Is it cold yet? The first half of December is typically fairly mild, but the cold weather can hit hard the second half of the month. Any frost sensitive plants in containers should have been brought in under cover of a patio by now. Be sure to apply frost protection to plants that are cold tender if a freeze warning is forecasted. Use a fabric such as N-Sulate, burlap or old sheets; never use plastic as it causes plants to burn where they come into contact with it. See our Desert Gardening Guide on Prevention and Care of Freeze Damage for more information.
Aloe plants will continue to bloom this month. Look for blooming:
- Firecracker Penstemon (Penstemon eatonii),
- Chuparosa (Justicia californica),
- Desert Marigold (Baileya multiradiata),
- Shrubby Bulbine (Bulbine frutescens),
- Paperflower (Psilostrophe cooperi),
- Cascalote (Caesalpinia cacalaco),
- Mount Lemmon Marigold (Tagetes lemmonii) and
- Jojoba (Simmondsia chinensis).
Ice plants will be actively growing as well as plants such as Kalanchoe, Dudleya, Cotyledon, Echeveria and succulent geraniums (Pelargonium).
If you must put holiday lights on your plants and trees, take care to wrap them loosely and remember to remove them after the holiday season. Don’t put “costumes” on saguaros or other columnar cacti, as this inhibits the plants ability to photosynthesize. However, lights on frost sensitive cacti and succulents can add a few degrees of protection during the cold winter months.
Chihuahuan Desert yuccas such as Faxon Yucca (Yucca faxoniana) and Beaked Yucca (Yucca rostrata) can rot easily when it is wet and cold. Plant them in well-draining soil and if they are on a drip system, make sure the system is turned off. Yuccas from the Mohave Desert are actively growing at this time such as the Joshua Tree (Yucca brevifolia) and Mohave Yucca (Yucca schidigera).
If winter rains have occurred, you probably have some weeds already. Keep up with the weeding so spring doesn’t catch you off guard. Weeds that you may encounter in your garden at this time include:
- Cheeseweed (Malva parviflora),
- Filaree (Erodium cicutarium),
- many Mustards (Brassica spp.),
- Prickly Lettuce (Lactuca serriola),
- Mediterranean and/or Arabian Grass (Schismus spp.),
- Bur Clover (Medicago spp.),
- London Rocket (Sisymbrium irio),
- Red Brome (Bromus rubens),
- Hoary Bowlesia (Bowlesia incana) and
- Sowthistle (Sonchus spp.).
For detailed information on weeds of Arizona visit An Illustrated Guide to Arizona Weeds by The University of Arizona Press.
Container plants that are winter dormant should be watered once a month or less. Winter growers in containers can be watered once a week depending on the weather conditions. Irrigation timer should be off at this time. Give your landscape plants a deep watering at least once during the month of December. Annuals, herbaceous perennials, vines, and groundcovers should be watered to a depth of 1 foot. Water shrubs to a depth of 2 feet and trees will need to be watered to a depth of 3 feet. Wildflower seedlings need to be watered once every two weeks or at the very least once a month if rainfall has not occurred. Water herb and vegetable plants as needed to a depth of 8 to 12 inches.
Continue planting succulent winter growers such as ice plants, Kalanchoe and Dudleya. Native plants that can be transplanted at this time include:
- Globemallow (Sphaeralcea ambigua),
- Penstemons (Penstemon spp.),
- Brittlebush (Encelia farinosa),
- Blackfoot-daisy (Melampodium leucanthum),
- Fragrant Evening Primrose (Oenothera caespitosa), and
- Desert Marigold (Baileya multiradiata).
Herbs to transplant include:
Herb seeds to sow include:
Vegetables to transplant include:
Vegetable seeds to sow include:
Continue pruning deciduous trees such as Desert-willow (Chilopsis linearis), Cat-claw Acacia (Senegalia greggii syn. Acacia greggii), and Chaste Tree (Vitex agnus-castus). Do not prune Mesquites (Prosopis spp.) or Palo Verdes (Parkinsonia spp.). Resist the urge to prune any damage on plants due to frost and do not prune cold-tender plants, wait until springtime. Many agaves are semi-dormant at this time and old, dead leaves can be removed by gently pulling from the base. Resist the urge to pull out the dead leaves that are firmly attached as this can damage the base of the agave.
Container and landscape plants will not need to be fertilized until spring. Continue to fertilize your winter vegetable plants if necessary.
Aphids may be on your winter vegetables and herbs. Before spraying aphids off with water or insecticidal soap, check to make sure there aren’t any beneficial insects presently working.