Apple of the Earth

Potato (Solanum tuberosum) 'Yukon Gold' 

Once again the earth has given forth its fruits through the humble night shade the French appropriately call -- Pomme de terre! 

Last winter I planted some sprouted potatoes from my pantry and under minimal input and less than six hours of sunlight (due to its location), here they are, food once more and even more.  Since I planted them from leftover tubers, I didn't do as much management as I would have. However, there are some things that can be done to optimize potato harvests.  For the sake of those who are interested in trying potatoes in the future, here is a list of activities worth considering:

1.  Hill-up the soil during early growth of the stems.  Stolons (the part that becomes tuber) grow on buried parts of the stem.  Covering more of the basal stem allows the formation of more tubers.  Since my potatoes were grown in large pots, I could have simulated hilling-up by adding more soil at the base of the plants;

2.  Water when necessary.  Use rainfall instead of the temperature as basis for watering.  The low temperatures of winter is often deceiving.  I tend to assume the soil is moist when the air temperature is cold.  My mistake.  After tuber initiation, consistent water supply (along with other factors such as sunlight and fertilizer) is very important for a good bulking rate (enlargement) of the tubers;

3.   Apply a second dose of fertilizer.  Fertilizer was basally applied but I skipped the necessary side-dressing which would have enhanced and prolonged foliage growth that results in large potatoes.  

Below the Soil Surface

Fig. 1  Volunteer potato plant.

Ever since I planted my first potato crop in my garden, volunteer potato plants became a normal occurrence every spring.  No matter how much I'd try to look for all the tubers at harvest time, there would always be some tubers left behind.   As a general rule, I rarely use the same area in my garden for the same crop two seasons in a row.  In other words, I practice crop rotation.  The result of this is that some of the weeds that I have to remove from my garden before planting my spring crops are volunteer-potatoes (Fig. 1).   Sometimes when I pull them out of the ground they already have new potatoes (small and immature tubers) which when boiled and buttered make a treat for my kids.

When I was pulling the volunteer potatoes, I saw one that I could use as a visual aid for something I'd like to talk about - the parts of a potato plant that directly affects its performance.

 

 Parts of a Potato Plant: Underground (Part One)

Fig. 2 Parts of a growing potato plant.

Mother tuber is the seed tuber that was planted and where the new crop has grown from.  My former professor, Peter Vander Zaag, used to say that when a healthy seed tuber is planted, it is likely that it will remain till harvest time as a mother tuber.   Why it is called a mother tuber-- I'm guessing that it is because it has had the chance to reproduce.  :)  A firm and healthy mother tuber at harvest time indicates that the early growing conditions of the crop was  favorable allowing the new plant to shift from being dependent (drawing energy from the mother plant), to independently producing energy (through photosynthesis) before the energy from the mother tuber is depleted.

The mother tuber in the picture (Fig. 2), being a volunteer potato, was situated close to the surface of the soil.  It was exposed to a larger array of pests as indicated by the presence of holes on  the tuber. 

Fig. 3.    Stolons develop underground; lateral stems develop above ground. 

Fig. 4.   Sprouts on the seed tuber corresonds to the stems of the potato plant.

Main stems of potatoes grown from tubers are those that directly grow from the mother tuber. The sprouts (Fig. 4) on the seed tubers eventually grow into stems (Fig. 3). Stems that grow from the main stems are called lateral stems. The stem grows above ground but it has an underground section which is consist of the stolon, tuber, and roots. The length of this section of the stem is a function of planting depth and hilling-up. The greater the distance between the mother tuber and the top of the soil the more internodes will there be

The stems are generally green but the buried section is white (Fig. 2 and Fig. 3). Depending on species the stems could also be purple or reddish brown. 

Stolons are underground lateral stems (branches). They are easily identified as being thick white long structures arising from the nodes that are covered with soil (Fig. 5). Under favorable conditions, the apical end of the stolon eventually swells and develops into a storage organ called tuber. This stage is technically known as tuber initiation (Fig. 5). When the apical end of the stolon is exposed to light, it starts to produce chlorophyll and functions as a normal lateral stem or branch (Fig. 3).  One stolon potentially produces one tuber - hence the number of stolons in one plant determines the number of tubers produced.  

Fig.  5   Tuber initiation - apical ends of stolons developing into tubers.

Nodes are the points on the stem where buds, lateral branches, and  leaves originate.  In the case of the underground part of the potato, it is the point where the roots and stolons arise.   The space between nodes on the stem is called internode.  Planting deep enough to allow more nodes below the soil surface helps increase root and stolon formation.

Roots.   Potatoes that are grown asexually (from tubers) develop adventitious roots.  The potato plant has a root system that seem unsubstantial (Fig. 2) and growing superficially during its early growth stage [1].   Maintenance and conservation of soil moisture is important for this crop.   For small gardens, mulching is a practical management practice to take into consideration.    

