Monthly Archives: November 2012

Forcing Hyacinth Bulbs

While winter is still a month away, a part of me is thinking of spring. This is the time of the year when I pot up hyacinth bulbs in order to have them bloom in February and March.

You can force almost any spring bulb but I’ve found that hyacinths are the most reliable. They’re easy to plant and when you bring them into the house in late winter, they don’t seem to be as affected by the conditions of a closed, heated house as other bulbs. Plus it’s so nice to have that hyacinth smell fill a room while it’s snowing outside.

Hyacinths Almost Touching in a Pot – the next step is covering them with soil

To force hyacinths you simple plant the bulbs in a container with potting mix. The bulbs can almost touch each other in the pot and the soil only needs to come up to the tips of the bulbs. I find that three bulbs work well in a 6″ pot. After watering the soil, there is one trick that I’ve learned. Hyacinths have very strong roots. When they’re grown in a pot, the roots will often push the bulb right out of the soil when they begin to grow. To prevent this, I stack the pots 2 or 3 high and then put an empty clay pot on the top of the stack. I leave the pots this way for a few weeks. This allows the roots to grow into the soil and prevents the bulbs from being pushed out the soil.

To force hyacinths, they need a period of cold like they’d receive if they were planted in the garden. You can put the pots outside in a cold frame, bury them in the ground or cover them with leaves or straw. But I’ve found that a styrofoam cooler kept in an unheated garage works great. The pots stay cleaner, no insects get into the soil and the insulation seems to be enough to keep the bulbs from getting too cold. Once the bulbs have rooted, I put them in a cooler and leave them there for 8-10 weeks. During this time I occasionally check them to make sure that the soil is moist, but that’s it.

Forced Hyacinths

You can start bringing in the bulbs after this cold treatment when there’s a 1/2″ to 1″ shoot growing from the bulbs. I don’t do anything special with the pots – I just bring them into the house and keep them in the sunniest location I can find. In about a month the hyacinths will be blossoming. For a steady supply of flowers you can bring in a pot ever week or so and you’ll have hyacinths until the start of spring.

After the flowers have died, I keep the pots well watered and when the hyacinths are growing in the garden, I plant the pots of forced hyacinths into the garden as well. They usually come back and blossom the next year.

(A note – if I were really driven I could have these bulbs blooming for Christmas or New Year’s. I’d have to plant them in late August and keep the pots in a refrigerator to provide an artificial cold treatment. While it can be done, it’s too much work for me – February bloom time is soon enough for me.)

Planting hyacinths in November is one of those things that I have to remind myself to do – it’s easily forgotten amidst all the chores of fall clean-up. But in February, I’m always glad that I did it.


Fall Colors: Part III – Leaf Fall

Trees Post Sandy

Two weeks ago Hurricane Sandy passed directly over this part of PA. While we didn’t suffer the devastation of the Jersey shore, we did have rain and wind. But even with all of the wind, the leaves stayed on a majority of the trees. That got me thinking about how leaves fall from a tree. I was reminded of one of the few things I remember from plant anatomy class and it all has to do with some special cells that connect the leaf to the twig.

As a tree gets ready for winter, it has to somehow deal with its leaves. If the leaves were to stay on the tree, there would be a lot of damage in the winter due to the weight of snow building up on the branches and leaves. Just think of the damage that occurs when we have an early snowfall before the leaves are gone. Somehow the tree needs to lose its leaves before the winter weather.

But the tree also has to accomplish this leaf loss in such a way that there isn’t a lot of exposed tissue. If leaves were just pulled off of a tree, the places were the leaves were connected to the twig would be an open wound. This would be an avenue that would allow bacteria and fungi to enter the tree. So the tree needs to not only lose its leaves but also do it in a way that protects it from pathogens.

Deciduous trees and bushes have evolved a way to lose their leaves in the fall (abscission) while doing so without creating open wounds. It all has to do with the abscission zone.

