Rains Wash Away Soil’s Nutrients

QUESTION: My lemon tree is getting some yellow leaves, and I know it would appreciate something to nosh on. However, with all the rain, when do I feed my plants?

--S.S., Granada Hills

ANSWER: Yellow leaves are not a sure sign that the lemon needs fertilizer. The soil could also be too wet. Garn Wallace, soil scientist at Wallace Laboratories in El Segundo, told me that simply looking at the tree isn’t enough. “It’s hard to differentiate between waterlogged plants and ones that need nitrogen,” he said, and both can be a problem in years as rainy as this.

A leaf analysis at a lab could tell you exactly what the trees is suffering from, but he said that if the younger, newer growth is greener than the rest of the tree, it probably needs nitrogen. Water-logged plants tend to turn yellow all over.

Before you fertilize, check the base of the tree and make sure rain water is draining away from the trunk and that the soil hasn’t become too wet.

When it rains as heavily as it has, nitrogen and calcium are the first elements to be washed from soil.

To replenish lost nitrogen, Wallace suggests using plain ammonium nitrate, sold in bags at nurseries. It’s strong, so you have to use it carefully, but it’s inexpensive, works quickly, is pH-neutral and isn’t easily washed out of the soil.

Simply scatter the ammonium nitrate around plants. Don’t overdo it. Add no more than three pounds of ammonium nitrate per 1,000 square feet, and wash it off foliage.

To replace lost calcium, an important buffering agent, add gypsum to the soil at a rate of 5 to 10 pounds per 1,000 square feet.

Most of the other elements in common fertilizers are already abundant in Southern California soils, but if you think you need to add other kinds of fertilizer, have your soil tested by a soil laboratory.

The best time to apply is just before one of our spring rains. Rain is expected to continue this month, so try to scatter the fertilizer over the soil just before a storm is predicted. If the storm is a no-show, water the nitrogen into the soil with a sprinkler. A few minutes should do it.

Gardeners can also use a slower-acting but longer-lasting organic fertilizer, such as blood meal or the faster bat guano. Lightly cultivate these into the soil, which means barely scratching them into the surface with a cultivating fork.

Even with the organics, don’t use as much as the package recommends unless you are really trying to get some growth out of new plants.

On the plus side, growth inhibitors, such as sodium, have also been washed out of the soil, making nutrients more available to plants.

Cauliflower, Sprouts Find a New Garden

Q: This is my first time growing Brussels sprouts and cauliflower. I know to tie the leaves over the forming cauliflowers, but what do I do when the Brussels sprouts begin to form? Are the leaves edible like collards and kale and other greens?

--B.B., Los Angeles

A: At first you don’t need to do anything, just let them get fatter. The trick with both vegetables is not to let them go too far. You don’t want your edible buds blooming.

Let the dense heads keep growing, but as soon as they begin to loosen--when the buds are no longer packed closely together--it’s time to cut.

If cut about 4 or 5 inches below the head, broccoli plants will develop many side sprouts that are just as delicious as the main head.

Incidentally, many newer cauliflower varieties don’t need to have their leaves tied over the developing heads. Called “self-blanching,” they will stay white even exposed to the sun and will not turn that creamy color.

Both Brussels sprouts and cauliflower freeze nicely if your harvest comes all at once.