Green Thumb Tip # 6: Size Matters!

Magnolia grandiflora growing along the Colonial Parkway near Jametown, VA.

Magnolia grandiflora growing along the Colonial Parkway near Jametown, VA.


Have you ever planted a sweet little plant that you fell in love with, only to find yourself in pitched battle to control it a few years later?  It has happened to most of us at one time or another.  Sitting at the nursery in its little pot, it looked so charming.  You knew the perfect place for it….


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But just like babies and puppies, plants grow when they’re happy.  And quickly! 

I believe that many people hate ‘gardening’ because of their many battles trying to control a gargantuan shrub or spreading perennial which has gotten out of control.  ‘Mature size’ matters!  Both the expected height and the expected spread of an adoptive plant need to be considered before you invite it home to your garden.  And this information isn’t always accurate on the tag or easy to track down!


Crepe Myrtle begins to bloom in our garden, and will fill the garden with flowers until early September.

Crepe Myrtle grows very fast and most varieties will send up suckers beside the main stem, gradually growing into a wider and wider clump. 


It is wise to consider, before the purchase, the size of your space.  How wide can this plant comfortably grow without hitting the house or bumping into other structural plants?  How high will be too high?  Will a shrub eventually block windows or grow out into your driveway?  Will an herb or perennial take off and steal the entire garden with its runners?


Cannas spread by underground rhizomes and grow thicker each year.

Cannas spread by underground rhizomes and grow thicker each year.  A few plants quickly spread to form a solid stand.


I can’t tell you how often I’ve seen ignorant ‘landscapers’ plant Magnolia trees as foundation plantings for office buildings.  Now, understand that our native Magnolia grandiflora will grow more than 100′ tall and 30′-40′ across at maturity.  Somebody didn’t think something through when they plant a young tree of this size less than 10′ from a brick wall….

So before you purchase and before you dig that hole, do a little research into what that plant will be 2, 5, and 20 years from now.

Maybe you’re thinking, “But I have electric hedge trimmers… it doesn’t really matter.”  Yes, and no.  Some plants will respond to regular trimming with more growth and can be maintained at a certain height indefinitely.  But others, like many conifers, will never recover from a shearing or improper pruning.  Others will just grow so fast, once established, you’ll lose the race!  I’ve never enjoyed cutting back shrubs on a hot summer day.  Have you?


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This Rose of Sharon has grown from a shrub to a large tree. Although it has overgrown its intended space, we prune only the lower branches and simply enjoy the show!


Better to select a plant to fit the space you have.  While tags are good guides, you will find much more useful information from a quick internet search.  Often you’ll find university studies comparing cultivars of a plant to help you select the best one for your situation.  For example, if you want to plant an Azalea, you can choose from a dwarf variety which won’t ever grow more than 3′ high or one of the tall ‘Indica’ hybrids which may reach 10′ in just a few years. Often you’ll learn that expected height and spread depend on your climate.

Another important consideration is whether a plant will ‘sucker’ and spread.  This means that rather than growing from a single stem, new stems will keep growing out of the ground year after year, making your plant wider and wider with each passing season.  Some native plants, ferns, perennials, and even trees will just keep growing outwards like a rapacious bamboo!


A new bamboo 'shoot' emerged far from the bamboo forest, right in front of a fig tree. We cut this down after taking a photo.

A new bamboo ‘shoot’ emerged far from the bamboo forest, right in front of a fig tree. We cut this down after taking a photo.


Always check so you know what to expect, and how many plants may be needed to cover your real estate with a nice stand of these willing plants.  If you don’t want wide coverage, you may find yourself on the business end of a shovel digging up the new growth for many years to come.

So do a little research before you introduce a new plant to your garden, even if that new plant is a ‘gift.’  A professional plantsman once showed me a towering Rhododendron which covered half of the side wall of his home and reached for the roof line.  This monster, lovely as it was, originally came to the garden in a little gallon pot as a gift from a Rhododendron enthusiast friend.

There were originally two little shrubs in that pot, and they are planted side by side, one nearly twice as tall as the other.  Stunning for the weeks when they bloom each May, these two shrubs have grown completely out of control and remain on my friend’s ‘get around to it’ list for heavy pruning…..

The best of intentions can lead to later problems when you don’t pause to do your homework.


The march of the bamboo up the hill back in early May. We have had to control the growth up towards the garden.

The march of the bamboo up the hill in early May. We have had to control the growth up towards the rest of the garden each spring.


Woodland Gnome’s Caveat:  When a friend offers me a plant I nearly always accept it.  But I wait to plant it out until I first figure out what it is and then learn something about it.  If necessary, I’ll pot it up for a while as I do the research.  If I can’t use it, then I’ll find a gardening friend who can.  Since we all have different gardening goals and conditions there is generally someone glad to get it.  

