Q. I am starting a new vegetable garden, and I was wondering what the best soil amendment would be. I have access to free horse manure, but someone told me I would get a lot of weeds from it. Would peat moss or mushroom compost be better?

A. It's true that many weed seeds pass through an animal's digestive system intact and ready to sprout when environmental conditions permit, so you can wind up with a lot of weeds from horse manure. However, it can be a good soil amendment that increases the organic content as well as the fertility of your soil. Because you have ready access to horse manure, you can till it into your garden, allow the weeds to sprout, and then till them under or kill them with a nonselective herbicide such as herbicidal vinegar (20 percent, not the 5 percent vinegar found in your kitchen), a soap-based herbicide such as Sharpshooter or Roundup (glyphosate) before planting your vegetables.

To minimize weed problems, you might want repeat this process by tilling the garden again to bring more weed seeds up to the soil surface to germinate, then till them under or kill them. Then you should put down a 2- or 3-inch layer of mulch and disturb the soil as little as possible when you plant to minimize weeds. In light of food safety concerns, the USDA now recommends against using fresh manure within 120 days of harvest.

Peat moss is OK as a soil amendment, but it is nutrient-poor and tends to acidify the soil slightly. If your soil needs to be acidified, peat moss would be fine. You should have your soil tested so that you know what is needed to get the pH (acidity or alkalinity) into the optimum range of 6.2 to 6.8 that most vegetable crops prefer, as well as what specific nutrients are required.

Mushroom compost is a great soil amendment, but it has a high pH and also has a high soluble salt content. If your soils are too acidic and the pH needs to be raised for optimum vegetable growth, mushroom compost might be the best choice for your garden.

Q. My son bought me a beautiful Christmas cactus last year. It was completely covered with flowers. I was really looking forward to a repeat performance this year, but there are no flowers. The plant has grown and seems healthy, so why isn't it blooming?

A. Like poinsettias, Christmas cacti (Schlumbergera x 'Bridgesii') bloom in response to long nights. Fortunately, they are not nearly as fastidious about the long night routine as long as they are grown in cool temperatures. Your plant likely did not receive either the proper light regimen or cool enough temperatures.

Christmas cacti require cool temperatures in the fall to develop flower buds, between 45 and 55 degrees. Place them in a cool area in early fall to have them in full bloom for Christmas. Perhaps you have an unheated, attached garage. An unheated sunroom is perfect because Christmas cacti bloom best in bright, indirect light. They are understory plants in their native habitat and can actually be burned in hot afternoon sun. Do not allow them to be exposed to freezing temperatures.

Alternatively, you can alter the amount of daylight it receives and trick it into bloom. Christmas cacti and poinsettias require 14 hours of darkness every night to initiate flowering. Simply cover your Christmas cactus with a box or put it in a closet or an unused room from 6 p.m. until 8 a.m. Once the flower buds form, you can keep it in its usual place.

If you are moving your plant from place to place, be careful to maintain the same orientation toward the sun. Otherwise, the flower buds will try to point themselves toward the sun. If this happens repeatedly, they will weaken to the point of falling off the plant before they open.

Remember that Christmas cacti are jungle cacti rather than desert cacti. Water them as frequently as your other houseplants.

Doug Oster writes a blog, "Growing With Doug," exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.