When to plant heirloom tomatoes:Phenology and planting time of fruits & vegetables in a Northern Garden

Grandpa and Tesla
Grandpa and Tesla

Cris and I used to get quite a laugh out of his dear father, a salt of the earth man who loved to garden, fish and provide high humor for his grandchildren.  He was a man of strong beliefs, especially about his garden.  Potatoes must be planted on Good Friday; trees must be pruned on Presidents Day; and never plant anything during the full moon.

Before starting our small farming adventure 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 Willis Stainbrook’s folklore being espoused as a truth based on science and history.  Not 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.”

Spring Bed Ready for Tomatoes
Spring Bed Ready for Tomatoes

With respect to tomatoes (especially heirloom tomatoes)  a fairly specific rule of thumb in central Minnesota is to wait until memorial day to plant.  I do follow this rule to great success, but understand that my heirloom tomato seedlings  have been potted up into 4″ pots and have been fully hardened off, not little wispy things and not 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:

Cherry Blossoms in bloom
Cherry Blossoms in bloom
  •  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.

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 sitehttps://attra.ncat.org/attra-pub/viewhtml.php?id=44.  They have done a very comprehensive job of compiling the information in a scientific way.

Cris getting the compost in the beds
Cris getting the compost in the beds



For me, here in central Minnesota, I have committed the “truths” listed above to memory and hope to pass them on to my grandchildren also.

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

Author: Dorothy Stainbrook

I am a berry farmer and preserve-maker who runs a small farm and commercial kitchen in Forest Lake, MN.

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