Do you have a gardening question? The UC Master Gardeners of Santa Clara County can help. Our volunteers are part of the University of California’s Cooperative Extension program, and we are trained to use research-based information to educate residents on sustainable gardening and landscaping practices specifically for our area.
Our monthly “Ask a Master Gardener” column will answer your questions and offer tips. Have a question? Email lifestyle@embarcaderopublishing.com.

Your gardening questions answered

I’m noticing yellow leaves on my citrus tree. What’s wrong and what can I do about it?

While there are several possible causes for yellow citrus leaves, the most likely one in
winter/early spring is that citrus roots do not absorb nitrogen efficiently from cold, wet soils. There may be adequate nitrogen in the soil, but the roots aren’t able to take it up. However, if the tree doesn’t green up when the weather warms, give it some nitrogen fertilizer, up to 1 lb. of N per year for a mature, full-size tree. Dwarf trees or ones in containers require less fertilizer, 1/2 lb. of N or less. Do not overfertilize since that may cause other problems.

I’ve noticed a white substance underneath my mulch. What is it and should I remove it?

It can be alarming to see what’s growing under your mulch, but not to worry! The white cottony or crumbly substance is mycelium, which is the intricate root system of mushrooms. The thread-like filaments are evidence that soil fungus is breaking down the mulch to release essential minerals to the plants’ roots. It’s a normal part of the decomposition process. You can just leave it in your soil but if you want to make your mulch last longer, you can break it up and keep the mulch as dry as possible. Since any organic mulch will break down over time, it’s a good practice to occasionally add a new layer. Want to learn more about mulch molds? Click here.

Gardening tips for March

Wait to remove dead bulb foliage

You may be enjoying a profusion of daffodils, tulips and other bulbs right about now, but at some point soon, their blossoms and foliage will start to die back. It’s tempting to cut them back — but wait. To keep bulbs blooming each year, leave the plant’s foliage in the ground long after the blossoms have withered. That’s because the foliage — the stem and the leaves — continue to channel energy to the bulb needed for next year’s blooms. Deadhead (cut off) the spent flowers to prevent them from creating seed pods. Then wait for the foliage to die back and turn yellow before removing it. Some people tie the leaves together to tidy the garden, but that’s not advised because it limits the light needed for photosynthesis. Instead, intersperse annuals to hide the foliage until it can be removed.

Start summer vegetables from seed

March is a great time to start summer vegetables for transplants. Seeds started now will be ready to transplant in April or May, perfect for warm-weather lovers like tomatoes, peppers and more. On our vegetable planting chart, the last column “From seed to transplant” tells you about how long it takes for seeds to grow into sturdy seedlings. Tomatoes take about six weeks, while zucchini can be ready in as few as three weeks. Plan when you want to transplant into the garden, then calculate backward to figure out when to start seeds.

petal blight is caused by a fungus that continues to live in the soil once a plant is infected. To reduce outbreaks, pick off all infected flowers and dispose of them in green waste. Home composting is not hot enough to destroy the pathogen. After blooming, pick up any petal debris. Then spread fresh mulch around and beyond the bush (but keep the mulch a few inches away from the trunk).

Pull those weeds now

Plentiful rain and mild temperatures mean that weeds are springing up all over. The moist soil makes it easier to pull weeds now. It’s especially important to pull or shallow hoe annual weeds before they go to seed, which happens surprisingly fast. For perennial weeds like bermudagrass and bind weed, prevent re-growth by digging out as much of the root as possible, as well as any creeping stems. Wondering what kind of weeds you have? Use UC’s weed references and weed identification tool.

Do you want to ask a UC Master Gardener about a plant problem? Submit questions to our Help Desk online. Find garden events and classes here. Ask questions or listen in at our monthly Zoom Plant Clinic which is held the second Tuesday of the month from 7:00 – 8:30 p.m. Dates for 2024 are March 12, April 9, May 14, June 11, July 9,
Aug. 13, Sept. 10, Oct. 8. You can also subscribe to our monthly Tips and Events newsletter and to our seasonal Thyme to Garden blog. San Mateo residents can also find gardening advice on the UC Master Gardeners of San Mateo and San Francisco website.

Source: paloaltoonline.com