Gardening in Larimer County

This summer we’ve all had a crash course in gardening in an arid climate. This season’s drought and heat have made many concerned Colorado gardeners learn more about low water gardening. Now, as our landscapes relax into the relatively carefree beauty of autumn, we have the chance to reflect on the lessons of this difficult season and to consider how we can make our yards more beautiful and more drought tolerant in the future.

By now, many of us can probably recite the seven principles of xeriscape in our sleep: Plan ahead, improve the soil, limit turf areas, select low water use plants, use mulches, water efficiently, and practice good maintenance.  It is time to look at our gardens with keener eyes and consider how we might better put these principles into action.

Late summer is prime time for sitting out in the garden and concocting plans. A gardener can spend a lovely evening sketching out a garden plan brimming with drought-tolerant plants. Walking around the yard, the gardener might also take notes on the existing garden and categorize plants by how much water they use.  After classifying the plants as low, moderate, or high water users, the more energetic gardener might even be inspired to grab a spade and do some transplanting.  Transplants should be grouped together by water need.  Generally, spring and summer flowering perennials can be transplanted after Labor Day while fall flowering perennials should be transplanted in early spring. However, the gardener should be careful to make sure that transplants will be able to get the water that they need in this dry year.

September is also a good time to assess how well plants are reacting to garden soil.  Many low water plants need well-drained soil.  Penstemons, lavender, sunrose or helianthemum nummularium are just a few of the drought-tolerant plants that demand well-drained soil for peak performance.  As many Colorado neighborhoods have clay soil which drains very slowly, the gardener should amend the soil with compost when planting a new bed.

When the drought breaks and watering restrictions are but a memory, it will be a good time to get rid of some of the thirsty turf.  It feels good to dig up unused lawn and concentrate on preserving those areas of turf, which serve a definite purpose.  If the lawn is free of weeds, the gardener can reap the benefits of tilling the lawn into the soil in fall, allowing the turf to break down over the winter, and planting in its rich compost in the spring.  If the lawn is weedy, the gardener might try disposing of the lawn by applying a glyphosate product in September and October.  The gardener must be careful to read the product’s label and to avoid spraying any desirable plants. Glyphosate will indiscriminately kill both the turf and the weeds without leaving a harmful residue in the soil. Come spring, the de-turfed area should be ready to plant with a variety of attractive, drought-tolerant plants. Of course, turf and weeds can be attacked with a hoe, but using this method, the gardener will probably have to devote more time to weeding in future seasons.

The most enjoyable part of creating a xeriscape garden is selecting low water use plants.  Late summer is a fantastic time to visit xeriscape gardens and make up a plant wish list.  In a month when some gardens are looking bedraggled, xeriscape gardens are dazzling.  Blue mist spirea (Caryopteris x clandonensis), trumpet vine (Campsis radicans), Russian sage (Perovskia atripliciafolia), Autumn Joy sedum (Sedum spectabile “Autumn Joy”) and heliopsis are just a few of the water-thrifty plants that are at their best in late summer.  If you’re tempted to purchase some drought-tolerant plants at the late season nursery sales, be sure to plant and water your new acquisitions promptly. Remember that even drought tolerant plants will need supplemental irrigation for one to two years until they get established so don’t plant unless you are certain of sufficient irrigation.

New and old plants also need to be mulched.  Proper use of mulch reduces water need, weed growth, and soil erosion. Mulch can also provide plants with added winter protection. Organic mulches like bark chips are the most commonly used mulches in our landscapes.  They improve the soil as they degrade but can also rob nitrogen from the soil as they break down.  Another option is an inorganic mulch like chipped stone.  Chipped stone or pea gravel should be less than 1/2 inch in diameter and of a medium color so that it neither reflects nor absorbs too much light. Inorganic mulches will not, however, add nutrients to the soil as they degrade.  Inorganic mulches have been known to improve drainage as they work into the soil, but inorganic mulches are difficult to get rid of and will earn the gardener curious looks from their neighbors until the landscape fills in.

