"And the seasons, they go round and round..." (Joni Mitchell - The Circle Game)
As we now rapidly approach the autumnal equinox and with it the "official" astronomical season of autumn (tonight about 10:30 PM EST), I thought I'd offer a few thoughts on fall gardening.
Autumn is the premier time for gardening in South Carolina! Indeed, the period of time we casually refer to as "fall" really consists of the end of summer, autumn proper, and the beginning of winter. Fall is a diverse season, and one of a particular somewhat melancholy beauty.
"Fall" of course - as in the season - is the result of the tilt of the rotational axis of the earth and what that tilt means as the earth makes its way each year around the sun.
OK, so I just typed the phrase "rotational axis," a phrase which may or not make any sense to you.
Imagine standing in your living room and slowly spinning around. You are upright and your body is perpendicular to the floor. There is a straight line which runs through the center of your head down through your body to the floor. You are spinning, as it were around this line. This line is called the axis of rotation, the line around which you are rotating.
Now imagine (and in the case you have to imagine it because it would be about impossible to do it) tilting your body just a few inches to the side as you spin. Now there is still that line running through your head to your feet and you are still spinning around it, but now that line, that axis of rotation, is not perpendicular to the floor. We would say that the axis of rotation is tilted relative to the floor.
Imagine however a round object spinning, say a basketball. Now imagine that there is a metal rod running from the top of the ball through the bottom (I know in real life this would deflate the ball but just imagine). So you are spinning the ball around the rod, and the rod is straight up and down. But say now you tilt the rod to one side and keep spinning the ball. The ball is a sphere and spheres themselves don't tilt. But the line around which the ball is spinning is titled. It's axis of rotation relative say to the ground is tilted.
Hold that thought...
There are several things which impact local temperature and weather. One of the most significant things is the angle at which the light from the sun strikes the earth's surface. Say you have a flashlight and you are shining it straight down onto the floor. Say this is a really odd square flashlight which lightens up a perfect square on the floor. Now imagine shining this square flashlight at the floor at an angle. The area on the floor which is lightened is no longer a perfect square but a rectangle. The area of this rectangle when the light does not shine from straight overhead is greater than the area of the square when it does. Thus the very same amount of light and light energy is spread over a larger area, which means that the light is slightly less intense at any one spot.
Imagine doing a similar thing except this time you are shining a light horizontally onto a piece of paper. Again, if the paper is perpendicular to the source of the light you would get a perfect square of light on the paper. But tilt the paper backwards away from the light and that square becomes a rectangle, and the farther you tilt the paper the bigger the rectangle gets, and the less intense is the light on any one point of the paper.
This tilt or paper in our imaginary experiment is sort of like the round earth curving back and away from the light of the sun. As one goes from equator to poles the sunlight is less and less intense because the same amount of light is spread over a progressively larger area. By the time you get to the "top" of the earth the light is actually perpendicular to the surface and not hitting it at all.
When it comes to the earth there is another even more significant reason the light is less intense the further away from the equator you go, and that is the atmosphere. As the sun strikes the part of the earth curving away (as it were) from the light it must travel through more and more atmosphere before it hits the surface. The atmosphere is filled with bits of particulate matter like dust and gaseous molecules which impede the flow of the light.
These two factors - the curve of the earth away from the light plus the increasing interference of the atmosphere, means that light intensity towards the top and bottom of the sphere is much diminished, and thus it is much colder.
Again, if our earth rotated on an axis perpendicular to the path it travels around the sun, weather and temperature would be pretty uniform at any one place as the intensity of light from the sun would be more or less the same all year round. No seasons. No fall colors. No springtime burst of life. No articles about fall or spring gardening.
But the rotational "tilt" of the earth changes things. It has added greatly to the complexity and the diversity of life on earth. It is hard to imagine our earth without it.
Now if you are having a hard time picturing this "tilt" as the earth goes around the sun look at the simple video here This little video shows something very important that you should notice carefully. The tilt of the earth as the earth travels around the sun always faces the same direction.
Imagine holding a small pencil in one hand and tennis ball (or any object) in the other. This pencil is titled, it's point facing, say, the same wall of your room. Move the pencil in circles around the tennis ball but always have the top of the pencil face the same wall of the room. Notice that at one point the tip of the pencil is facing the ball, and then on the other side of the circle it is facing away from the ball. Half way between these two points it is neither facing toward or away from the ball. This happens twice each trip around the ball. These moments correspond to our spring and fall equinoxes.
