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Why We Remove Garlic Scapes (and why we don't)

Garlic growers know that the best ways to make their garlic grow larger are to: water it well in spring, mulch to keep the moisture in the ground, and... remove the scapes. "Scapes" are the flower stems that grow in June, and conventional wisdom is that they draw energy away from the underground bulbs, so removing them make the bulbs grow larger. We thought we would test that theory, and here are our results.

What are garlic scapes?

Scapes are simply garlic flower stems. Garlic is related to tulips and daffodils, and like those it blooms in the spring. The flowers are not showy, but they are edible, so garlic growers usually cut the stems off in June. When they're young enough that you can easily snap them with your fingers, garlic scapes can be cooked in a great variety of ways, just like onion greens.

Another reason that growers prefer to remove scapes (even if there are more than they can eat!) is that the plant has to divide its energy between growing the scape at the top and growing the bulb underground. It makes sense that if the scape is removed, the plant can concentrate all its growth into the bulb and grow it larger.

At Seeds of Diversity, we actually let the scapes grow. The reason is that the garlic flower contains several small "bulbils", tiny garlic bulbs, that can be planted to multiply the variety exactly. There is no cross-pollination with bulbils, so several different varieties of garlic can be grown side-by-side and their bulbils will grow true to type. That's the main way that we distribute garlic varieties to growers from coast to coast, and the bulbils have to ripen all the way into August.

Our experiment

Although we want to grow lots of bulbils every year, the theory behind scape removal was so intriguing that we decided to test it. We grow 68 varieties of garlic in our collection, and 55 of those produce bulbils (the other thirteen are softnecks that don't bloom where our main collection is grown in Ontario). We grow 24 plants of each variety, which gives enough to replant, plus a lot of bulbils. In each plot, we removed the scapes from half of the plants in June, leaving the other 12 to grow bulbils all the way until harvest in August. Then when we harvested the bulbs we put the scapes-off and scapes-on bulbs in separate bags, let them cure, cleaned off the soil and roots, and weighed them.

That was a lot of extra work, and thanks to our volunteers and garden partners who helped!

The result: on average the bulbs that had scapes removed were 23% heavier than those that had grown up all the way with scapes on.

That was less of an average than we had expected, because previous ad-hoc measurements had shown a much larger difference. But the average here is deceiving. Some varieties had increases of 50-60% and one was more than double-sized with the scapes removed. However, 16 varieties actually grew smaller without the scapes. That defies the common-sense principle that the plant divides its growth, and it happened in too many separate measurements to seem like a simple error.

So we'll try it again, and keep asking questions. Like:

• Do the same variations in size happen the same way every year?
• Is there some common trait among the varieties that grew larger or smaller? e.g. the category of garlic, or structure of the scape?
• Does weather play a factor in how garlic responds to having scapes removed?

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