Ask the gardeners

I read a reference recently about ''hardening off'' plants. Would you please explain exactly what this is? ''Hardening off'' means gradually conditioning indoor-grown plants to outdoor conditions. This can be done by moving the plants to a cold frame, where the cover can be removed a few hours each day to expose plants to lower temperatures.

If you have no cold frame, you can move plants outdoors daily to a porch or spot near the house foundation where they're out of strong wind but get several hours of sun.

The temperature change should not be drastic; outside it can be 10 to 12 degrees lower than indoors. As night temperatures moderate, the plants can be left outside altogether.

Withhold fertilizer until planting in the ground.

We would like to grow a few vegetables, but really have no space for an ordinary garden. Would it look strange if we grew some tomatoes, peppers, herbs, and cucumbers among our evergreens? Are there compact varieties?

A friend of ours has for several years spaced potted vegetables artistically in her foundation planting. For tomatoes, try Florida Petite, Patio, Small Fry, Sweetie, Tumblin' Tom, and Burpee's Pixie Hybrid (some may need a little staking).

For hanging baskets try Florida Basket, Goldie (yellow), and Basket Ring. All pepper plants are easily grown in pots, as are short-growing herbs. Spacemaster and Bush Champion are excellent pot cucumbers. Patty Pan bush squash is prolific in pots.

Our friend uses 10-inch-square wooden boxes with natural color.

When planting a shrub or tree with a wrapped ball of earth, should the wrap be removed and should the twine be cut and taken off?

In the days when the wrap was made of burlap and the twine of hemp or other biodegradable material, the wrap could merely be loosened and the twine cut where it wrapped around the trunk.

However, today most wrap is made of plastic, even though most of it is meshlike and may resemble burlap. Almost all twine is plastic or nylon.

If left on, the wrap will inhibit root growth and the twine will girdle the trunk so that it cannot grow, thus cutting off the flow of water and nutrients. We see many improperly planted shrubs and trees that succumb a year or so after planting, as the trunk and roots are strangled.

Caution: When planting bare-root plants, do not wind the roots together. Spread them out so they do not girdle one another or the trunk.

I've been seeing a great deal lately about soil pH, but I do not understand the term. Could you give a simple definition?

It is a scale for measuring soil acidity or alkalinity. A pH of 7 is neutral. Any number below 7 on the pH scale denotes acidity or ''sourness,'' any number above 7 denotes alkalinity or ''sweetness.'' From 7 down to 6 is slightly acid; 6 to 5, moderately acid; and 5 to 4 and below, strongly acid. The same is true on the scale in the reverse direction.

A large percentage of fruits, vegetables, and ornamentals prefer a slightly acid soil.

We have a white camelia in an 8-inch pot. Although the leaves look healthy and there is new growth, the flower buds continually fall off. Of several dozen buds, we've had only three or four full blooms over several months. What would cause this?

If the rest of the plant looks healthy, bud drop is usually due to too high a temperature or lack of water.

Camelias, when flowering, like night temperatures in the low 50s (F.), and days no higher than 68 degrees F. They should be kept moist (never soppy), and they prefer filtered, bright light.

Humidity should remain at 60-65 percent. Misting helps if humidity is not high enough.

Last summer, while on a trip to Ontario, Canada, we saw some lovely nasturtiums with variegated green and cream colored leaves. We cannot find them in any of our seed catalogs. Would you know who sells them?

They can be ordered from Stokes Seeds Inc., a firm that started doing business more than 100 years ago in Canada. Their address is 737 Main Street, PO Box 548, Buffalo, N.Y. 14240. The catalog is free.

We've grown Stokes Alaska nasturtiums for years, and always have many compliments about them.

The past two years our carrots have been bitter. It's the same variety (Chantenay) that we've grown for years, and previously they have been very sweet. Would you know the reason for the bitterness? We did grow them in a new location.

Carrots will become bitter if the soil becomes too dry, if they do not get enough nutrients, or if there's a problem with insects.

Work some rotted compost into the soil to help hold moisture, water during dry spells, and apply a balanced plant food at planting time and again at midseason. Healthy carrots are seldom pounced on by insects.