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Garden Calendar for May


Contributors: Michelle Grabowski and David C. Zlesak

May is a busy month with lots of gardening fun to be had.  After a long cold winter, the excitement of getting out and enjoying our gardens feels like a reward. 

Enjoy the many spring flowering shrubs (bridal wreath spirea, forsythia, lilacs, flowering almonds, etc.) and wait to prune them, if necessary, until after they are done flowering.  Pruning them before they flower would ultimately most benefit the plant because they wouldn’t be investing their stored energy in new growth that would soon be cut off.  However, after waiting this long for those beautiful flowers we don’t want to miss them! 

New growth is starting on most of our herbaceous perennials.  If one hasn’t cut back last year’s stems, now is a great time to do so before the new growth gets larger and interferes with removing the old growth.  Come spring, last years stems tend to be more brittle and tend to be easier to remove than last fall.  Many times pushing them a bit from side to side will allow them to cleanly snap at the base of the plant without even needing to physically cut them.

Photo 1: Lilac flower buds are swelling and will soon be open. David Zlesak


Continue to plant your cool season vegetable crops.  This includes direct seeding of peas, spinach, and lettuce and planting of onion and cole crop (broccoli, cabbage, cauliflower, etc.) transplants. There are many different onion varieties on the market.  One thing to try to look for are those that are long day adapted varieties.  These develop and invest their energy into their bulbs as the days are long, like we experience in our Minnesota summers.  There are also short day onion varieties that bulk up as the days get shorter.  These typically do not perform that great here in Minnesota as by the time the days get shorter in fall the growing season is close to its end.  Many of the onion sets we find for sale in stores are of short day varieties as these are easily grown in Southern states for us during the winter months.  The will grow somewhat in size after we plant them here in Minnesota, but do not compare to the growth potential of adapted long day varieties.  Many garden centers have little packs of seedlings of adapted long day varieties.  Such varieties include: ‘Walla Walla’, ‘Mars’, and ‘Ailsa Craig’.

Photo 2 (right): Remove last years stems as soon as possible before new growth makes it more difficult to do so. David Zlesak

Photo 3 (left): These young seedlings of 'Walla Walla' onion will grow well in our long summer days. David Zlesak

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