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I have a potted Rosemary bush, purchased in the current pot a little over a year ago. It did well over last summer & this past winter, producing new growth after being pruned for kitchen use. As the weather transitioned from cool (zone 10a San Francisco bay area) to hotter summer temps in the 80s I failed to step up my watering schedule adequately (now watering 1 to 2 times a week as needed over the past couple of weeks). I am currently assuming that lack of water is the cause of the rather poor state of the plant, but there may be other factors involved.

Other points to note:

  • I do not have the ability to plant it in the ground
  • I fertilize it every 3 months or so with a sprinkling of 4-6-3
  • I occasionally spray my clusters of potted plants with a Neem oil solution to fend off white flies, I've noted no other pests present at this time
  • It is in a sheltered location & gets ample mid-day to afternoon sun

My thinking is that I could prune it back severely to induce new healthy growth & that with appropriate watering, I can get it to make a recovery. Am I on the right track here?

rosemary1 rosemary2 rosemary3

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    I agree with the answers, but I suspect the basic problem is you don't realize how big rosemary bushes are, and the fact that they usually end up looking "dead" at the base of the plant. Really, this thing wants to be in a 3-foot-square container (or even bigger) to be happy. The size of pot you have was only meant for transporting it from a nursery to your garden, not for the long term! – alephzero Jul 12 '18 at 12:33
  • Just a warning when pruning Rosemary - the scent is very pungent, so be careful not to breathe too much of it when you start hacking away! – alephzero Jul 12 '18 at 12:52
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Your thoughts are on track, Renesis. Do you have a dormancy period in San Francisco? Do trees drop their leaves? It has been such a long time since I visited San Fran.

Assuming there is a 'dormancy' period I would wait until fall to do major pruning. Take 6" off the top now...work up to at least a third taken off before winter. Take no more than 1/3 off that plant.

I am thinking it needs up potting into a number 10 or 10 gallon pot. I am just guessing (along with hubby) this is a 7 gallon pot, yes? Anyway, at least 2 to 4 inches wider in diameter. No more. Potting soil, only. Raise the bottom off the surface it sits upon with rocks, pieces of tile. This guy loves drainage and is very drought tolerant.

I'd up the fertilizer a bit until dormancy then half of what you are doing for the winter. You don't have to worry about freezing temperatures, do you? Roots are the most fragile part of a plant, next leaves, next branches and trunks. Roots in pots are subject to temperatures most roots in the soil of a garden don't have to deal with. Too hot or too cold will affect roots of a potted plant.

Larger pot with fresh potting soil should make a huge difference as well as a light heading, pruning now. Plants ideally should be twice as wide as tall. Hedges and ornamental shrubs are pruned to 1:2 or at least 1:1 1/2. 1 is height and 2 is width. Do you have hedging shears? 2 handles, like big scissors?

I'd wack off a good 6" now, off the top flat. Level, then point the tips at the center of the plant (this is tough to describe). Imagine a line straight up from the center of the plant. Point the tips at a spot 6" above the flattened top on that central imaginary line. Keep that angle by pointing at that spot.

You are chopping from below the plant pointing the shears at that spot or whatever spot as long as you keep that same angle all the way round your plant. The handles are lower than the blades. Keep the blades tangent to the plant. The goal is to get your rosemary to be 1 tall and 1.5 width. This is a ratio. Rosemary tends to be more tallish than wide naturally so 1: 1.5 is reasonable.

After transplanting and firming that soil fairly well around the roots of your rosemary, soak that plant very very well. Now feel its heft. Rosemary appreciates about half that heft. Newly transplanted it should be soaked. Normally it should not feel that heavy. Keep testing the heft every day. It should take awhile for this newly transplanted plant and soil to dry.

I simply push a pot with my foot. If it easily moves or tips that plant needs water. If it barely budges I would wait to water. You'll see or rather 'feel'?

Fertilizer. I like those numbers. Single digits makes sense as long as you know what to look for from the plant. Higher numbers get dangerous. I do like Osmocote 14-14-14 extended release. This 'applies' fertilizer over a period of time. 4 to 6 months for plants in pots.