Water use should be considered in every season.  In late summer, the gardener might choose to take advantage of the great weather and install a drip system or other efficient watering system.  Old sprinkler systems should be checked for coverage, and as fall approaches, the landscape should demand less water.  Certain drought tolerant plants like purple iceplant (Delosperma cooperi) will withstand the winter better if they are given no supplemental water after September 15.
 Maintenance seems to be the downfall of many xeriscape gardens.  Low water does not necessarily mean low maintenance.  Even if xeriscape gardens tend not to attract as many weeds as unmulched, heavily-watered gardens, there is still weeding to be done particularly since weeds can rob drought-tolerant plants of the bit of water they demand.  Also, certain xeriscape plants are prolific self-seeders.  Red orach (Atriplex hortensis ‘Rubra’), snow daisy (Tanacetum niveum), and Centranthus ruber are just a few of the low-water plants that should be deadheaded before they go too heavily to seed. Other plants like lavender should not be pruned too heavily after August.

Learning the lessons of this difficult, dry summer to heart might just make us all better gardeners.

Q: Could you suggest some good perennials to try to grow in dry shade?

A: The following plants are good choices for dry shade: Sweet woodruff (Galium Oderatum), a pretty groundcover with finely cut leaves and white flowers in spring that smell of vanilla; creeping grapeholly (Mahonia repens), an evergreen groundcover with yellow flowers in spring, blue berries in the fall and spiky foliage that goes from dusky green in the summer to a delightful burgundy in the winter; Hermann’s Pride dead nettle (Lamium galeobdolon) a small mounding plant with intensely patterned green and white foliage and yellow flowers, and Brunnera macrophylla a large leafed groundcover with tiny yet striking blue flowers in spring.

Q: I’ve got a kind of grassy weed in my lawn.  It has thick, blue blades, and when I pull it out the roots are long and bright white and seem to stretch on forever.  What could it be and how can I get rid of it?

A: The weed you describe might be quack grass or Elytriga repens.  Quack grass spreads by long, white rhizomes, and often, pulling the weed out of the lawn will only make the situation worse.  Any bit of rhizome that remains in the soil can take root.  To get rid of the weed in your lawn, let your grass grow a little bit longer between mowings, and you will be able to clearly see the clumps of quack grass sticking up above your lawn.  Very carefully, apply a glyphosate product to the clumps using an artist’s paintbrush or a bit of sponge attached to a dowel.  Avoid drips and spills as they can damage your lawn.  If you should spill some of the product on your lawn, flush the area with water.  Wait a few more days to mow your lawn.

Q. How do I stop my bronze fennel plant from sending up seedlings everywhere?

A: Allowing a few seedlings from a bronze fennel to grow could be a good thing as the plant is a favorite food of the larvae of swallowtail butterflies and sometimes the plant can be short-lived.  However, deadheading the plant after all flowering is finished and before most of the seeds mature is recommended.  Use caution when working with fennel because the plant juices can cause purple discoloration of the skin on some individuals.  This discoloration can last for months and is a result of phyto-photo dermatitis; a reaction brought on by sunlight combined with the plant juices.  It is best to deadhead the plants after sundown and wear gloves, a long-sleeved shirt, and pants.

Q: I need to move a peony, should I wait to do it in spring?

A: Fall is actually the best season to move peonies.  When transplanting be careful to situate the peony in a sunny location and make sure to plant it at the same depth that it has been growing in the ground.  Peonies often do not bloom if they are planted too deeply.

Because of Colorado’s dry air, low soil moisture content, fluctuating temperatures and drying winds, fall and winter watering is essential.  Plant roots can be injured or killed.  Plants whose roots have been injured may seem healthy and grow in the spring only to die in late spring or summer.  Water only when temperatures are above freezing early in the day so the water has time to be absorbed into the soil before the nighttime freeze.  Be sure to unhook your hose after watering.

Protect young trees from sunscald in the winter.  Damage is usually found on the south and west sides of the tree.  It is caused by moisture loss and daytime temperature fluctuations.  Use crepe tree wrap for the first several years on thin barked trees.  Overlap it as you wrap the trunk from the bottom to the top.  Secure it at the top to keep it from coming off in strong winds.  Be sure to remove the wrap in spring.

Fall is the time to dig up begonias, gladiolas and dahlias for winter storage.  For dahlias, wait two weeks after the stalks have been killed by frost before removing them from the ground and make sure that you don’t damage the roots.  Shake the soil off and store in sawdust in a cool, dry place.  With gladiolas, wait until the tops die down before you dig.  Remove the top and any withered portions of the corm before storing in a cool place with a little higher humidity.  Begonias should be dug up after frost and stored in sawdust in a frost-free area.

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

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This page updated:  March 28, 2003