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I'm planting Mammoth Red Clover as a cover crop -- it will grow all next year in a couple of my garden beds, and I'll plow it under the following spring (~18 months from now). I'd like to get it started this fall, but I'm wondering: how much time does clover need to establish before really cold weather hits?

I'm in NH, USDA zone 5, frosts start in September, ground freezes hard by December.

(I'd rather lose 8 months of growing time than lose all/most of the seed to winter kill.)

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I have no experience with Red Clover, but it sounds interesting -- Red Clover from University of Missouri Extension. From my small amount of reading, frost seeding might offer a better solution in USDA Zone 5 -- Frost Seeding & Whitetail Deer Food Plot Considerations (direct link to PDF, refer to page 2 of 5.) –  Mike Perry Sep 13 '11 at 3:45
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@Mike: Thanks for the frost seeding link. Sounds interesting, not sure if it would work here. We get heavy snowfall, this year I had a couple feet of snow on the garden on April 1. Usually by the time it all melts the ground is mushy, so the opportunity for sowing on frozen ground is lost. At that point, I'm better off planting into drills in the beds after they warm up a bit. –  bstpierre Sep 13 '11 at 12:44
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3 Answers 3

up vote 4 down vote accepted

There are two varieties of red clover that are grown – medium red clover (most popular variety) and mammoth red clover (what you're planning on using). According to this PDF from Penn state, the primary difference between the two is that medium red clover is quicker to establish than mammoth and grows back well after it is cut. The following is mostly information for medium red (as that was what was abundantly available) and most of it applies for mammoth, keeping in mind the differences pointed out*.

According to this article from Cornell university, red-clover is a slow growing crop. The seeding times suggested are in Feb/March for frost-seeding and between April to September. Frost-seeding, as Mike mentioned in the comments seems to be a good solution and according to the article he linked to, red clover is one of the easiest to establish.

Perhaps the best solution for you (taking into account the conditions in April and frost in September) is to plant late April/early May, towards the later stages of spring, but as early as possible. This article gives spring seeding a thumbs up:

Spring is the most common time to sow clover. This cover crop is often overseeded into small grain. If mowed at early flowering, it can provide nitrogen and cover through the summer, and even until the following spring.

The pdf from PSU also states:

The preferred time of establishment is in early spring or early summer, although establishing it after small grain crops come off is possible. The earlier the red clover is established, the more benefits it can be expected to produce the following year.

You should give the section titled "Establishment" in the article a further read, as it has a host of information that is tangentially related to your question.

Whichever variety you use, you should consider planting a nurse crop alongside, to aid the legume while growing by suppressing weeds (important since they're slow growing) and supporting it when it's covered by snow. The article from Cornell article suggests the following for a nurse crop mix:

For a nurse crop, mix 2/3 annual ryegrass with 1/3 medium red clover, sow 20-25 lb/ac.


*In addition, the second article I linked to also warns users not to use mammoth red clover as a cover crop (which is what you're using) although they don't say why. Might be something to look into (perhaps ask locally), and I haven't been able to dig up anything.

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Nice answer, thanks for the links. My choice of mammoth vs medium was random from the catalog. I'll pick the medium next time, and I'll work it into my rotation in the spring instead of the fall. –  bstpierre Dec 12 '11 at 0:50
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Plant them in late August to early September. This advice holds for most of the continental United States

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Update based on experience:

  1. I seeded one bed after peas came out, mid/late August. As of June the following year, the clover here is thick & crowding out most of the weeds.
  2. I seeded another bed after tomatoes came out, mid/late September. As of June the following year, the clover here is doing well, but not as thick as the August-planted.
  3. I seeded a bed this spring, late April/early May. The clover is up, but germination has been patchy (even with some watering to help when it was dry), and because the weeds (mostly grasses) look like they are going to out-compete the clover, I'm probably going to have to till the whole thing down (before the grass roots create a thick turf) and start again. (Given that it's June and we have warm weather, I may throw down some buckwheat and wait until August to retry the clover.)

This seems to confirm @jmusser's advice of August/September planting.

In retrospect it would have been helpful to have planted this spring's clover with some oats as recommended in @yoda's answer.

Also, it's worth noting that 2011/2012 was a very mild winter, and this may have benefited the pure stands of clover -- @yoda's answer also mentions that a nurse crop would have protected them from snowfall if we had gotten a normal amount.

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