I am seeing in your plant the thinning that comes from too little nitrogen, the yellowing of leaves at the bottom and the green leaves at the top. Nitrogen is a mobile chemical (some call it a nutrient, not me). That means when the plant has limited resources of nitrogen the plant will mobilize nitrogen from the lower leaves that don't get much sun anyway to the most productive leaves at the top.

When you transplant into fresh boring plain potting soil, add more of an even numbered formula. Dr. Earth's All Purpose 5-5-5 impressed the heck out of me this year. Great fillers with bacteria and fungi that are great for potted plants out of doors. Osmocote works well just do half of the directions. Make sure the potting soil you purchase is the cheapest. The expensive soil will have fertilizers and/or moisture holding gimmicks (gels, sponges) added that you do NOT want. Leave 1" between the surface of firmed soil and the rim. No less and no more. Helps with monitoring the watering.

I most certainly can explain this better if necessary. Working on an application to be able to 'sketch'...then send with answers. Not what I was hoping for or I need practice?

UPDATE.

Renesis I am amazed, you totally understood. What a beautiful diagram!! Wow. You are also correct that propping up your pot helps drainage big time!

Diagram added below: rosemary pruning

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    Thanks a lot stormy. For a living I do CAD based work (computer aided design) so if I have time tomorrow while I am at work I'll see if I can sketch up my interpretation of what you are trying to convey with your dimensional recommendations (not sure what a good way to share that sketch with you would be though...) FYI, the pot is 12" tall x 11" dia (So appx 4-5 gallons) & the plant is about 24" tall x about the same dia. I'll reply in more detail tomorrow too. – renesis Jul 12 '18 at 3:55
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    Excellent. I was well into designing by hand when CAD came out. I like the more relaxed lines for selling plants, the plans don't feel carved in stone. For you to draw what I've tried to explain would tell me oh so much about how I am communicating via the word. I LOVE black boards and chalk, sigh. Ink and paper and pens. I am geared eye, hand, paper....not through a key board. I see in 3 D from a 2 D plan...or whatever. Thanks, Renesis! Tomorrow...I'll be looking out... – stormy Jul 12 '18 at 4:03
  • Good advice from @stormy, though I would respectfully disagree on one point. At one of the sites I visit there's a rosemary thriving in pot that's about half as big again as yours. This pot is resting on the ground and consequently the roots have grown through the holes in the base of the pot, which I'm sure is why the plant is doing so well. So, I would repot yours into a bigger pot, and place it somewhere it can be left undisturbed for the roots to penetrate the ground. – Peter4075 Jul 12 '18 at 7:34
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    Sure stormy! & yeah, looks like I have a re-potting project for this weekend. – renesis Jul 13 '18 at 2:49
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    Pruned & re-potted today, a larger pot than I wanted, but it was the closest I could get, 16" dia. Apparently none of the stores around me are selling plain nursery pots any more... The plant was somewhat root-bound (unsurprisingly) so I did break up / trim the base a little. I'll update in a a couple weeks with a status & accept this answer unless I totally just killed it ;-) BTW, hope you don't mind, I'm going to edit the diagram I drew into your answer :-) – renesis Jul 14 '18 at 23:39
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Well, here's a somewhat different answer for you to ponder! Rosemary is a mediterranean herb - it grows well in fairly poor, free draining soil in full sun. Yours definitely needs a larger pot, and I'd suggest you prune back the mostly dead parts at the time of repotting. I would not, though, recommend any further fertilizer - this plant has meagre fertilizer needs, and you've been giving it fertilizer probably too often already, plus the new potting soil you use will have some small amount of feed within it which will be sufficient ongoing.

These are medium sized shrubs in the ground, reaching 6 x 6 feet or more - it will not be a permanent plant in a pot, there will come a point where it will outgrow any pot you provide for it, although you will likely have it for up to 5 years, maybe more if you provide bigger pots ongoing.

Fertilize in spring with a slow release granular balanced fertilizer (NPK something like 7-7-7); you can either leave it at that till the following spring, or repeat the fertilizer 6 weeks later, depending on the recommendations of the product you choose, but keep it watered as necessary, allowing the pot to drain down freely to get rid of excess water. Raising the pot off the ground by sitting it on something (pot feet, bits of slate or whatever) will help with drainage. Note that Rosemary hates wet feet in winter, so if you have very wet winters, that might be an issue.

