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Ask a Master Gardener: Leaf raking, tree fertilizing tips and when to plant garlic

Ask a Master Gardener: Leaf raking, tree fertilizing tips and when to plant garlic

October 23rd, 2016 by James Quinn/Regional Horticulture Specialist in Life & Entertainment

Q. Is it OK to mow up leaves instead of raking them? Does it hurt the grass?

A. One way to clear the lawn and recycle leaves is to mulch them into the turfgrass. This can be a dusty affair, so one way to reduce this is on a dewy morning when the leaves are still damp. Adjust your lawn mower to its highest setting, and start mowing. By using a crisscross pattern and double-mowing, leaves often can be reduced to the size of confetti. The tiny pieces of leaves will gradually filter into the lawn and begin to decompose. The result will be the release of nutrients for use by the turfgrass. Research has demonstrated that a layer of leaves up to 6 inches in thickness can be mulched into the lawn with no ill effects.

Q. I've heard that one shouldn't fertilize trees in the fall, then I recently had someone else say fall is the best time. Which is it?

A. Fertilizing after mid-July may stimulate late growth that can be damaged by an early freeze. If fertilizer is required, it can be applied any time from late September through early April.

Often, best results are obtained when fertilization is done after the first hard freeze in October or November, but before the soil freezes in December. During this period, the soil temperature is still warm enough for roots to take up minerals, which are then stored for growth the following spring. Fertilizer applied during winter may be lost to leaching or runoff. The second-best time to fertilize is in March or April, just before new growth begins.

Q. I removed some brush and now have bare ground. I would like to plant it to a turf mix next spring. Can I still seed something to cover the soil?

A. You have a couple of options, and both have their downside. Oats could work out great, but you may not get much growth before it gets too cold. If we have mild fall weather, it is the best option, as you should get good growth and decent cover on the soil. The benefit of oats is it winterkills in Missouri, so you won't have green growth to contend with when you want to seed early next spring.

Winter wheat or cereal rye is another option. These normally survive the winter and thus hold the soil better, even if their top growth isn't that much. But come spring, you'll need to kill them. If you were planning to till up the soil, it will work up harder. If you want to kill them with an herbicide, you need them to green up and start growing to get a good kill. They might not be ready for this until mid- to late March. In either case, fertilizing the cover crop once up with some nitrogen will boost their growth.

Another option would be to mulch the ground with something like straw to protect it. Putting a light layer of straw over a spring seeding of turf is good, so you could rake the straw up in the spring and then put it back down after your soil prep and seeding.

Q. I transplanted some pin oaks last year, and they looked good most of the summer. Late summer, their leaves turned yellowish. What is this, and how do I fix it?

A. Pin oak trees are somewhat susceptible to developing iron chlorosis. This is low availability of iron to the tree. Generally, it is not caused by low iron, but by a higher pH in the soil. When soil pH is alkaline, or above 7, iron is less available to plants, being bound more tightly in soil particles.

To fix the problem, the soil pH needs to be lowered, generally attained by adding sulfur. To know how much sulfur to add, a soil test is needed. If larger trees develop yellowish leaves where before they were nicely green, it is often because their roots grew into alkaline soil. This commonly occurs with soils adjacent to driveways, sidewalks, and building foundations. Cement is quite alkaline and most gravel is from crushed limestone, which is alkaline. When sulfur is added to the soil, it takes up to six months to take full effect. So correcting an underlying problem like this in the winter is ideal, as the plants come spring should respond well.

Q. Is it too late to plant garlic?

A. No, it is not too late. Garlic can be planted until early November in Central Missouri.

The Central Missouri Master Gardeners are a volunteer group of 191 members, 122 of whom are Cole County residents, who maintain 11 beautification sites in Cole County, which are nonprofits or public entities. Master Gardeners must complete a basic training program of at least 30 hours of horticultural training, as well as 30 hours of volunteer service. The Missouri Master Gardener program is supported by the University of Missouri Extension.

Have a gardening question of your own? Call 573-634-2824 or stop by the Cole County Extension Center in Jefferson City at 2436 Tanner Bridge Road.