Hold That Water!
Patsy Cunningham


Roses love water… a couple of inches each week we’re told. For a large rose garden, this is neither cheap nor easy to do. Most of us already try to retain soil moisture and reduce watering needs by adding organic material to the soil and mulching our gardens. We cheer when we get a good soaking rain that saves us a couple of hours of hand watering and an increased water bill. However much of that soaking rain drains right through our soil, out of reach of the needy roots. Much of Rhode Island has a sandy loam soil, ideal for drainage, not retention. Wouldn’t it be nice to hang onto more of that bounty of rain? A thoroughly modern product makes that possible: potassium salt based acrylic polyacrylamide polymers.

Sounds just like what you’d like to add to your soil, huh? Believe it or not, that very synthetic product breaks down in your soil to simple carbon dioxide, nitrogen (in ammonia form) and water, not the plastic you’d expect. Polyacrylamide is sold under many different names: SoilMoist, water crystals, Terra-Sorb, Hydrosource, Water Reserve, Water Keep, Hydro-mulch, PAM, copolymer, Aquasorb, Agrosoke, Smart Soil, Aquacrystal, Bioplex, and Agro-diamonds. For the most part, it looks like large salt crystals when it’s dry. Add enough water though and it quickly swells to a soft Jello-like mass. This gel absorbs extra water in the soil before it drains away. As the soil dries, the polymer slowly releases water back into the soil. This helps you two ways: initially by preventing an area from becoming waterlogged and then by keeping the soil moist for a longer time. Though figures vary, these polymers can hold about 200 times their weight in water; more if the water is mineral free and less if it contains water soluble fertilizer or other minerals. Since the polymer captures some of the water that would be lost to drainage or to a lesser extent evaporation, watering can be reduced by up to 50%.

Polymer hydrogel crystals can be added directly into your planting hole, mixed well with the soil below and to the side of your roses. They should not be present in the top 2” of soil. Also do not just pour the crystals en masse into the bottom of your planting hole. It is not unknown to have a plant literally pushed out of the ground by the expanded mass of gel when planted this way. The crystals are particularly useful in situations where roots are likely to dry out too quickly. In my experience, this includes own-root miniature roses. Minis have a more shallow root system than their full sized brethren. The ones we have planted along a hot south facing walkway were drying out far too quickly and were not thriving. I started using SoilMoist, the polymer most readily available locally, and have seen a definite improvement in the strength of the plants and the quantity of blooms. The manufacturer recommends one and a half to two ounces of the polymer per foot of rootball for shrubs like roses. In a bed, a pound per 100 square feet is recommended, but since this stuff is not cheap, I stick to using it directly in the planting hole. Rosarians who grow roses in containers know that the pots require frequent, often daily, watering. This is an ideal place to start with these polymers. Use 1 ounce to amend the soil in a 5 gallon pot. Make sure you fully “charge” the crystals by watering heavily after planting. Maintain your regular watering schedule for the first week, then reduce your watering frequency. The crystals may also be introduced to the soil mixture pre-charged, that is, fully hydrated. “At Rosemania, we recommend adding this product to all newly planted roses and other plants. We like to pre-hydrate our crystals before putting them into the soil. Simply add 8 oz (1 cup) to three gallons of water and allow them to hydrate over night. The next day you can mix 2 cups of hydrated crystals in the soil you use for each potted plant and up to 3 cups of hydrated crystals for plants in the ground.” Some sources recommend pre-moistening with a water soluble fertilizer mix. The crystals can retain and then release the dilute fertilizer as needed.

There are a number of other advantages to using these moisture retaining hydrogels. They are basically pH neutral and certified non-toxic. Since they repeatedly expand when wet and contract when dry, they help reduce soil compaction, providing more aeration to the roots. The polymer cannot be absorbed by the plants, but the roots are attracted to these moisture zones, often growing right through the crystal to take advantage of the water pocket. Less fertilizer is also lost to run-off and percolation, saving on fertilizers and reducing water table contamination. During drought times with water restrictions, it can allow your plants to continue to grow stress free between waterings. The crystals can swell and shrink up to thousands of times. They last at least two or three seasons, and have been found to be effective up to 10 years. For roses that are already in the ground or in pots, the dried crystals can be added by poking pencil sized holes in the ground around the plant and adding the recommended amount divided up between the holes. I first became interested in these crystals when another rosarian, Audrey Osborn of the Lower Cape Rose Society, mentioned using cheap disposable diapers when planting her minis. Since the crystals in the diaper absorb water, she figured it would be helpful, and at that time it was cheaper than the commercial products. it turns out that diapers use a similar polymer called polyacrylate instead of polyacrylamide. it’s great for holding water but rapidly breaks down, unlike the products made specifically for soil. These hydrogels have some other specialized uses. A finely ground version is used as a seed coating.. It’s mixed with graphite as a lubricant to keep the seeds from sticking together. The ground polymer provides a self contained reservoir for each seed, increasing germination. The finely ground version is also used to protect bareroot plants from dehydration. They are dipped when wet into the fine powder or dipped in a slurry made from the polymer and water. The hydrated gel can be used for soil-less propagating; providing moisture, air and a supporting medium to cuttings taken for rooting. You can even use the gel for displaying cut flowers, as it keeps them in place almost like the oasis used by arrangers and provides plenty of water. Food coloring can be used to color the gel for this, which sounds kind of tacky, but could work in some arrangements. A particularly compelling use was for constructing high yield weed-free gardens in low rainfall non-tillable land with no digging equipment. The Hydrosource granules were spread on a plot of land without removing its weeds, grass or rocks. A heavy weed barrier called a Sunbelt was tacked over the plot. Small slits made in the fabric and holes punched into the ground to accommodate the young food plants. Watering was minimal but good results were achieved. While we may not have the need to do this, starting a weed-free garden without removing the sod is at least intriguing. The polymers are also known for reducing or eliminating transplant shock, particularly if the hydrated granules are present within the root ball at the time of transplanting. The polymers also come in special forms premixed with fertilizers and even with mycorrhizae bacteria, (but that’s a different interesting topic).

As you can imagine, prices vary widely depending on the brand, the amount purchased and the source. Local nurseries carry small bags of it, enough to get you started with some pots or minis. So when you buy those little minis next year and pot them up temporarily until they’re big enough for the garden, add some polymer hydrogel crystals to your potting soil and see if it affects your success rate. Larger amounts can be ordered on-line and can even be found on E-bay. Next year, I intend to mix it into soil mix for germinating seeds as recommended by rosarian Henry Kuska. I also figure on trying it more widely next year by adding it to the soil around some roses that the hose just doesn’t easily reach.

(reprinted from the August 05 Rhode Island Rose Review)




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Date last edited: 01/21/10
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