Old dutch who lived in St. Paul, Mn and posted here never mulched his garlic and grew a crop every year but they were small. Mulch will minimize the heaving of the cloves in cold climates, this action will break the roots already grown but won't kill the clove and just delays the spring growth a bit while developing new roots resulting in a high percentage of small bulbs.

If your ground doesn't freeze no heaving will happen so NO you don't need to mulch, and even if it does freeze, NO you don't need to mulch and you'll just get a lot of small bulbs. But the mulch will help keep the ground from drying out and keep the weeds out. Garlic is a heavy feeder and can not compete with weeds at all, and mulching is what makes growing garlic the easiest thing to grow. No, you don't need to mulch but I suggest you do it anyway.

Well, I prefer getting large bulbs. Weeds are not a big deal in my garden, as it is an urban one, surrounded by lots of lawns. As I say, I never mulch my onions, and they grow big. Ground freezing NEVER happens here, even when we get an unseasonably cold spell. So given all that what is it specifically about mulch that makes bulbs larger?

Mulch helps in the winter for freezing areas with heaves and desiccation. In some warmer places, it can help protect the plants if they have tipped up and there are cold spells. It helps in the summer by keeping the soil moisture content and temperature more even. It can also help as a light stabilizer for the necks through sprouting and development if there are winds. And weed control. In general, these small things can make the garlic a bit more comfortable to grow bigger.

OK it sounds for me as if mulch is somewhat useless for me right now, but in the heat of the summer (and these garlics won't be harvested until late summer), it might have some value in moisture retention. Still not completely clear why something that is bad for onions is good for garlic.

Some gardeners find benefit from mulching onions too. For some of the same reasons as garlic. However, onions are planted at a different depth than garlic. Onions tend to bulb up more from the soil, while garlic tends to head completly below the soil. So while some mulching between onions can be a benefit for some gardeners, it also can be a problem because onions don't like their shoulders being buried after they start to bulb up out of the soil. Some gardeners take the time with their onions to spoon them to ensure the bulb is clear of anything.

Garlic and onions are similar in ways since they are both alliums, but they also have some different needs to grow their best.

Never once have I read that mulch is bad for onions. Keeps soil moisture in, keeps soil temps stable, prevents weeds, helps feed the soil... All benefits. I've always mulched them. Same with shallots, garlic, and leeks. The benefits of mulch far outweigh any supposed downside.

The only difference I can see that *may* give credence to onions not liking mulch is that onions typically bulb at least partially above the soil surface. Garlic bulbs completely underground so mulching won't impact bulb size in any way, as the bulbs are already buried/covered.

Rodney

Well, there are lots of cautions online about mulching onions. The issue seems to be that exposure of onion bulbs to moist material encourages bulb rot. The places that do suggest mulch often caution to keep the mulch away from the bulbs. Doesn't make a lot of sense because the soil is at least as moist at the mulch! True that the garlic bulb is wholly underground, so it isn't exposed to mulch but, as I say, it sure isn't obvious what mulch does to bulbs that moist soil won't. That all being said, plastic mulch is often recommended as that doesn't promote bulb rot and yet preserves soil moisture. Yes, I can't see why mulch would influence bulb size, in any case.

Keeping soil moisture in is good but, for me, that's wholly a summer issue. My soil temp almost never gets below 50F so that's not a worry. It's not just that the air temp doesn't get very low, but also my soil is pretty organic-rich, so there is in-situ composting going on, adding heat. As I said, weeds are really not a serious bother for me. Vastly better ways to feed that soil than with mulch. I use nitrate fertilizer. As the mulch breaks down, soil friability can be improved, but I dig in loads at the beginning of the season.

I did find this interesting writeup, comparing mulchability of onions and garlic, but it seems to be relevant mainly for cold protection.

https://greenthumbgardeningsecrets.com/speaking-of-mulch-contrasting-alliums/

Somewhat curious why cold protection is highlighted here for garlic but not for onions.

If you are curious why the author wrote the article they way they did, there is an option to leave a reply at the bottom of the page there. You can ask them. There may be various reasons for the author to write as they did.

Gardening literature is full of contradictions and inconsistency. I'll let it ride. Especially for a post that is many years old.

In colder regions gardeners plant garlic in the Autumn to overwinter for Spring, while onions are planted in Spring after the low temps of Winter. So cold protection is highlighted for garlic. The author doesn't specify where they are gardening.

That does make some sense. Up north, onions are best planted in the spring. Why not garlic as well? True that garlic has a longer DTM than onions, so you might like to get garlic started earlier to mature in the summer.

Planting garlic in spring can be done but the bulb size suffers. If left in the ground to its own devices you will see that garlic has a natural cycle of sprouting in the fall, overwintering, growing like crazy in early spring (basically as soon as the ground thaws), bulbing by mid summer, going dormant, and then sprouting again in fall. By planting in spring you are not allowing the garlic to establish roots in the fall and you are putting it behind. Even if you plant "as early as the ground can be worked" it will still be behind a fall planted clove, as the fall planted clove will most likely already be putting on new green growth or about to be when you are finally able to plant a clove in the spring.

Rodney

Thanks. That's useful to know. I think that's all connected with the fact that the DTM for garlic is longer than for onions. They need some time in the ground to form good roots before they start growing fast in the summer.

Since garlic is a perennial I see it more as following the natural growing cycle, which is why I mentioned its growing cycle in my previous comment. Garlic is going to bulb up around the same time whether you plant it in spring or fall. Daylength triggers it. If you try to plant garlic at the wrong time, i.e. spring or summer, you are going against its nature and will be disappointed in the results.

Rodney

Same case for onions. Daylength triggers bulb growth for them as well. For me, short day onions planted out in November start bulbing in March, and harvest in May. Long day onions up north won't start bulbing until June, So it makes sense to start those outside maybe in February for harvest in August. My understanding is that daylength requirements for garlic is similar to short-day onions, so if I plant in fall, I assume they will also start bulbing in March/April. But the bulb development must be slower, because they won't get harvested until July or August. I have to assume that's why garlic needs to be planted early, or else bulbing will have to endure winter.

I never do

Ya gotta be careful in making generalizations. Garlic that folks grow up here (upstate NY- hardneck, fall planted) very different culture than what you woyld grow (softneck, spring planted)

Um, you want to be specific about that? How are mulching strategies different for hardneck and softneck? I might imagine that in a very cold climate, some frost protection for roots might be advisable, and deep mulching could help with that. This was alluded to in one of the first comments here.