Water-Absorbent Polymers

Some notes about water-absorbent polymers used in container mixes in North America--are they yea or nay for growing veggies; and taking another look at the most compact of fruit trees.
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

May 17, 2009

Above, a collection of ‘Maypole’ crabapple trees at the 1990 Chelsea Flower Show (the collection is known as ‘Colonnade’ in North America, but in England they are known as ‘Ballerina’. Below, a delightful Sweet Violet (Viola labradorica) growing beside our small pond is at its best right now; and alongside is the reddest of Anenome pulsatilla, the cultivar ‘Red Clock’. The plant is now correctly known as Pulsatilla vulgaris ‘Red Clock’. Author photos.

Just this past Friday Christine Allard wrote to Donna Dawson with the following comment and a question on Pro-Mix Container Mix. Here is what she said: “It's still cool & freezing overnight here in Lethbridge so I'm dragging my patio pots in & out daily ... hope to be able to at least leave out my lettuce boxes overnight soon! I've been reading conflicting advice with regard to using potting soil that has water-retaining crystals in it. Seems to be OK for ornamentals, but NOT to be used for anything edible. Can you please advise why? Unfortunately I potted everything for my deck in this kind of potting mix, and now I'm concerned that my strawberries, tomatoes, lettuce, herbs, etc. may be contaminated in some way. I did mix the bagged mixture with some composted steer manure and triple mix of peat, compost and humus, so it's not 100% the original Pro-Mix for containers.”

You’ve asked an interesting question Christine. The entire topic of water-absorbent polymers or water-holding crystals (that, in theory, hold extra water and reduce watering frequency) is intriguing. And, it definitely depends on in what country you purchase these. I recall using the first ‘batch’ of a container mix made by one of the largest manufacturers of these container mixes, a way back in the late 80s. I went to a lot of trouble to remove the previous good quality potting soil I had in about 30 running feet of suspended containers, most of them on the second floor. I recall a friend who helped, saying, “this better be good stuff, what a lot of work this is!” Well, it was NOT!

In fact, with the new ‘stuff’ in the boxes, they required more frequent watering than they did the previous year with a good mix that had no water-absorbent polymer at all. That experience caused me, a few years later when I was horticultural editor of Plant & Garden magazine, to institute a major testing of all the various container mixes on the market at that time. Horticulturist Ken Brown carried out the test for us and came up with surprising results, not unlike what I had encountered a few years earlier.

With so many years past, and many advances in container-mix formulations, none of that research would be applicable now. But it does point out the need to be wary of just what we are using, and perhaps run our own tests between two differing products under each gardener’s own conditions.

I hinted at differing products in different countries. My good friend Graham Ross of Sidney Australia, back in the 90s, I believe, experimented with a number of these products manufactured by different companies in Australia and New Zealand. I remember him telling me that one specific product made in New Zealand was absolutely the best in reducing the watering schedule for the plants growing in it. Now, in Australia and New Zealand they actually use these crystals extensively as additives to garden soils, rather than just for container plantings as we do.

He told me, as I recall now, that the one NZ product allowed gardeners to grow both flowers and vegetables in soil mixed with the polymer--and that the more common products used more extensively in his country were not recommended for use with vegetables.

So, my point is, obviously these polymer products are made with varying ingredients, and apparently some are not suited to growing vegetables due to their chemical content possibly affecting the vegetables negatively; i.e. the chemical may be taken up in the vegetable making it unfit for human consumption.

But not all of the polymers are subject to the “no vegetables” rule. I know not what the Premier Horticulture people are using for a polymer now, but I do note that in much of their literature they specifically mention vegetables as crops that can be grown in it. So, you may not have a problem at all if that is the product you used specifically. I suggest you send them an e-mail message, through their Website:  or call them on their toll-free line: 1 800 667-5366 if you wish their verification.

The next question goes back a week ago; I’ve already replied but thought my comments might be of interest to other gardeners. The question came from Norm Dagenais and went like this: “I have just received two columnar apple trees but there were no planting instructions. I searched the internet for planting instructions but there is contradictory ad-vice [ooh, unusual, eh!]... one suggested planting the bud union two to three inches below the soil line, yet another suggested the bud union should be just above the soil line. This is my first attempt at columnar apples, can you ad-vise me as to the correct planting procedures. I have the roots of the trees in water for now but don't know how long I can leave them that way. Thank you.”

That request caused me to write back as follows: “Please, please do tell me your location when asking questions that may involve hardiness. Also, in this case, can you tell me just what trees you have? There are various different types of these columnar trees now; did they come with any tag at all, or did the nursery tell you anything more about them. Regarding how you are keeping them, I would not keep them in just water for more than ten hours. They should be in wet sphagnum or peat moss, or Coir, or in a heavy mix of clay and water. The roots do require oxygen as well as water. Thanks.”

Norm responded immediately as follows: “Thank you so much for your prompt reply. I live in Mississauga, Ontario and ordered the columnar apple trees from Dominion Seedhouse. They have been very reliable in the past but on this occasion they did not provide specific planting instructions ... actually this may have been the first year they offered columnar apple trees as I can't say I noticed them in previous catalogues. I purchased the Malus pumila ‘Scarletspire’ and the Malus pumila ‘Crimsonspire’ trees. I hope they deliver the results promised. For many years I listened to you and John Bradshaw on CFRB and indeed telephoned in to you for advice on a couple of programs. I must say I do miss hearing you on radio. Thanks.”

My short answer to Norm was: “Attached is an article on the columnar apple trees I wrote in 1996 when they were newly available in Canada. They should be planted at the same depth as they were in the nursery, and as with all nursery stock, you should be able to see a slight colour difference on the bark that indicates where the soil line was. That will likely mean the graft will be above ground. There should be no need to protect them in Mississauga over the winter.”

Here too, is an excerpt from the article I wrote in 1996: “There have been dwarf apple trees, mainly coming from East Malling in England, for at least four decades that I remember. But the Colonnade Collection is different! They are the smallest in both height and diameter that anyone in the dwarf apple industry has seen, according to at least one long-time apple tree nursery owner in British Columbia to whom I have talked on a couple of occasions.

“How small?

“Their growth habit is a perfect cylinder or column shape, of only 50 cm (20") or less. The height may eventually reach two metres, but will be easily maintained at 1.5 to 1.75 m, or 5 to 6 feet. There are three apple cul¬tivars, and one crabapple. It is the latter that I first saw at the Chelsea Flower Show in London, England in May 1990. In fact, the trees were introduced at that show just a year earlier. The crabapple, ‘Maypole’ was very dramatic in full bloom with spectacular carmine red flowers. It also has large (5 cm /2") purple-red fruit in Autumn which can be used for jelly-making.

The four trees are collectively known as the Colonnade Collection in North America, but were introduced in England as the Ballerina Series.

“The three eating apple cultivars now available are: ‘EmeraldSpire’, an early variety with pinkish white flowers followed by mid-September-ripening green apples with a golden blush; ‘UltraSpire’, has similar flowers but these are followed by red fruit that have a yellow/green blush, and are produced in late September; and ‘ScarletSpire’ also with similar flowers, followed by large red fruit somewhat like Red Delicious, in early October.”

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