If you can look again at the little video linked to above you will notice something else important. When the northern hemisphere is tilted toward the son the light of the sun is shining directly not on the equator but a point above the equator (the Tropic of Cancer), and when the northern hemisphere is tilted away from the sun the sunlight is hitting directly on a point below the equator (the Tropic of Capricorn). Only halfway between these two points is the sun shining directly above the equator. And only only on these two dates does the sun rise and set all over the earth exactly due east and due west respectively. And only on these two days are "daylight" and "nighttime" of the same duration.
If you want to get a feel for due west, head down to the State House later today and watch the sun set. It will be setting due west.
OK, back to the tilt....Because of this steady tilt of the rotational axis, our northern hemisphere leans as it were closer to the sun in the summer and further away from the sun in the winter. Interestingly the earth is slightly closer to the sun in our northern hemisphere winter.
(Of course the tilt does actually move over time, about every 26,000 years, which would slowly change (if our calendar stayed the same) what months of the ear it is winter and summer and so forth, but we won't go into earth's wobble here)
Because of the tilt, when the northern hemisphere is tilting away from the sun, it gets cold, even very very cold. And it is this period of cold we call winter that has for millions of years been a barrier to continued plant life, and only those plants that have developed some mechanism for ongoing survival through winter have, well, survived, and are still with us.
The plants and trees around us offer a mind boggling diversity of how they have adapted to these varying seasonal conditions, and especially to winter. How will plants survive from one year to the next with that big survival problem we called winter waiting to exterminate them?
As we now rapidly approach the autumnal equinox and with it the "official" astronomical season of autumn (tonight about 10:30 PM EST), I thought I'd offer a few thoughts on fall gardening.
Autumn is the premier time for gardening in South Carolina! Indeed, the period of time we casually refer to as "fall" really consists of the end of summer, autumn proper, and the beginning of winter. Fall is a diverse season, and one of a particular somewhat melancholy beauty.
"Fall" of course - as in the season - is the result of the tilt of the rotational axis of the earth and what that tilt means as the earth makes its way each year around the sun.
OK, so I just typed the phrase "rotational axis," a phrase which may or not make any sense to you.
Imagine standing in your living room and slowly spinning around. You are upright and your body is perpendicular to the floor. There is a straight line which runs through the center of your head down through your body to the floor. You are spinning, as it were around this line. This line is called the axis of rotation, the line around which you are rotating.
Now imagine (and in the case you have to imagine it because it would be about impossible to do it) tilting your body just a few inches to the side as you spin. Now there is still that line running through your head to your feet and you are still spinning around it, but now that line, that axis of rotation, is not perpendicular to the floor. We would say that the axis of rotation is tilted relative to the floor.
Imagine however a round object spinning, say a basketball. Now imagine that there is a metal rod running from the top of the ball through the bottom (I know in real life this would deflate the ball but just imagine). So you are spinning the ball around the rod, and the rod is straight up and down. But say now you tilt the rod to one side and keep spinning the ball. The ball is a sphere and spheres themselves don't tilt. But the line around which the ball is spinning is titled. It's axis of rotation relative say to the ground is tilted.
Hold that thought...
There are several things which impact local temperature and weather. One of the most significant things is the angle at which the light from the sun strikes the earth's surface. Say you have a flashlight and you are shining it straight down onto the floor. Say this is a really odd square flashlight which lightens up a perfect square on the floor. Now imagine shining this square flashlight at the floor at an angle. The area on the floor which is lightened is no longer a perfect square but a rectangle. The area of this rectangle when the light does not shine from straight overhead is greater than the area of the square when it does. Thus the very same amount of light and light energy is spread over a larger area, which means that the light is slightly less intense at any one spot.
Imagine doing a similar thing except this time you are shining a light horizontally onto a piece of paper. Again, if the paper is perpendicular to the source of the light you would get a perfect square of light on the paper. But tilt the paper backwards away from the light and that square becomes a rectangle, and the farther you tilt the paper the bigger the rectangle gets, and the less intense is the light on any one point of the paper.
This tilt or paper in our imaginary experiment is sort of like the round earth curving back and away from the light of the sun. As one goes from equator to poles the sunlight is less and less intense because the same amount of light is spread over a progressively larger area. By the time you get to the "top" of the earth the light is actually perpendicular to the surface and not hitting it at all.
When it comes to the earth there is another even more significant reason the light is less intense the further away from the equator you go, and that is the atmosphere. As the sun strikes the part of the earth curving away (as it were) from the light it must travel through more and more atmosphere before it hits the surface. The atmosphere is filled with bits of particulate matter like dust and gaseous molecules which impede the flow of the light.
