By Prof. Dr. Willem VAN COTTHEM

University of Ghent, Belgium


People are asking me why I am in favour of drilling drainage holes in the sidewall of a container.  Why are those in the bottom not good enough ?

Of course, the classic drainage holes in the bottom are functional. Rain or irrigation water is running through the potting soil towards the bottom.  A possible surplus of water is thus easily evacuated through that single hole or the different holes in the bottom.

However, potting soil contains a high number of bigger and smaller cavities, that are filled with air.  When watering a container (pot, bottle, bucket, barrel, etc.), irrigation water is running rather swiftly towards the bottom of the container.  A number of those cavities are thereby filled with water and air is pushed out.  That is visible e.g. when we immerse a pot in a bucket of water: we see the bubbles leaving the potting soil during a short period, until influent water has pushed out most of the air of the bigger cavities. Even if we do not see bubbles leaving the soil anymore, a certain volume of air is still remaining in the potting soil, namely that in the smallest cavities.

This means that, when watering a container with the classic drainage hole(s) in the bottom, water will run quickly through the potting soil, moistening that soil for its major part, but not completely.  A lot of precious water will run out of the container through the drainage hole(s) in the bottom and be lost for moistening of our plants. This means that a number of cavities will still be filled with air (leaving those small parts of the potting soil dry).

Now, imagine what will happen if we put the container (with holes in the bottom) in a recipient, e.g. a bowl.  Water running out of the drainage hole(s) is then collected in the bowl.  From there it will gradually be re-absorbed by the potting soil (and the rootball).  It re-enters our container and after a certain time it moistens the potting soil almost completely.  However, if we exaggerated when watering, too much water will be collected in the bowl and that water will stand there for a longer time, having a negative effect on the roots (e.g. by asphyxiation).

On the contrary, if we did not exaggerate when watering, only a smaller quantity of water will be collected in the bowl, and that quantity will rather quickly re-enter the container, completing the moistening of the potting soil and the rootball.

Considering this phenomenon, it came to my mind that drilling drainage holes in the sidewall should have the same effect as collecting a quantity of irrigation water in that bowl.  My experiments proved the positive effect.

2009-12-30-bottle-preparation-p1030170  2009-12-30-bottle-preparation-p1030171 

Photos WVC: 2009-12-30 BOTTLE PREPARATION P1030170.jpg and 2009-12-30 BOTTLE PREPARATION P1030171.jpg

In a first series of experiments I drilled 2 opposite holes (diameter 0,5 cm) in the sidewall of plastic bottles at 2,5 cm above the bottom.  I preferred to get 2 opposite holes, expecting that one of the holes could be clogged.  Somewhat exaggerating the watering, I noticed that a lot of water was running out of the 2 drainage holes.  Nevertheless, the quantity of water kept in the bottom of the bottle was readily moistening the potting soil above, having a positive effect on the growth of the plant in it.  None of the holes was clogged in a first period, but I expected that it could happen when the growing roots would reach the bottom of the bottle.

p1030643  2010-03-29-avocado-p1030768


Photos WVC: 2010-03-03 BOTTLE PREPARATION (P1030641-P103064 / 2010-03-29 AVOCADO P1030768.jpg and 2010-03-29 AVOCADO P1030765.jpg

Therefore, I have set up a second series of experiments with 2 opposite drainage holes, having a diameter of 1 cm (reducing the risk of clogging).

A third and fourth series of experiments were set up with 2 drainage holes (diameter 1 cm) in the sidewall but respectively at a height of 5,0 cm and 7,5 cm above the bottom.


Finally, I used bigger containers with bigger holes (3 cm) at different height.

My general conclusion of these experiments is that drainage holes in the sidewall of a container are better than the ones in the bottom, because:

(1) one is saving a lot of water (less loss);

(2) one is saving also a quantity of fertilizer (otherwise lost by leaching);

(3) one registers better plant growth.

It is obvious that there is a close relationship between the dimension of the container (and thus the volume of the potting soil) and the height of the drainage hole(s) above the bottom.  The higher the holes in the sidewall in small containers, the bigger the risk of asphyxiation and root rot.  One should also determine the optimal diameter of the drainage holes.

Today, I hope that researchers or students will set up scientific studies to determine the optimal method to improve plant growth in containers by taking into account the position and dimension of drainage holes in the sidewall.

Anyway, container gardeners using planters without any drainage holes are hereby recommended to drill those holes not in the bottom, but in the sidewall.

Caring for mandevilla, bougainvillea


Photo credit: Google

The bushy, vigorous habit of Sun Parasol Pretty Pink mandevilla tropical vine makes it ideal for growing in containers.

CAROL LINK: How to care for mandevilla, bougainvillea

Each spring, Oscar situates a large container filled with a beautiful, pink-flowering mandevilla vine along the driveway near the side entrance to our home. Years ago, I placed a 3-foot, lightweight metal trellis in the container. With a small amount of assistance from me, the vine climbs the trellis throughout the spring and summer. Occasionally, I pick up a stray tendril and wind the vine through the trellis. Throughout the growing season, the beautiful vine decorates our landscape and hummingbirds zoom in, butterflies flutter in and bees buzz in to enjoy the lovely pink flowers.

Mandevilla vines are sensitive to the cold, so in this area, all mandevilla plants should be brought inside and stored for the winter. Because our personal mandevilla plant grows in a large container, Oscar recently used a set of hand trucks to roll the container into the garage for the winter. I will apply a small amount of water to the container about once each month until spring. That’s all that’s necessary, because the plant will soon be going dormant, and applying too much water during the winter could cause root rot.

