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Best Time to Plant Tomatoes & Vegetables: (aka Phenology)

Best Time to Plant Tomatoes & Vegetables: (aka Phenology)

Old gardener stories are often based around a science called phenology. “Plant potatoes on Good Friday; prune trees on Presidents Day, and never plant anything during the full moon.” Homilies or science?

Cherry blossom tree signaling best time to plant vegetables in Zone 4
Cherry blossom tree signaling best time to plant vegetables in Zone 4

The Science of Phenology – when to plant

Before starting our small farm in Minnesota, I went to a number of classes, seminars and  basically anything I could find on organic farming.  I learned a great deal about soil, cover crops, organic disease control, etc. 

One of the seminars that was especially intriguing however, was a scientific lecture on Phenology.  I had never heard of it before, and I couldn’t believe it when I heard some of grandpa Stainbrook’s folklore being espoused as a truth based on science and history. 

Not necessarily the holiday planting lore, but some of the little things he used to do.  I’m sure if he was still with us and someone told him his knowledge was scientifically sound, he would respond “Pwiffwah,  everybody knows that.”

The National Gardening Association has this to say about Phenology:

Phenology has been used for ages in gardening and agriculture to determine when to plant, when pest insects will become a problem, and when plants will bloom. It turns out there is scientific basis for these observations. Modern plant scientists have found that phenology corresponds to a measurement called growing degree days. Growing degree days are calculated by adding the average daily temperature to, or subtracting it from, 50°F. This information provides a way to estimate the timing of certain events, such as when controls for pest insects need to be used to maximize their benefit.”

Best Time to Plant Tomatoes

Spring bed of garlic
Spring bed of garlic

With respect to tomatoes  a fairly specific rule of thumb in central Minnesota (Zone 4-5) is to wait until memorial day to plant.  

I do follow this rule to great success, but the caveat is that my heirloom tomato seedlings  have been potted up into 4″ pots and have been fully hardened off, not little wispy things that have been grown in a windowsill. Nor are they big honking plants that have already spent their energy coming to bloom.

Every time I have been fooled into planting early by a warm spring, a cold spell has followed and the plants are either stunted or they just sit there in the ground waiting patiently, but not growing.  The tomatoes planted on memorial day always catch up with any progress the early plants have made.

Here’s some other phenological pieces of planting wisdom that I picked up from that class or along the way:

Best Time to Plant Vegetables:

  •  Corn:  The ideal planting time for corn is when oak trees have emerged from dormancy and their young leaves have expanded to the size of a squirells ear (from the North American Indians)
  • Potatoes: Potato yields are largest if they are planted when dandelions begin blooming in open sunny spots (from the Irish-Northern farmers)
  • Peas:  Plant peas at apple blossom time (Kentuckians)
  •  Squash and Beans:  Plant them when the lilacs bloom
  • Perennials:  Plant when the maple leaves emerge from buds
  • Asparagus, Rhubarb & Strawberry:  Plant when the Plum trees bloom
  • Disease control for the Squash Vine Borer:  Cover squash and pumpkins with row cover when chicory starts to bloom and remove the cover after two weeks for pollination.
  • Control of Caterpillars & Gypsy Moth:  Spray with Bt right after they hatch, which is when the shadbush and redbud are in bloom.
  • Pruning Roses:  Prune when the Forsythia blooms
  • Morels:  When new oak leaves are the size of a squirrel’s ear… look for morels.

When using the earth’s signals to start planting, remember to harden your plants off first before you put them in the ground. This is important if you have started your plants indoors. Usually if you purchase seedlings from a farmers’ market or nursery they have already been hardened off.

For a detailed post on how to harden off your own plants started indoors, see this post.

Phenology is an aid to planning. When should you plant certain plants in your garden? When should you avoid bugs?  If this has peaked your interest and you want to get more in-depth information on phenology in your own area, visit this site  They have done a very comprehensive job of compiling the information in a scientific way.

Spring tilling in MN
Spring tilling in MN

For me, here in central Minnesota, I have committed the “truths” listed above to memory and hope to pass them on to my grandchildren, just like Grandpa Stainbrook (and I won’t call it phenology either!).

Farmer grandpa and grand-daughter
Farmer grandpa and grand-daughter

Now, go start “diggin dirt” as my son used to say.

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Tesla Stainbrook

Tuesday 29th of April 2014

That first picture is awfully cute!! :D

Dorothy Stainbrook

Tuesday 29th of April 2014


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