These two factors - the curve of the earth away from the light plus the increasing interference of the atmosphere, means that light intensity towards the top and bottom of the sphere is much diminished, and thus it is much colder.
Again, if our earth rotated on an axis perpendicular to the path it travels around the sun, weather and temperature would be pretty uniform at any one place as the intensity of light from the sun would be more or less the same all year round. No seasons. No fall colors. No springtime burst of life. No articles about fall or spring gardening.
But the rotational "tilt" of the earth changes things. It has added greatly to the complexity and the diversity of life on earth. It is hard to imagine our earth without it.
Now if you are having a hard time picturing this "tilt" as the earth goes around the sun look at the simple video here This little video shows something very important that you should notice carefully. The tilt of the earth as the earth travels around the sun always faces the same direction.
Imagine holding a small pencil in one hand and tennis ball (or any object) in the other. This pencil is titled, it's point facing, say, the same wall of your room. Move the pencil in circles around the tennis ball but always have the top of the pencil face the same wall of the room. Notice that at one point the tip of the pencil is facing the ball, and then on the other side of the circle it is facing away from the ball. Half way between these two points it is neither facing toward or away from the ball. This happens twice each trip around the ball. These moments correspond to our spring and fall equinoxes.
If you can look again at the little video linked to above you will notice something else important. When the northern hemisphere is tilted toward the son the light of the sun is shining directly not on the equator but a point above the equator (the Tropic of Cancer), and when the northern hemisphere is tilted away from the sun the sunlight is hitting directly on a point below the equator (the Tropic of Capricorn). Only halfway between these two points is the sun shining directly above the equator. And only only on these two dates does the sun rise and set all over the earth exactly due east and due west respectively. And only on these two days are "daylight" and "nighttime" of the same duration.
If you want to get a feel for due west, head down to the State House later today and watch the sun set. It will be setting due west.
OK, back to the tilt....Because of this steady tilt of the rotational axis, our northern hemisphere leans as it were closer to the sun in the summer and further away from the sun in the winter. Interestingly the earth is slightly closer to the sun in our northern hemisphere winter.
(Of course the tilt does actually move over time, about every 26,000 years, which would slowly change (if our calendar stayed the same) what months of the ear it is winter and summer and so forth, but we won't go into earth's wobble here)
Because of the tilt, when the northern hemisphere is tilting away from the sun, it gets cold, even very very cold. And it is this period of cold we call winter that has for millions of years been a barrier to continued plant life, and only those plants that have developed some mechanism for ongoing survival through winter have, well, survived, and are still with us.
The plants and trees around us offer a mind boggling diversity of how they have adapted to these varying seasonal conditions, and especially to winter. How will plants survive from one year to the next with that big survival problem we called winter waiting to exterminate them?
There is a large northern red oak right outside my front door. Strewn all around are bits and pieces of acorns partially eaten by squirrels. Soon there will be thousands of these acorns, more than the squirrels can keep up with. In addition, looking closely, one can detect changes in the leaves as at least some have already begun the process of organized death, breaking down complex molecules in the leaves into soluble forms and transferring these smaller but rich compounds back to the tree proper for storage in stems and trunk and and roots.
Thanks to squirrels with which oaks have co-adapted, oak seeds will be spread well beyond the drop zone as the cute rodents "squirrel" away food for winter, and then, thankfully forget where they put them. In this way young oak trees can sprout and in time replace the parent oak which will, in it's own time, crash to the ground. Meantime however, that very same parent oak is securing its own healthy survival of winter by storing away nutrients for a burst of growth and life next spring when there will be no production of new food via photosynthesis, since of course there will be no leaves. This food energy is being stored in leaf and flower buds as well as in stems and roots. The food stored in buds will provide for that immediate burst of growth in early spring, and the food stored in other parts of the tree will feed the new leaves until they become net producers of food themselves.
Different sort of plants have different ways of surviving winter. Many plants send a great deal of energy to tubers, bulbs, and rhizomes for example. Many other perennials whose above ground leaves and stems die back completely, grow deep roots and transfer water from root cells to the surrounding soil to protect their cells from rupture during cycles of freeze and thaw.
Evergreens offer a complicated alternative, complicated in terms of understanding the adaptive advantages and disadvantages. Most temperate climate evergreens originate in areas of poor soil where, in the spring, they must be able to produce their own food quickly through photosynthesis. It takes a huge amount of energy for deciduous plants to be able to support flower and leaf growth in the spring without active food production, which requires rich soil and massive food reserves. But even most evergreens become dormant or mostly dormant in the winter, growing and photosynthesizing hardly at all.