Next spring, after the last predicted frost, we will move the container back outside, situate the plant in full sun, cut the vine back to about 1 foot in length, apply fertilizer and then keep the plant watered well. Once again, the plant will grow rapidly and very soon the vine will be climbing the trellis, and in due time, beautiful pink blossoms will once again dangle from the vine.

This is a terracotta pot holding a bougainvillea – http://www.texasmornings.com/wp-content/uploads/2012/07/bougainvillea-on-fence.jpg

A bougainvillea vine is treated in much the same manner as a mandevilla.


Read the full story: Houmatoday

Kale, mustard and collards



On Gardening: The brassicas are taking center stage along with kale, mustard, and collards too

By Norman Winter

Tribune News Service

The brassicas are taking center stage!

In the fall and winter season, we have always dabbled in flowering kale and cabbage, but it seems in the last couple of years things are changing. The cruciferous crops are doing their part to create the WOW factor in flower beds across Georgia. It’s not just flowering kale and cabbage but edibles like the Toscano kale and would you believe that old southern favorite collards.

Last year, anyone who went to the Savannah/Hilton Head International Airport could not help but notice the monolithic blue-green leaves not only serving as the backdrop to the pansies and snapdragons, but the enormity of the leaves created their own photo-worthy moment. This year, I am seeing collards used elegantly in mixed containers and even baskets. Why not? You couldn’t ask for a better companion to the colorful pansies. When I took the photo I was thinking now I need catfish and cornbread.

While collards are really old fashioned, the application with ornamentals is new and trendy, at least in several generations. Toscano kale also called Toscana, Tuscan, Lacinato and Dinosaur kale is similar. Culinary experts know it is among the most flavorful and treasured in Italian soups and stews but recently new to the flower garden. So you can rejoice for incredible beauty and texture, but if you fancy yourself a chef, then the edible landscape is close at hand.

Read the full story: St. Augustine

Container gardens on rooftops and fire escapes, community gardens in vacant lots or on land in public spaces



Victory gardens a growing trend again

Over the past decade, gardening developed into a viable part of the news, as the ranks of home gardeners swelled to record highs. This growing interest in the growing season can be attributed to a stubborn continuation of economic concerns and an accelerating passion for anything green. “Going green,” whether in energy efficiency, environmental protection or food production, continues to enjoy a popular ranking as an “in” thing to do right now. It’s estimated that during the past decade several million new household gardens have been planned, planted, and tended by first-time gardening families in the U.S. Though this may be a new experience for many, in some ways it’s a repeat of an earlier effort made 75 years ago, when a financial depression and a world war brought many Americans ‘back to the land’ in the form of backyard plots called Victory Gardens.

In 1943 more than 20 million gardens were planted to provide fresh fruits and vegetables on the home front. During World War II much of the commercially produced food was used to feed the troops. In the face of shortages and rationing, Americans turned lawns and flower beds into garden plots. City dwellers were able to get into the act by planting container gardens on rooftops and fire escapes. Community gardens were developed in vacant lots or on land in public spaces. Some of the biggest public gardens were located in New York’s Central Park, San Francisco’s Golden Gate Park, and across the pond in Hyde Park in London. Actually, the Brits were the first to start growing their own food in 1940. As the war escalated, the movement spread throughout Canada and the U.S., as ordinary citizens did their part to support the war effort.

 Read the full article: The Hutchinson News

Make Acalypha yours


Photo credit: Gardendrum

With adequate food and water Acalypha ‘Macrophylla’ is outstanding

Fijian fire plant – how to grow Acalypha and its many cultivars

Arno King

Grow your own mint indoors



Growing Mint Indoors & How To Care It

Fragrant, fast-growing, and one of the most used culinary herbs– Mint can be grown indoors. Growing mint indoors is easy and doesn’t require many efforts!

Herbs can be grown indoors and mint is one of them. However, mint (or any other herb) growing indoors can’t grow as vigorously as outdoors. Still, you can enjoy those freshly picked leaves year-round, even in winters!

Read the full story: Balcony Garden Web

How to repot plants



Photo credit: Bedford-Sackville Observer

Learn how to repot plants the right way

Enthusiast? Enjoy foliage inside of your home as well



People enjoy plants both inside and outside of their homes. Container gardening, which is a planting method in which flowers and other plants are grown in pots and other containers, is quite popular because of design versatility. Containers can be moved from location to location if plants are not thriving in a particular spot. They also make gardening possible when there isn’t any available land space, which might be the case for apartment-dwellers.

Flower pots enable plant enthusiasts to enjoy foliage inside of the home as well. Houseplants can add beauty to interior spaces and help filter indoor air. House plants have been shown to purify indoor air.

Several plants are particularly good at filtering out common volatile organic compounds (VOCs). Having plants around can create inviting spaces and improve healthy conditions inside and out.

Part of caring for plants in containers involves knowing when a potted plant might need a little tender loving care. As plants grow larger, they may outgrow their containers and require more roomy quarters. Without ample space, plants may not be able to adequately draw up water and nutrients to support top growth. Repotting may seem like it is easy, but it actually takes a little finesse so not to damage the plants.

Gardening experts like those from Fine Gardening, HGTV and Today’s Homeowner suggest these repotting tips:

Read the full article: Bedford-Sackville Observer