Leek is a vegetable that belongs to the Allium family. The genus also contains garlic, onion, Chinese onion, chive, shallot, scallion, kurrat, and elephant garlic. These are all closely related vegetables with varying taste, flavor, and fragrance. There uses in food also differs.  
Leek has a long cylinder of green leaves bundled in a sheath with a dense white base at the bottom. The whitest bulb at the base is most commonly used in dishes. However, the leaves too can be added to soups, stews, and salads. 
Leeks taste like onion and garlic with a distinctly milder flavor and rich texture than them.
You may think of substituting leeks in your dishes—when it is out of season and not affordable due to its relatively higher price.
Other vegetables of allium family make good substitutions for leeks. Though you cannot expect them to give out the exact flavor of leeks in your dishes, the alternatives can save your day.
Here are 6 substitutes of leeks that you may try.
6 Leek Substitutes That You May Try
Onion is the most widely cultivated vegetable of the allium family. You can easily find it at local groceries at all seasons. It’s cheaper than leeks.
Onion has a stronger flavor and fragrance than leeks. But the bulb can provide similar bulk and texture to your dishes. There are different varieties of onions. Red and white onions may not come close to leeks flavor. So you should look out for yellow onions. As a rule of thumb, saute chopped onion to sweeten the flavor before adding them to your dish. 
For 1 cup of leeks, you may replace ½ cup of chopped and sauteed yellow onion.
2. Scallion or Green Onion
Scallion or green onion can be the closest substitute for leeks. It is also known as spring onion or salad onion. Scallion doesn’t have fully developed bulbs as the leeks and mature onion.
However, you may use the raw green leaves as an alternative to leeks in your salad garnish and soups. Scallion has a sweet and juicy flavor as mild as leeks.  You can replace 1 cup of chopped or sliced scallion for 1 cup of leeks in the recipe.
Shallot is another close substitute for leeks. It is a type of onion with a slightly milder taste and texture.  So, its flavor comes close to leeks. Fresh shallots are widely available in all supermarkets.
You can use sautéed or raw thinly chopped shallot as a substitute for leeks.
Add less amount of the ingredient than what’s in the recipe. A good rule of substituting shallot for leeks is to replace 1 cup of leeks with ¾ cup of shallot.
The old English term for garlic is garlic which translates to ‘spear shaped leek.’
Garlic is another close relative of leeks with a more intense smell, pungent flavor, and taste. 
Garlic is easily available and cheaper alternative to leeks. To retain the delicate flavor of leeks, you replace it with a small amount of chopped and sauteed garlic in the dish.
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5. Ramps or Wild Leeks
Ramp is getting popular as a culinary ingredient in the North American restaurants. It is an early spring vegetable that grows extensively in the eastern U.S.A and Canada. Ramps look alike scallions, but they have smaller bulbs and one or two light-green, smooth leaves. The ramp has a distinct flavor that is milder than leeks. It has a pronounced onion smell and strong-pungent garlic-like flavor. That’s why the vegetable is easily adaptable in various dishes. 
Ramps are easy to clean and prepare. The freshly chopped ramps can be used in all traditional dishes that call for leeks or scallions. Ramps make a good substitute for leeks in scrambled eggs, soup, rice, bacon, and potato dishes.
6. Frozen Leeks
Frozen leeks may be available in the freezer section of many supermarkets or groceries. It makes an easy replacement for fresh leeks. Because it’s already chopped it saves preparation time and there’s no wastage. You can add it to your soups and casseroles just the way you use fresh leeks.
Leeks belong to the onion family with many other vegetables that closely imitate its flavor, texture, fragrance, and taste. You can always substitute leeks with any of the alternative vegetables discussed above.
However, many of the substitutes have slightly more pungent taste and flavor than leeks. Make sure you add less amount of the replacing ingredient to retain the delicacy of leeks in your dishes.