GARDENING : SURVIVE SUMMER'S HEAT WITH CAREFUL PLANTING, WATERING.

Byline: Joshua Siskin

Bears may hibernate in the winter, but July signals the beginning of an extended period of dormancy for many Valley gardeners. The heat is on for the next several months, and you cannot blame people for seeking cooler pleasures than digging and weeding in the sun.

In fact, caution is the word with regard to certain plants that are almost sure to suffer from July planting. One of the most famous of these is annual periwinkle or vinca (Catharanthus roseus), the plant with those captivating pinwheel flowers in lavender, red, pink or white. When planted in hot weather, vinca is almost sure to quickly develop a fungus disease - indicated by wilted leaves - and die.

Even petunias, which look great this time of year if they were planted in early spring, should probably not be planted again until the latter part of August when - no matter how hot it gets - the shorter days make garden acclimation easier than at present. Like vinca, petunia is quick to develop fungus diseases when planted during the long, hot days of July.

If you are thinking of planting California natives, you might want to delay this activity until the fall. If native plants are already growing in your garden, water them with caution. Do not, under any circumstances, water native plants on a warm evening. Wet soil on warm nights is sure to invite the growth of Phytophthora, a soil-dwelling fungus which is lethal to ceanothus, manzanita and just about every other California native.

There is a cultural practice that will extend the planting season for annuals and perennials into July and beyond. This is the practice of building raised beds. Raised beds, which should consist of sandy top soil (available at the nursery in cubic-foot bags) and homemade compost (or Nitrohumus or Gromulch), are the surest way of growing flowers, vegetables and perennials to their maximum potential.

To build your beds, start by turning over and excavating your existing soil with a spading fork and round point shovel. The deeper you can dig, the better the drainage, the more oxygen there will be for your plants' roots, and the faster your plants will grow. Now add topsoil and compost to the turned-up earth - as much as you can haul and mix into your emerging beds before exhaustion or backache sets in!

Confine your efforts to 3-foot-wide strips. That way, you will never have to step into the narrow beds you are creating when it comes to weeding, watering or harvesting.

Although raised beds are most commonly associated with vegetable growing, annual flowers and perennials will also grow well in them. Plants that are supposed to flower on and off - perennial salvias and ground covers such as gazania and verbena, for example - may flower virtually year round in a raised bed.

Some gardeners I know have soil that is little better than rock or indurated clay. Chatsworth, Simi Valley and Thousand Oaks are notorious for harboring soil that can crush the spirit of the most energetic gardener. Just the thought of digging in such soil is enough to make you want to take a nap. Where soil is too hard to dig in, consider building a sand box 8 to 12 inches deep and filling it with topsoil and compost. Grow vegetables, flowers and perennials in your own boxed, designer soil and forget about the unworkable earth that lies below.

Given adequate soil preparation, the following vegetables can be planted in July with confidence that they will produce a reasonable harvest by summer's end: beans, corn, cucumbers, tomatoes, Swiss chard and summer squash. Root crops such as radishes, carrots and beets can also be planted; since their edible portion - the root - never sees the light of day, they will succeed with only a half day of sun. Nearly all other vegetable crops require full-day sun exposure.

As for annual flowers, several are still plantable in July, including: bachelor button, cosmos, marigold, nasturtium and zinnia.