In the area where the petiole of the leaf (the small “stem” of the leaf) joins the twig, there’s an abscission zone made up of two kinds of tissue – the abscission layer and the protective layer. The protective layer is closest to the twig; the abscission layer is between the protective layer and the petiole. Both of these layers are only a few cells thick. During the growing season this layer of cells is healthy and keeps the leaves attached to the tree. But when the days become shorter, things begin to change in this zone.

The protective layer begins a process called suberization in which suberin, a waxy chemical found in cork, builds up in the cells. This provides an area of tissue that’s impervious to the outside elements. The suberized protective layer prevents leaf fall from leaving open wounds on the twigs.

While the protective layer is becoming filled with corky tissue, the abscission layer also transforms. Chemical changes in the tree cause this layer of cells to break down. When the cell walls have broken down sufficiently, the leaf will fall and the protective layer will show on the twig as a leaf scar.

It could be said that the leaves on a tree don’t fall so much as they are released by the tree. The tree breaks down the abscission layer and when it does, the leaves are sloughed off. Each kind of tree releases its leaves on its own schedule. In my yard the asian pear and redbud lose their leaves in early October while the maple and willow are just beginning to lose their leaves in mid November. When the abscission layer breaks down is species dependent but it eventually breaks down in all deciduous trees.

Sandy blew through the neighborhood but she couldn’t remove the leaves from the trees because they weren’t ready to be shed. But now the leaves are starting to fall in earnest. The protective layers have suberized and the abscission layers have broken down. The trees have done their part to prepare for winter. Now it’s time for me to do my part – rake the leaves!

Fall Colors: Part II – Red, Crimson and Purple

There are years when the colors of the autumn leaves are stunning and there are other years when the display is a little muted. A lot of this difference has to do with the red, crimson and purple colors of fall.

While the yellow colors (carotenoids) of fall are generally consistent from year to year, the same isn’t true for the various shades of red. The pigments that cause these colors in the leaves are anthocyanins, the same pigments that give color to cranberries, apples, cherries and grapes. While carotenoids are present in the cells of the leaves all year-long, anthocyanins usually are not. Also not all trees produce anthocyanins – for example, you won’t see red leaves on an aspen. Trees that do produce this pigment, like maple trees, do so in the fall.

In order to have a bright red display of leaves, the conditions need to be just right. The best reds are produced when the days are warm and sunny and the nights are cool but not freezing. During a warm, sunny day in the fall, the remaining chlorophyll in the leaves is able to photosynthesis and produce a lot of sugar. This it the same process that goes on throughout the growing season.

But when the days become shorter, the vascular tissue of the leaves begin to shut down. The sugars that easily moved from the leaves to the tree during the summer now become trapped in the leaves. Cool nights mean that there’s little breakdown of the sugar. The result is that the leaves become saturated with sugars.

When there’s lots of sugar in the leaves and the days are sunny, the tree leaves convert the sugars into anthocyanins. These pigments are water-soluble and are stored in organelles within the leaves called vacuoles. Vacuoles are membrane enclosed structures used for storage of water and other materials. When the days of fall are sunny and warm and the nights are cool, these vacuoles become filled with anthocyanins. Later in the fall when the chlorophyll of the leaves finally breaks down, the anthocyanins can be seen and the leaves appear red, crimson and/or purple.

Since these pigments are found in the water-filled vacuoles of the leaves, the amount of moisture in the soil can also affect the fall display. If there’s a lot of water in the leaves, the anthocyanins can end up being diluted and the resulting colors will be less intense.

With all of the varying factors of light, temperature and soil moisture, no two autumn displays of color will be the same. Some years the red pigments will be intense; other years they’ll be absent. It all depends on the leaves’ ability to produce anthocyanins and the amount of these pigments that are stored in the leaves.

It’s exciting to know that each year will be different and the combinations of these environmental factors will lead to different shades of red, crimson and purple. Add to this the fairly consistent yellows and each autumn display is unique. Someone should take pictures of the fall colors from the same location on the same day for a number of years. It would be fascinating to see the differences in the display from year to year. While they’d all be different, they’d also all be beautiful in their own way.