented geranium made its way to England in the early 1600’s.  Botanists first classified the plant as a geranium, but then reclassified it as a pelargonium (Greek for stork, on account of the shape of its seed).  Although this name change took place nearly three centuries ago we still know the plant as a geranium.  Its popularity peaked in the mid-1800’s when the French discovered that essential oils from the rose geranium could be substituted for attar of roses in perfume making.  Entrepreneurs soon cashed in on the use of this much cheaper and more readily available ingredient.  Even today, the scented geranium has a place in the perfume industry, mainly in the manufacture of men’s cologne. 

Scented geraniums were brought to our country by early colonists.  It is reported that Thomas Jefferson was especially fond of the species and even planted several varieties at the White house.  Many Victorian gardeners and collectors also grew them and made good use of the scented leaves in bouquets and potpourris, as well as in recipes for cakes, cookies and jams. 

In 2006, the scented geranium was dubbed Herb of the Year by the International Herb Association, selected on account of its foliage, color, form and scent, but unfortunately, not its flowers.  Sure, they are small by comparison, and certainly not as bold as those of their Memorial Day cousins, but the fact that they bloom in early spring makes them all the more appealing, kind of an added bonus to an already wonderful plant.

To have success growing scented geraniums indoors, plant them in a well-drained potting mix and situate in bright light.  Fertilize monthly in spring and summer and, as already mentioned, every other month during the fall and winter.  To produce a giant specimen, plant your geranium in the ground for the summer months; it will relish the heat and respond by growing in leaps and bounds.