In terms of insect infestation, Rosemary oil is a natural insecticide so the plant is largely untroubled by most insects, other than Rosemary Beetle and occasionally a mite infestation, so you do not need to apply neem as a preventative measure.

  • I am looking at a plant transferring Nitrogen from the lower leaves that don't get the light to the top of the plant that does. Yellow interior, nice green only on the top. I am not seeing any yellowing of the top leaves/canopy. Keeping a plant in a pot will automatically keep the plant at a size relevant to the size of the pot. Trees in the natural world say, get 100' high? Trees in urban situations will only get 30 feet high. All plants have to have NPK added to potting soil and almost always to garden soil. Soil does not come with chemistry for all the plants we humans want to grow. – stormy Jul 12 '18 at 21:23
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    @stormy my answer is not meant to be a criticism of yours, so you don;t need to explain or defend it. I'm fully aware that, in the States, you use far more fertilizer than we do here, but the advice I've given is, nonetheless, still my advice: it was what I meant to say in the first place, and it still is. – Bamboo Jul 12 '18 at 21:44
  • Thanks Bamboo. Noted on the Neem oil. Really i just tend to give all my potted plants a spritz, mainly aiming for the chilis, strawberries, chives etc. & well, if there is some left in the bottle I spray the others even if not really needed (rosemary, fig, thyme... CA Grey Pine...). Back to the Rosemary though, never had a problem with water sitting at the bottom of the pot, but thanks for the note. I can go to a bit bigger pot, but probably only once, after which I assume I'll have to trim the roots if it becomes bound. – renesis Jul 13 '18 at 1:16
  • Ohh, PS, Rosemary is actually quite common in municipal & commercial landscaping around here, so I do quite often see it at the 6'x6' size you mention. Prior to living here, I have to admit that I thought rosemary was a small herbaceous plant on the scale of basil or something! – renesis Jul 13 '18 at 1:33
  • @renesis well you're not alone in thinking it was small, like basil - I thought the same years ago before I got into horticulture! – Bamboo Jul 13 '18 at 16:53
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And here is another answer, so many different experiences...

Likely since the plant is so mature the root system is very extensive, filling the pot; vigorous roots and successive waterings have displaced the soil to the extent that there is very little soil left to act as a spongy reservoir of moisture, so the plant is always in a state of looking for water no matter how carefully irrigated. If you could examine the roots (roll the pot onto its side, then knock the pot away from the plant) you would see roots in a big mass with little soil.

I would prune back the top by half (preferably taking out some of those large thick branches at the base) and using an old carving knife or garden spade reduce the root ball from the bottom by about a third to a half. This will make the plant and root ball a lot more manageable. Put fresh soil in the pot so that when you replace the plant it is sitting comfortably high. Finish refilling the pot and water. Then you are good for about two years, at which point repeat the process until the trunk is so thick you could use it for firewood. The advantage here is you keep the plant in the same size pot.

Take half a dozen cuttings about five inches long and strip off the lower leaves and stick in soil (commercial or plain garden soil if it is anything but pure sand or builders rubble) in a single four inch pot evenly spaced around the rim. Keep moist and within about 3 weeks in summer time you will have healthy replacements coming along for when you tire of the old large plant.

  • I pruned & re-potted today, mostly per stormy's answer, but did find (unsurprisingly) that the roots were a bit bound. I upped to a 16" pot & did break up the bottom of the root ball, just not as much as you suggested , as I was moving to a bigger pot. In the future, I will not be moving this plant to a larger pot & may trim the root ball more as you suggest. – renesis Jul 14 '18 at 23:32
  • Once a plant gets to a certain size as a potted plant growth slows down to be survivable in its...situation. Harmony, happiness and healthy plants. Making plants into Bonsai isn't necessary. Some of the same ideas apply but a 30 foot high and wide tree maximum potential will be very happy at 8X8' in a 4X4' pot for decades, without root pruning. Plants know they'd be better off staying smaller in a pot. I don't 'trim' roots off as much as just break up the circling roots knowing those broken roots will be more able to promote fine feeder roots. Cleaving woody perennials is risky. – stormy Jul 16 '18 at 7:10

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