Planning Your Planting Calendar: How to Figure Out What to Plant & When

Planning your planting calendar requires first knowing the number of days required before harvesting each crop. The number of day to maturity of each plant varies depending on the specie.

Let's tale the example of Amish Peas for instance.  This particular variety will be ready to eat in 60-70 days from the time of its transplanting outdoors. The British Wonder variety takes only 50-55 days. The "days to harvest" is one crucial piece of information you can use from the seed packet.

A little Disclaimer: Plants have evolved in specific environments. They have adapted to flourish in those environments by tuning their senses to the weather, the sunlight, the moisture.

So as you read through this article, please note that while there is a human tendency to view (and present) plants as simple organisms with specific rules, sometimes, our crops just don't follow the rules.  In continuing to learn more about cellular biochemical mechanisms, it's apparent that plant dynamics are far more sophisticated even at the cellular level than any planting calendars we've constructed ourselves.

The photo above is from a study that shows how plants adapted to the new locations they were moved to. 

This constant miraculous reminder of nature's sophistication gives us a greater appreciation of life in general. You start to link gardening to something deeper beyond the immediate need to feed the body (although that's important too!)

There are a few environmental triggers that kickstart a plant into growth.

• Germination Temperatures
• Day-Length
• Other factors such as snow/cold (also known as stratification), scarification, moisture, sound, etc., will not be discussed in detail here. 

Since plants have tuned themselves for specific triggers and sensory events, they will grow at a much faster speed when they've determined that it is their optimal time to grow. Taking advantage of that knowledge will help us maximize the growth curve of the plant. 

We grow certain crops for their leaves, stems, or bulbs. These are plants we do not want to flower or "bolt." (Think of having eaten bitter lettuce that has flowered and gone to seed.)

Other crops we grow specifically for their flowers because their flowers and subsequent fruits are the parts we eat. (Think tomatoes, squash, peas, cauliflower, cabbage, broccoli.)  

Peas for instance, are plants that would first need to experience 12 daylight hours before they form the pea pods we love to eat. 

This physiological reaction is known as photoperiodism.  Plants that are sensitive to daylength fall into three categories:

• Long-day - plants that flower, when the days lengthen or nights, shorten
• Day-neutral - plants that are not affected by day or night length
• Short-day - plants that flower when the night lengthens

Here's a brief intro to photoperiodism from Khan Academy

Long-day varieties look for at least 12 hours of sunlight to bloom. These plants are often:

• Barley
• Beets
• Bulbs such as alliums (onions, garlic)
• Carrots
• Lentil
• Lettuce
• Oats
• Parsley
• Potatoes 
• Peas
• Radish
• Rye
• Spinach
• Swiss Chard
• Turnips
• Wheat 

Short-day varieties look for less than 12 hours of sunlight. These plants are often

• Fava Beans
• Green Perilla
• Kale
• Lima Beans
• Maize/Corn (some varieties)
• Rice
• Sorghum
• Soybeans
• Sweet Potato
• Strawberries
• Sugar Cane
• Squash

Day-neutral plants don't care either way, whether the nights are long or the days are short.

• Cucumber
• Corn (some varieties)
• Tomatoes
• Peas

Plants, however, are adaptable.  Studies such as these have found that some previously long-day varieties changed their photoperiods as crops migrated to higher or lower latitudes. They bloomed where they were planted. 

Armed with a little more information about the amount of light the plant wants, we can go back to our optimal days of growth and tweak the starting/ending date based on the day length.

Determine your location's latitude (for instance, In Northern VA, 39 degrees N), then take your start and end dates for your target plant and look up the amount of hours that your latitude receives sunlight using these great latitude daylength charts or MrReid.org, a physicist and a teacher's website.

When you include photoperiod in your calculations, remember to ask yourself first, "Do I want this plant to flower or not?" If you answer, "No," you will most likely need to adjust your growing calculations.

Fortunately, you can find germination temperatures for many common crops by Googling "Germination temp of [insert crop here]."

Let's take the example of a fast-growing crop like Corvair Spinach. The spinach seeds when direct sown outdoors, will germinate best when the temperature range is between 45-75F (7-24C).

You can find your location's average temperatures by day/month in the US on websites like weather.com.   If you Google "Monthly average temperatures [insert your zipcode here],"  and click on "graphs," you may see something similar as the photo below.
 

Shade the area that reflects the temperature ranges you are looking for in growing spinach: 45-70F (7-24C). Note that in the illustration below.  There are two times during the year that are shaded. Yes!  You may be able to grow your crops more than once a year!

You will notice that if we were to follow the "textbook temperature range" we would have a very small window to sow spinach Sterling, VA (Zone 7) in the spring and another small window in the fall.  
 

In this article we provide some tips and tricks on extending this planting window. But to simplify the process of planning for now, we will stick to this short window.

Now let us look at the number of days it takes for a spinach seed to germinate (7-14), and add that window to our Planting Calendar.  

If you look at a region with a lower latitude, such as Ball Ground, GA, you will find that the window for growing spinach is much wider.

Take a look again at the your spinach information and factor in the days to harvest.  With this particular variety, it takes 40 days from the time of transplant to harvest your spinach. Add that harvest window to your calendar.  Here again are the examples for Sterling, VA and Ball Ground, GA.

In the case of spinach, the answer to the question, "Do I want this plant to flower?" is "No."

Simply Google "[Your zipcode] latitude."  In the case of Sterling, VA it is 39 N.

Spinach starts to flower when it experiences 13-hour (or longer) days. 

Look up the date when the number of hours in your latitude hits 13 hours. In the example of Sterling, VA at 39N, that would be around May 1st.

This would mean crossing out our entire harvesting window in the late spring / early summer because May 1st would be when this spinach starts bolting.

This makes spinach a tricky crop to grow in the Sterling, VA, where the window for growing spinach is small to begin with. 

It is slightly different in Georgia, where given it's latitude, 13 hour-days arrive around April 20th. Knowing that spinach will bolt after then, you would have to shorten the original harvest window in the spring. 

No both cases, however, continue grow spinach in the fall, when the daylight hours shorten, and a spinach harvest is more greatly assured. 

• Work out your own planting calendar by viewing the replay of The Planting Calendar, a workshop we gave a few years back.