Question
My Christmas cactus was outside while gone for holiday and was hit by frost. The leaves are wilted but after a week have not died. Is calcium good for cactus or is there something better to help it along?

Answer
Hi Debbie,
  When plants are exposed to frost, it has about a 50% chance of recovering. A few things that can determine if a plant recovers or not are the type of plant, the extent of the damage and how healthy the plant was before. One of the most important things is the care the plant receives after it is damaged by frost.

Be especially careful to water the plant properly. You do not want the plant to have any additional stress put on it. As a general rule, you should allow the top 1-2 inches of soil to dry between watering. Then water just enough for a small amount of water to drain out of the drainage holes in the bottom of the pot.
For the next several months, I would recommend that you water the plant with distilled water. Fluoride, chlorine, hard water deposits and other chemicals found in most tap water can cause problems for some plants. Usually it is specific kinds of plants that are sensitive to those chemicals that have the problems that are commonly caused by tap water. Plants that are not normally sensitive to those chemicals can be affected by them when the plant is unhealthy or damaged.

Christmas cactus is not really a cactus and it will not do well if the soil is allowed to get too dry or kept too dry. In fact, the soil drying out completely could be fatal to a Christmas cactus.

Put the plant in a place where it can get bright, but not direct, sunlight.

Remove all of the dead and damaged leaves. Usually I recommend that you not remove more than 50% of the leaves. However leaves that are severely damaged (or dead) need to be removed. Damaged leaves will never heal (although wilted leaves can sometimes make a good come back).

It might take awhile for the real extent of the damage to appear. Even leaves that mostly look okay right now could turn brown or black over the next few weeks or so.

Do not give the plant fertilizer. Fertilizer will not 'cure' an unhealthy or damaged plant. It will actually only cause more harm. You can fertilize the plant VERY lightly once it is producing a large amount of new growth and there has been no further damaged leaves.

Also you should not give the plant calcium. Plants do need calcium, but calcium deficiency in houseplants that are planted in pots with commercial potting soil is rare. Calcium deficiency in plants is most commonly caused by excessive use of fertilizer that has high concentrations of potassium or nitrogen. Most commercial fertilizers are fairly well balanced. Also soil that is way too acidic can cause a calcium deficiency as well. Most commercial potting soils are formulated to have a pH of 7, which is generally considered to be neutral.

Good Luck
I hope this helps. If you have any questions or need additional information please don't hesitate to ask.
    Thanks
      Tracy