And, when sharing plants from my garden with others I try to give full disclosure.  I want my friends smiling with fond memories as they admire the plants I’ve given, not mumbling unhappy things while they wrestle with the ‘gifted’ plant!  A little understanding goes a long way to siting a plant properly for years of enjoyment.


These white Monarda are performing well in partial sun. A friend gave me several clumps last year, and I spread them around in different parts of the garden to see where they would do well. These in partial sun, near mature Lilac shrubs, have done the best.

A friend gave me these beautiful white Monarda last year. I spread them around in different parts of the garden to see where they would do well, and shared a few clumps with friends.  Monarda spread quickly with underground stems.


“Green Thumb” Tips:  Many of you who visit Forest Garden are amazing gardeners with years of experience to share.  Others are just getting started, and are looking for a few ‘tips and tricks’ to help you grow the garden of your dreams.

I believe the only difference between a “Green Thumb” and a “Brown Thumb” is a little bit of know-how and a lot of passion for our plants.  If you feel inclined to share a little bit of what YOU KNOW from your years of gardening experience, please create a new post titled: “Green Thumb” Tip: (topic) and include a link back to this page.  I will update this page with a clear link back to your post in a listing by topic, so others can find your post, and will include the link in all future “Green Thumb” Tip posts.

Let’s work together to build an online resource of helpful tips for all of those who are passionate about plants, and who would like to learn more about how to grow them well.


The reddish orange flowers, Crocosmia, are another gift from a gardening friend. I've since learned that these are Iris relatives and form clumps, expanding each year. Lovely flowers, they are spread in different beds around our garden.

The reddish orange flowers, Crocosmia, are another gift from a gardening friend. I’ve since learned that these are Iris relatives and form clumps, expanding each year. Lovely flowers, and tough, they are spread in different beds around our garden.


Many thanks to Peggy, of Oak Trees Studios, who posted her first tip:  ‘Green Thumb’ Tip:  Release Those Pot-Bound Roots!  Please visit her post for beautiful instructions on how to prepare roots for re-potting.

‘Green Thumb’ Tip #1:  Pinch!

‘Green Thumb’ Tip #2:  Feed!

‘Green Thumb’ Tip #3 Deadhead!

‘Green Thumb’ Tip #4 Get the Light Right!

Green Thumb Tip #5: Keep Planting!

‘Green Thumb’ Tip # 7:  Experiment!

Green Thumb Tip #8:  Observe!

‘Green Thumb’ Tip #9: Plan Ahead

‘Green Thumb’ Tip #10: Understand the Rhythm


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Woodland Gnome 2016


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About woodlandgnome

Lifelong teacher and gardener.

11 responses to “Green Thumb Tip # 6: Size Matters!

  1. Ah indeed another important tip, WG! I have been thinking about this topic only today when I was planting out my newly-grown rhubarb seedlings in a perennial bed. The plants look quite small and widely spread out in their new bed today but, when fully grown, the leaves of each plant should only just touch the neighbouring one. Similarly with some herbs that I was given as a gift … one went into the herb garden straight away but the other is mint which will spread to take up all the space available and more besides. So my mint is currently in a pot, whilst I carefully consider an appropriate location. The mature size of a plant and its propensity to spread are definitely important issues to consider.

    • Ignore these considerations to your peril, and the endless problems from plants too closely spaced or too rampant. Do you put a saucer under the pot when you plant mint? Beware the runners sneaking out through the drainage holes! Thank you for these great tips, Peggy 😉

  2. Oh yes !! I know what it’s like !!! Now that I am old and smart (haha) I first look for the plant/tree/bush on the net to know all the details about the plant I want to buy 😀

  3. Oh. FG – this is one of the most important tips ever – size does matter – and I have had a butterfly bush too close to the house – and then an evergreen tree was split by snow one year and thank God because it was too gigantic for the spot we had it!
    And the title of the post is just fun – I also like the name of the green thumb challenge – I sometimes say some folks have a khaki (or army green) when they start finding their groove – 😉
    And how nice that you and your garden friends share plants and I have enjoyed getting. To know more of you.
    Lastly – the tip about the sucker plants that spread / is something I wish I would have known in 2008 – we out in blackberry bushes and they spread way too much. We are taking them all out – I have other issues with their Moldy dead stalks – but thankfully we never planted bamboo – our friend had septic tank probs from bamboo.
    Have a good week and ttys

    • Thanks Yvette 😊 Our gardening mistakes make for hilarious stories in retrospect , but oh the trouble and extra work they cause ! I once planted a Chinese Wisteria besides the deck of a wooden house ! Now that was a major blunder ! I was young and inexperienced and thinking only about the flowers . …Have a wonderful day and please be careful the rest of the week in this heat 🐢

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