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Some Mid-Fall Notes

Thymus serpyllum 'Pink Chintz', flowering thyme

This week’s blog entry from your hip, non-hipster main street gardener is a collection of thoughts and answers to questions I recently received. Mostly, it’s about things needing attention as we enter mid-autumn.

It has been one of the most spectacularly enjoyable fall seasons in recent memory, in my opinion. Many of the autumn colors were particularly vibrant and long lasting, thanks to warmer than usual days with cool nights. Often, we get a week or two of good foliage color and a cold, windy day strips all the joy out of the season, but so far, we haven’t had that day.

Though the warm stretches we experienced lately are great for humans, they can be difficult for recent new plantings. The best insurance against winter kill for any perennial is to make sure they are getting an inch to an inch and half of moisture per week. This is especially true for pines and broadleaf evergreens, and for newly transplanted material which has not been established yet.

Every year, I am asked how late can someone plant perennials. The answer it depends on many factors, including:

The earlier in fall one plants or transplants, the greater success one can expect in spring wake ups. The longer the root system has to dig into the garden soil, the greater chance of surviving the coming cold. One would think that once the ambient air temperature turns frigid, one’s days of planting are over, and with them, the hope of getting those last-minute-at-the-garden-center-deals-that-were-too-good-to-pass-up into the ground. But wait, there’s still time! A gardener still wanting to plant just needs to take more precautions as the season progresses. The key is keeping the soil warm enough, long enough to get roots established. Though growth above ground halts with successive frosts, there is still a lot happening below ground. Roots keep growing, expanding, and doing their thing.

Last year, I faced a dilemma of large proportions. I was sitting on an expensive inventory of ornamental thyme destined for the Island Garden, and planting was suddenly halted with a freak snow at the end of October. I had to shut down planting operations early. Thyme out of the ground is only hardy to thirty-two degrees. I was faced with losing a lot of plants and with them, a lot of cash. As documented in previous blog entries, we tried various means of winter protection, and all of them failed to work. I was forced to plant about half of the remaining thyme in early December as the snow was again flying. Some of the root balls were literally chunks of ice inserted in the ground, yet looking at the plantings now, you would never guess. We covered the ground about to be planted the next day with concrete blankets to keep the ground just soft enough to work. Once planted, we placed a layer of wood chips on top to insulate the ground. That insulation kept the ground warm enough, long enough, to successfully over winter the plants. The proof is in the picture above: the thyme thrived and looked spectacular this spring! If you plant late, water well and temporarily mulch with a fluffy mulch.

This brings up a side note, a pet peeve of mine. I hear from people wondering when is the best time to plant spring flowering bulbs such as tulips or daffodils. You can plant bulbs practically any time, but there is one risk to planting too early in the season and it is not the reason I usually hear. It seems like every year I hear people warning others to not plant their tulips too early because you do not want them to come up only to get nipped in the cold air. I have news for you. That ain’t ever happening. Daffodils will emerge a bit above ground, as I have discussed in the past, but tulips can not emerge too early. They must go through a certain length of time (called chilling requirements) below certain soil temperatures and moisture levels in order to break dormancy. I will give you a hint: that requires a solid winter period. The real danger to planting spring bulbs “too early” is actually rot. A bulb may rot out from too much moisture when it is not established. However, it can dry out in the bag wherever you’re storing it too, so keep that in mind as well.

Okay, back to my main discussion and my last thing to note at the midway point of the fall season: what to do with fall blooming perennials such as mums and asters. There is not total agreement on whether to cut mums and asters back completely in the fall or spring. I have always cut my fall blooming material back in the spring for a couple of reasons:

  1. Allow the foliage to remain to put a bit of energy back into the plant after the exhausting bloom season. 
  2. Prioritizing what I have time to cut and tend to in the garden. Leave some plants for early spring work if my fall is really packed.
  3. Winter protection. This is a somewhat debatable reason. Stems left standing tend to keep snow away from the crown a bit, thus offering some protection, however there are plenty of perennials that come back just fine after I cut them back to the ground, without stems to stave off the white stuff. 

I think that clears out the laundry list of timely gardening notes I wanted to share, so until the next riveting edition of this blog I say: get planting!

Josh Steffen, Horticulture and Facilities Manager

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