So what does all this mean for fall gardening? Let's look at what the fall season means for a few major categories of gardening.
Composting/Mulching
Since I have been talking about autumn leaf-fall, I would be remiss if I didn't mention one of the most important things you can do in the fall, and that is rescue those precious leaves from the landfill! Every year we send away tons and tons of nature's very own compost, and then spend money to replace it with inferior material! It makes no sense whatsoever.
Even though plants in fall do transfer important nutrients from leaves back to the stems and roots to use the next year, much is left in the leaf that can be turned by soil microbes into a wonderful medium for plant growth. This process also builds a rich and diverse soil ecosystem.. The microbes and other invertebrate animals that make a living on decomposing leaf litter themselves become food for insects which become food for birds. Leaves also provide organic material for our sandy soils which allows the soil to hold on to more water and nutrients.
Leaves do not have to worked into the soil - they can be spread as mulch and over time worms and other critters will incorporate them into the soil.
As you know leaves that are simply thrown into a pile and forgotten will create mats which take a long time to decompose. The trick to maximizing the potential of leaves in the garden is shredding!
One of the easiest ways to shred leaves is to spread them out a few inches deep and go over them a few times with the lawn mower. You can also purchase a gas or electric leaf shredder locally or online. The electric shredders are much less expensive and a little more tedious to operate, but well worth the money and effort. I used one for years in Greensboro and transformed our red clay soil into a thing of beauty. But again, using the lawn mower also works.
Spread these shredded leaves around your plants or place them in a compost bin and let the magic begin!
Planting
Fall as you know is the very best time to plant in our climate. True, planting can be done any time of year here, even in the hottest part of summer or coldest part of winter, but fall is ideal. Why? Well, the biggest challenge for any newly planted plant is water. As temperatures decline and transpiration decreases, water demand decreases. As I like to say, we can plant any time of year as long as we water, but the potential consequence of forgetting to water is quick and massive in the summer, and less so in the fall.
The ideal time to plant is while it is still warm enough for reasonable growth (particularly the growth of new roots and root hairs which will serve the plant through the winter), but not so hot as to stress the plant necessarily. If planted earlier in the fall when it is still quite hot just be sure to water regularly. If planted late in the fall when temperatures are quite cold - that's OK too, since the temperature just a little but below ground level is quite higher than air temperature and warm enough for slow root growth - just add some extra mulch for insulation and don't forget to water just because it is almost winter. Roots grow in winter too.
Fall is a great time for planting or dividing corms/bulbs/rhizomes/tubers - you know those plants with big storage systems underground that we collectively call "bulbs." Would you like a cheerful splash of yellow in your garden early next spring? Daffodils will do the job. The are available from a lot of different mail order catalogs (contact me and I will pass along some suggestions). They are best planted in clumps, not isolated here or there. Daffodils, crocuses, hyacinths, snowflakes, and true liles can all be planted from September to November for spring bloom. Day lilies should be planted sooner rather than later. Now is a great time to dig and divide crowded clumps of day lilies for planting around the garden. It is also a good time to divide and plant many irises.
Speaking of digging and dividing and replanting, now is the perfect time to divide crowded beds of black eyed susan, daisies, phlox, cast iron plant, liriope, pretty much any perennial that likes to spread its wings each year and thus get more and more crowded. The more crowded thse plants become the fewer blooms, so dividing is really helpful!
Pruning
Winter creates an interesting challenge when it comes to pruning. There are basically two questions. First, how long after pruning is it likely to be before there is a hard freeze? .Pruning almost always stimulates new growth, growth which tends at first to consist of soft herbaceous tissue. If there is a hard freeze before this soft new growth can harden up it can be killed back by the cold, producing a dead stub. This is both unsightly and an unnecessary opening to the plant of disease. Sometimes it is just better to wait a bit until winter dormancy has set in. Second, does the plant bloom in early spring? If it does it is probable that the plant has already invested energy in producing flower buds with winter resistant scales. Obviously if one cuts away these buds in the process of pruning there will be few blooms the following spring, and the plant will have wasted its energy investment in buds. On the other hand, one does not want to look at wayward stems or spires all winter, so careful selective pruning of these wayward stems will not ruin the display of color in the spring.
For an excellent guide to pruning provided by Clemson Extension, click here.