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All day at local nurseries, the questions come every few minutes; “Why are my aeoniums shriveling?

What can I do to keep my sweet peas blooming? Where did all the native plant inventory go? Why are my freesias and daffodils drying up?”

This time of year in Southern California, gardeners are seeing a lot of changes in their plants, and local homeowners continue to be baffled by what they see.

Probably the most important, yet poorly understood aspect of garden plants is the distinction between cool-season and warm-season plants. If I ever write a book about local gardening, this topic will likely be dealt with in the first paragraph, especially since it is so poorly presented by most authors. It amazes me how many gardeners still don’t understand that plants, almost all plants, can be divided into two groups, cool-season plants and warm-season plants.

When a gardener fully comprehends this cool season-warm season concept their world will change. A knowledge of the seasonal scheme of the individual plants in their gardens will alter their entire approach to gardening. It will open your eyes, like the day they tasted their first ice cream or learned to swim in the deep end of the pool. This discovery will be an “Ah-Ha” moment for many gardeners, a moment of tremendous relief, satisfaction and understanding.

Plants have seasons, all plants – even plants in southern California. In fact, especially plants in southern California.

Plants grow, flower and thrive during their pre-determined preferred season. Generally, this is either in the cool half of the year or in the warm half of the year. During a plants non-preferred time of the year it retracts in one way or another, sometimes in obvious ways but often in subtle ways, not noticed by casual gardeners. This off-season usually results in the plant stopping or slowing downs its growth, dropping its leaves, contracting its roots or generally just sulking. Of course, a gardener’s wishes and desires won’t change a plants preference for either a cool or warm season in the slightest.

Cool_Season_Plants6-26-10

Unfortunately, plants can’t talk and they don’t come with labels that say “cool-season” or “warm-season”. I wish they did, but a warm-season plant in Seattle might be a cool-season plant in Orange County. They may even be different in Riverside than in Newport Beach. Plant tags couldn’t possibly keep up with all the nuances of regionality, nor can books, websites or other references that deal with more than very local areas.

Perhaps the easiest illustration of cool-season and warm-season plants is in our lawns. Bermudagrass andSt. Augustine grass love the summer, but hate the winter. They’re warm-season plants. Conversely, fescue, bluegrass and ryegrass are cool-season grasses, enjoying the winter but suffering through the summer. Once a plants seasonal preference is understood and embraced by the gardener they know that planting bermudagrass in November is a pretty silly endeavor, just as impractical as broadcasting fescue seed in summer. Therefore, bermudagrass gets fertilized in the summer, fescue in the winter. Homeowners that don’t understand these seasonal preferences of their lawns have all sorts of problems and frustrations.

Now, apply this same illustration to your shrubs, trees, perennials, flowers and vegetables. Ceanothus, aeoniums, sweet peas, lettuce, rosemary, live oaks, olives, acacias and matilija poppies are like a fescue lawn, they thrive in the cool half of the year and sulk in the summer. Hibiscus, bougainvillea and lemon trees are like bermudagrass, they prefer the warm half of the year and despondent in the winter.

It’s also easy to see the distinction between a cool-season plant and a warm-season plant when observing annuals, since they just shrivel up once their happy season ends. Primrose, pansies and poppies in the winter and petunias, marigolds and zinnias in the summer, obviously.

Let’s try a few more. Daffodils are cool-season, lilies are warm-season. Lettuce is cool-season, tomatoes are warm season. Follow along .  .  .  cilantro is cool season, basil is warm season. Peas in the winter, beans in the summer. Are you getting it now?

Bigger, evergreen perennials, shrubs and trees makes the cool season-warm season distinction a lot more blurry, but if you watch your plants and get to know them, they’ll tell you what they like by how they behave. Groundcovers, like iceplant, blue fescue, gazania, baby tears and rosemary grow and look their best during the cool months of the year, while verbena, mondo grass, honeysuckle and lantana want warm weather.

Why does any of this matter? It matters because it tells a gardener almost everything about the “when’s” of a plant; when to plant, when to prune, when to water, when to fertilize. Just as important, it tells the gardener when not to do certain things. Planting, pruning, watering or fertilizing at the wrong time of the year can do serious damage to many plants, even kill them.

Just as important, this knowledge of warm season-cool season helps one design and arrange the plants in their garden for maximum success and simplified maintenance. A cool season ceanothus in the midst of warm season pittosporums is a recipe for disaster, just as an olive is when surrounded by geraniums.

So watch your plants and learn from them. Understand their seasonal preferences and provide for them appropriately. If you do, you will become a better gardener. You will understand why the aeoniums are shriveling, the sweet peas are drying and the daffodils are done.

Ron Vanderhoff is the Nursery Manager at Roger’s Gardens, Corona del Mar and his profile can be seen at www.themulch.com/my-profile/609-ron-vanderhoff.

Questions from Readers June 26.

What’s the best fruiting pomegranate tree for local gardens?

Beth, Laguna Beach

Answer:

Look for one called ‘Wonderful’. Pomegranates are excellent small trees in a Mediterranean garden setting and are quite drought tolerant as well. Their somewhat twisting, irregular growth, bright orange flowers and attractive brick red fruit provide four season interest.

Look for one called ‘Wonderful’. Pomegranates are excellent small trees in a Mediterranean garden setting and are quite drought tolerant as well. Their somewhat twisting, irregular growth, bright orange flowers and attractive brick red fruit provide four season interest.


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