Understanding the growth habits of plants help gardeners choose appropriate management practices for their crops.

Fingerling Potatoes



Fig. 1   Fingerling Potatoes (Solanum tuberosum)

Fingerling Potatoes are small, narrow, and elongated potato tubers in their mature stage.  Some varieties resemble the shape of fingers (Fig. 1), hence the term fingerling.  Other varieties have distorted shapes because of deep eyes (Fig. 3) but they still count as fingerling because they meet the size.  Fingerling potatoes range from one to two inches in diameter and with lengths ranging from two to three inches.  



Fig. 2   Assorted varieties of fingerling potatoes in various colors

Posh price for posh potatoes.  Fingerling potatoes have now become popular in upscale grocery stores.   They are turning up on the featured entrées on menus of fine restaurants in big cities.   The novelty of their petite size, unusual colors (including deep purple) and texture provide extra drama on the otherwise traditional potato.  Its posh position in the modern culinary world is reflected on its price tag.  Try going to the stores and compare the price against the other potato varieties and you will come up with a price that is three to five times more expensive.



Fig. 3   Etiolated sprouts grown in the dark.

From my pantry to my garden.    From time to time we would buy a bag of fingerling potatoes from Costco - but this time the tubers started to sprout before we could eat them all.   They were stored in a dark corner of my pantry hence the etiolated white sprouts (Fig. 2 and Fig. 3).  Etiolated sprouts are not fit for planting because of their lack of vigor.  So I placed them in a tray by the window sill to expose the tubers to diffused-light.  After ten days the sprouts looked more sturdy and vigorous  producing the necessary pigmentation (Fig. 4).   Now, that is the appearance of a seed tuber that promises a good crop (Fig. 4).

Fig. 4   Green and vigorous sprouts - qualities of a good seed tuber.

Sometimes the pantry can be a source of planting materials. 

Some Things About Potatoes

Harvesting volunteer potatoes.

Volunteer plants are those that grow in the garden even in the absence of intentional care.  Volunteers arise from plants whose seeds and vegetative parts (such as rhizomes, tubers, roots and stems) survive under neglect.  This is natures' way of maintaining vegetation on this planet.  But when gardeners were born and their designs were printed, some of these volunteers have been labeled as weeds. 

In my garden potatoes would grow voluntarily every year even if I only planted once.   These are the potatoes that skipped my trowel during the previous harvest.   Early in the spring they would sprout right where they were left.   After three to four months when the leaves begin to turn yellow, we are ready to unearth the goodness that lies underneath the soil.   Today I will use these volunteer potatoes to share some useful lessons in gardening that I learned over the years.  Did I mention that I once was a potato scientist working with the International Potato Center in my younger days?  

Potato (Solanum tuberosum):  Tubers were very close to the soil surface.

A tuber hangs among many roots.

Tuber.  The part of the potato that we eat is called a tuber. It is a modified stem...not a root.    That's right the potato is technically a stem.   Tubers grow from a stolon which is a stem that grows underground.   This can be easily distinguished from the roots by their size and color.  Stolons are white and are much thicker than the roots. 

Tuber - "Bigger than my hand!"

Eyes.  The indentations on the potato tubers are called eyes.  Although they cannot see, believe me these eyes have brows. :)  Observe them the next time you peel some potatoes.   The eyes are the nodes of the modified stem.  On a regular stem, this is where branches would come out.  That is why when you keep your potatoes in your pantry for a long time, sprouts would come out.  If you plant those sprouting potatoes, those sprouts become the plants.  Did you know that potato varieties with deeper eyes are less desirable than their shallow-eyed counterparts?

Tubers harvested from one potato plant.

Greening.  Notice that the potatoes although harvested from the same plant did not have the same colors.  Some of them are green.  Greening in potatoes is the development of chlorophyll on the tubers caused by the exposure of the tubers to light.  The absence of hilling-up (raising the soil around the base of the plant) on these potatoes resulted in tubers that grow very close to the soil surface and thus exposure to sunlight. 

To prevent greening - always store your food potatoes in a dark place or cover them with a towel.  I don't recommend eating potatoes that show signs of greening for these reasons:  they don't taste good; they don't cook easily; and most of all they contain some amounts of toxic substances (glycoalkaloids).  

                              

Ugly potatoes with enlarged lenticels

Lenticels.  These are small openings on plant tissues that allow gas exchange.  In other words, they likened to the nostrils.  The bumps seen in the picture above are not diseases; they lenticels that have been enlarged.  The volunteer potato that we harvested was growing next to a leak in the drip line which created an anaerobic (absence of air) condition within the soil.  The lenticels had to open, as flared nostrils, in search of oxygen.  This is what happens when plants are over-watered - the lenticels swell and they can be a convenient entrance for microorganisms. 

I have to stop here but expect for more posts on potato-related topics in the future.