You can substitute ground for seeds when using fenugreek. In fact, fenugreek seeds are often toasted and ground up with other spices for use in Indian and Middle Eastern dishes. But beware -- seeds and ground fenugreek have slightly different flavors and combine with food in different ways. So while it's possible to substitute the ground version for seeds, your dish won't turn out exactly the same.
The Need for Seeds
Fenugreek seeds are dark yellow pellets no more than a few millimeters long. Although the seeds are more bitter, ground fenugreek tends to concentrate flavor more than the seeds due to a larger surface area, so if a recipe asks for 1/2 teaspoon of fenugreek seeds, use approximately 1/4 to 1/3 teaspoon of ground fenugreek.
Toast With the Most
If the recipe calls for untoasted fenugreek seeds, then ground fenugreek may not provide quite the same level of bitterness. Ground fenugreek typically comes from roasted and ground seeds. Once roasted, the seeds have a sweeter, more celery-like flavor. They even feature in some Indian sweet delicacies known as laddoos. Check your recipe -- if it suggests roasting, then grinding the seeds, then substituting ground fenugreek should produce a similar result.
Whether ground or in seed form, fenugreek has a pungent, spicy and powerful taste. The "Good Food" Channel suggests that you need only 6 to 8 seeds to flavor a dish for four people. When it comes to using ground fenugreek, add a small pinch at a time, then taste the results. It's easier to add a small amount more than to take some away.
Leave Those Leaves
While fenugreek seeds and ground fenugreek can usually be swapped for each other, fresh fenugreek leaves are a different matter. Fenugreek leaves have a sweeter, far less bitter taste. They're often used like spinach or chard in Indian curries and stews. If a recipe calls for fenugreek leaves, neither seed nor powder will achieve the same result, and may make your dish too bitter.