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Gardener's mailbag: Why are my hollies yellowing?

By Neil Sperry
Special to the Herald Democrat

Dear Neil: I have some older hollies that have always looked good. Now, however, they are developing yellowed leaves. Should I be concerned?

Holly with old yellowed leaves preparing to shed

I cannot answer without more details or a photograph, but I can help you diagnose the issue yourself. If it is solely older leaves at the bottoms and within the middles of the plants, those leaves are about to be shed as new growth is produced this spring. If it is new growth at the tips of the branches, and especially if you live in an area where soils are alkaline, it is very likely due to iron deficiency. Iron deficiency also manifests with the veins holding their dark green color longer than the rest of the leaf blades. In this latter case, you could try applying a liquid iron and sulfur soil acidifier to the ground in April and again in June and September. Hopefully that would supply enough iron to meet the plants’ needs.

Dear Neil: What is the best time to apply pre-emergent weedkiller granules in the spring?

Squash plants ready to produce In spring garden

Folks are really asking early this year. Timing varies with where you are in the state. Every gardener must find the average date of the last killing freeze for their own part of Texas. Pre-emergent application normally should be 2 to 3 weeks prior to that time. And the second round (“booster shot”) would come 90 days later. The products to use would be Dimension, Halts or Balan, among others. I choose not to give specific dates this far out because late winter weather can cause them to shift by a few days, also because Texas is such a giant state. Normal timing for first application will range from February in deep South Texas to April in far North Texas. I want my readers to do the little bit of “homework” of knowing their average last-freeze date.

Dear Neil: I am recently retired and wanting to start a new garden. What would be some good vegetables to grow?

My advice is always to start small and manageable. Your garden should be in full sun, and perfect drainage is critical. Raised beds of well-prepared garden soil give the greatest yields. Let’s work backwards on your list. Avoid vegetables they take huge amounts of room. That would include corn, okra, watermelons and other melons. Rule out any vegetables that you and your family just don’t care for. There’s no point in growing them just to look at them. Don’t grow types that are known to be very difficult. Then, with what is left over, take a look at the list and choose your favorites. Read up on them and what they need to be productive in your garden. Choose the best varieties of each. Buy the best types of hybrid seeds. It may cost several times more than old garden seeds, but the resulting plants will out-yield the old varieties several fold. You spend a few cents more per plant, but you get pounds more produce. That sounds like a great trade.

Tomatoes do best in cages

Tomatoes are, by far, the most popular vegetables in American gardens. Stick with Texas A&M-recommended small and mid-sized varieties. Peppers, bush green beans, squash, onions, Irish potatoes, leaf lettuce, cabbage and broccoli would be in most people’s “A” list. Know each crop’s optimal planting date and be sure that you hit it.

Dear Neil: For the past several years I have dried my horses’ manure and used it as compost and fertilizer for my vegetable and flower garden plants. Recently, however, I’ve heard that hay growers use herbicides to keep down weeds. I’m worried that it might pass through the manure and make my compost unsuitable. Thoughts?

I would think that would be rather unlikely. However, dedicated organic gardeners might prefer to use hay that had been produced without use of herbicides. But to persist through the hay, into the horse, through its digestive system and into the manure, then through the composting process and up into the plants? That’s a long journey. Time and moisture would probably have taken the herbicide out of the system. If any herbicide remained, you would be able to monitor its presence by its impact on the growth of your flowers and vegetables. If those were my gardens I wouldn’t worry, but it’s a decision you have to make.

Dear Neil: I have an oak with a cavity. Can I use some type of wood filler to fill it and even the surface out?

Certified arborists advise against that. Filling cavities adds no strength to the tree’s trunk, and it encapsulates any decay that might be present. You’re really better off just allowing the tree to form new bark across the open wound. If you see a roll of bark forming uniformly across the opening, you’re on your way. If it is not forming, and if the decay seems to be getting worse, you need to call a certified arborist for an on-site inspection.

Dear Neil: I have just gotten my soil test results back from Texas A&M. They seem really odd, because I want to work up a vegetable garden area, and the tests say I should add only nitrogen. Don’t I want phosphorus for vegetable production?

Yes, you do want phosphorus for roots, flowers and fruit, so your question is very logical. What the soil test has obviously discovered is that your soil already has excessive amounts of phosphorus. That’s extremely common in Texas soils, especially if fertilizers containing phosphorus have been added in the past. High levels of phosphorus can adversely impact the solubility of critical minor elements, resulting in poor plant growth. Trust the soil test. Apply a high quality, all-nitrogen plant food.

Have a question you’d like Neil to consider? Mail it to him in care of this newspaper or e-mail him at mailbag@sperrygardens.com. Neil regrets that he cannot reply to questions individually.