Do you need to buy it? Unless your soil has been extensively farmed and depleted, it exists naturally.

You can order them from almost any gardening catalogue. But do you really need them? https://www.gardenmyths.com/mycorrhizae-fungi-inoculant-products/

Many "premium" fertilizers claim to contain it, thou I don't know if it really makes a difference in the long term. Suppose it doesn't hurt either, just if you want to spend some extra money.

Dr. Earth Vegetable Fertilizer

I saw a video from the Netherlands and they used it . https://www.youtube.com/watch?v=eVuxEZ9BH0o

I wanna make some of my own potting soil. I have coir, peat moss .. what is a" wetting agent"? it mentioned on a package of potting soil I bought today... thanks all

Mycorrhizal fungi are not essential for any container plantings. The same reasons that container gardening requires a completely different approach from inground gardening is also the reasoning behind the unnecessary application or inclusion of these fungal amendments. Mycorrhizae act as extensions of a plant's root system to access soil nutrients, moisture and oxygen. A well constructed potting media will have the necessary aeration and moisture retention for good root development and attention to watering and fertilizing will make sure all necessary nutrient needs are addressed.

Also, there are thousands of species of mycorrhizal fungi and different plants will benefit from different species. Most mycorrhizal inoculants only offer a small handful of species that may or may not have any impact on what you are growing anyway.

IMO and that of most horticulturists, they are a vast waste of money!!

If you want to make your own potting soil, read up on the 5-1-1 or gritty mixes discussed at length on the Container Gardening forum. They are far superior to anything you can purchase and no need for wetting agents, mycorrhizae or any other expensive but completely unnecessary additives.

Before you do buy any, please read this: https://www.gardenmyths.com/mycorrhizae-fungi-inoculant-products/

And this: https://joegardener.com/podcast/decoding-garden-advice/

Specifically:

Adding mycorrhizae to your soil will make a powerful difference in the health of your plants. DEBATABLE

It’s true that mycorrhizae provide benefit to your plants. These fungi work synergistically with plant roots to collect and provide them with water and nutrients. In return, the plant provides the mycorrhizae with carbohydrates as a food source. This exchange does allow your plants to take up more nutrients.

However, mycorrhizae are extremely sensitive to environmental changes, so mycorrhizae sold commercially or promoted on soil packaging are usually dead. As they were transported, they were subjected to varying temperatures, and they just can’t sustain in those shifts.

Let’s say for argument’s sake, the mycorrhizae you purchase did manage to survive the journey. Will they boost your plants? Maybe not.

There are many types of mycorrhizae, and they all perform slightly different work with different plant types. So, the mycorrhizae you import may not be the type your plants will benefit most from – and in some cases can do harm. Odds are better that the mycorrhizae, which are nearly always present natively, will provide all your plants need.

Solution: If you find a great deal on premixed soil which includes mycorrhizae, buy it. The fungi are likely dead, but you got a good deal on soil – count that a win. Just don’t spend your hard-earned money specifically to buy soil featuring mycorrhizae. It’s not worth it.