September 27, 2019

Helpful Garden Tips - Maintenance of Perennials

Mary's Greenhouse
As most of you know, I own a small greenhouse business, Mimi's greenhouse. I buy most of the plants that I don't grow myself at Mary's Greenhouse in McMinnville, Tn.  This article was on their website and I thought I would share it here.

(*Disclaimer: Mary’s is a greenhouse grower of plants and we don’t currently offer landscape services. Greenhouse production is different than outside gardening.  For professional advice, please consult a landscaper or full-service garden center.)

What is the difference in pruning and deadheading?  Pruning usually applies to more woody type plants and accomplishes several things such as shaping, rejuvenation and sustained health. There is more than 1 kind of pruning. General pruning can be used to re-shape the plant(s) and to rejuvenate established plants by removing old stems and stimulating new growth.  Hard pruning usually refers to cutting them way back, sometimes several inches from the ground. Care should be taken in cutting plants this far back. Some research should be done on how and when to do this. Deadheading is cutting back the spent bloom stems. Deadheading can promote rebloom in many plants. It is best that you remove all the debris from around the plant when you cut them back to help with any disease. Although deadheading is important, there are lots of plants that do fine without it.

When is the best time to cut back perennials? Lots of plants can benefit from being cut back immediately after blooming. This can make for a neater and stronger plant. Cutting back can encourage re-bloom in several perennials. Consider applying a slow release fertilizer when you cut them back to help replace their energy stores. To promote good health and help with insects, remove all the debris from your beds.

When and how do I cut back peonies? We recommend that you wait until fall – or just let them die back naturally. The spent blooms can be removed, but it is best to leave the rest of the plant. They are sometimes unattractive in the garden after blooming but the plants need to replenish their energy reserves for the next year.  Peonies can be cut down to the ground as new growth emerges each year. After frost, the dead foliage should be removed to help promote good health.

When do I cut back and/or divide daylilies? Daylilies can be cut back to the ground after blooming.  New growth will emerge and make for a neater plant. If you are going to divide them, it is best to do so after blooming. Consider applying a slow release fertilizer after blooming; this will help them replenish their energy stores for the next bloom cycle.

When do I divide iris? German iris (bearded iris) seem to do best if divided in the late summer to early fall.

When and how do I prune buddlejas?  Buddleias can be pruned in early spring.  If your plants are already leafed out, they can still be pruned; it will just delay the blooms. Most benefit from a hard pruning as buddlejas bloom on new growth. Pruning rejuvenates the plants and usually increases number and size of blooms. Some varieties can get quite large and can be cut back to 12-24”. Deadheading through the summer may extend your bloom time.

When is the best time to divide perennials? As a general rule, perennials do best if divided in the spring or fall as it is usually less stressful on the plant. The spring and the fall are usually milder months and the plants have time to re-establish themselves before summer or winter. It is also best not to divide right before blooming or during the blooming season. Plants can be divided after blooming when you are cutting them back – just be sure to provide ample water should it be hot and dry.


When and how do I cut back hydrangeas? This is not a simple answer because there are different hydrangeas and they have different pruning needs. You need to determine if your plant blooms on old or new wood.  ‘Old wood’ means stems from the previous years’ growth and ‘new wood’ means this years’ growth.  There are lots of new hydrangeas coming to market every year so there are exceptions but here are 2 general guidelines to follow for established plants.

 1) Oakleaf, most mopheads and lace caps (macrophyllas) typically do best if pruned right after flowering and then left alone except for culling dead limbs, etc. as they bloom on old wood.  They start forming the next year’s blooms in the late summer/early fall. Pruning helps rejuvenate established plants and you can remove about 1/3 of the stem lengths. Pruning every year isn’t necessary in most cases. You can deadhead spent blooms through the blooming season.

2) Other species such as arborescens (Annabelle and similar) and paniculata types (Limelight or Little Lime, etc.) bloom on new wood and can benefit from a pruning once a year. Pruning these varieties helps strengthen the stems and produce bigger flowers.  A typical pruning can be done in the winter months and removes up to 1/3 to 1/2 of the old growth.  These types can be pruned back to about 12” above the ground if needed after our killing frosts. Pruning can also be done immediately following blooming. Some varieties will re-bloom if deadheaded during the growing season.

Consideration should be taken when planting hydrangeas. Allow them plenty of room to grow. Many varieties, especially the older ones, can get large. If they have ample room to grow, pruning is not as big of an issue.

How do I prune my roses? The correct pruning techniques depend on the type of roses you have. Here are 2 general guidelines to use as a reference bearing in mind they may need to be modified a bit depending on variety, age of plant and other factors.

1) Most hybrid teas, grandifloras, floribundas, some climbers, and some shrub roses (like Knock Out) bloom more than once and can be pruned the same way.  Typically, these types of roses bloom for a time and then rest before re-blooming. Plants can be shaped up in early spring (mid-February to March) and then can be deadheaded through the growing season. Cutting the spent flowers encourages re-bloom in many varieties.  The first pruning in early spring should remove all the dead and weak canes, any suckers coming up from the root stock and about 1/2 of the plant’s height. To promote good health, be sure to remove all debris. Tidiness also seems to help with rose rosette.

2) Some climbers and heirloom roses bloom only once a year. It is best to cut back immediately after blooming so that you don’t cut off next year’s blooms. These roses can start forming the next year’s blooms in late summer and fall. All dead or weak canes should be removed. Old flowering canes should be removed as needed to make room for the new shoots coming up.

Additional online information: Buddlejas – gardenseeker.com Roses- www.clemson.edu/extension/hgic/plants/landscape/flowers/hgic1173.html; https://extension.illinois.edu/roses/prune.cfm Hydrangeas – hydrangeashydrangeas.com, ucanr.edu/datastoreFiles/268-86.pdf, www.provenwinners.com 

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