Why Vegetables Bolt Early in the Season

Credit: Flickr / Dag Terje Filip Endresen

Expert tips on when to plant to realize the very best harvest

Linda Gilkeson, as you may know, has been a frequent contributor to GardenWise, and is a well-respected expert on gardening in the Pacific Northwest. Read what she has to say about the beets that bolted in my garden last early summer:

In response to your article on bolting beets, I wanted to mention the V-word: “vernalization,” and how that relates to early plantings and growing seedlings to transplant into the garden.

The bottom line that is many vegetables respond to exposure to low temperatures 5-10°C (40-50°F) by flowering prematurely. They can only do this if they are old enough and big enough to have enough food reserves to support their flowering effort – but they can reach that point while they are actually pretty small.
 

Beets, cabbage family (especially cauliflower), onions, leeks, celery, celeriac, Swiss chard are among the most prone to going to seed if they are chilled as young plants. Ironically, because large, well-grown transplants are most at risk, gardeners that start seeds late or sow direct in the ground can end up with a more successful crop than people who go to the trouble of starting plants very early. I heard from one person last summer whose leeks all bolted to seed in their first season – but it turned out that she had done an unusually good job that year of growing big, sturdy leek seedlings – and they were large enough to vernalize in response to a period of cold late spring weather after they were planted out.

So don’t get too antsy to start your plants…some guidelines:

• The stem of cabbage-family transplants should be smaller than the diameter of a pencil when transplanted. If you are starting seeds indoors for cauliflower, broccoli or cabbage, sow about 6-7 weeks before you want to plant them out (late April). (I didn’t mention Brussels sprouts because I find it much better to start them in early June).

• Plant the smaller onion sets (about 1 cm/½ in. in diameter) and avoid larger sizes, which are the ones likely to send up seed stalks in the summer.

• For Swiss chard (and beets), I wait until mid- to late May to sow them directly in the garden when the soil is warm. The chard produces a crop all season, overwinters and continues to be harvested until June of the following year. By the time the next crop of chard (sown in May) is ready to pick, the old plants from the previous year are ready to pull out. With that planting schedule it is easy to have chard 12 months of the year without starting plants too early.

For those who want to know more, pick up Linda’s forthcoming new book, Backyard Bounty: The Complete Guide to Year-Round Organic Gardening in the Pacific Northwest. I just had the had the privilege of reading it prior to publication, and I highly recommend it!