When is the best time to plant a tree?
Of course we’ve timed our answer to this question to the absolute perfect season for planting trees, autumn. With shorter day-lengths, cooler temperatures and maybe even a little rainfall, autumn has everything that a tree needs to keep transplant stress to a minimum. Most of the trees that we plant in Central Texas are deciduous, so they’ll soon be dropping all their leaves and going dormant to avoid the damaging cold of winter. During the winter, with no growth happening above ground, trees are free to focus their resources below ground, on their roots. If planted in the fall, trees have almost half a year to establish their root systems before the temperatures get overbearingly hot and they start to need more water to survive. In order to take up water, plants must release water into the environment through a process called transpiration. During the heat of summer, the air is so hot and dry that it practically sucks the water right out of leaves. Which is why during extremely hot weather, many trees drop their leaves and go dormant during the summer. Dormancy is simply a plant’s way of avoiding stress. It takes a lot of water to support a canopy full of leaves, and if there isn’t enough water, which is a pretty stressful situation, a good strategy is to drop those leaves and go to “sleep” until the stress passes. So if you’ve ever planted a tree during the spring, especially in the late spring or if summer has arrived early, you may have noticed that your tree immediately dropped all of its leaves and struggled to survive all summer long. But I bet once the temperatures began to drop and the sun became less intense a few months later, new leaves appeared and the tree took advantage of the short autumn window to get just a little bit of growth under its belt before winter and its true dormant season arrived. The lower temperature and higher relative humidity of fall help to keep trees better hydrated. So planting during autumn gives trees more time to acclimate to their new environment, your yard, and get established.
What’s the difference in soil, compost, and mulch?
Well, they’re all used in similar ways, and have a lot to contribute in our gardens. We could spend days discussing and defining soil, but one good way to think of it is the substrate that your plants grow in. Soil is made up of varying amounts of sand, silt and clay. If you’ve got a good balance of these three mineral elements, your soil is called “loam.” Too much clay leads to sticky, heavy soil that inhibits plant growth, and too much sand leads to leaching and a lack of water-holding capacity. Silt is somewhere between clay and sand as far as size, texture, and effect on overall soil structure. If you’re lucky, your soil also has a good amount of organic matter and a healthy microbial population. But you might be surprised to learn that a soil with only 5% organic matter is pretty fabulous, and it’s hard to even get that much. Compost is pretty much all organic matter, depending on the ingredients that went into it: grass clippings, leaves, and kitchen scraps. And maybe a little bit of soil if you’ve added some from your garden, which would be a good thing, since your soil contains the necessary microbes to break down the organic matter in your compost pile to a size and texture that is beneficial in your soil. Compost helps to increase the water-holding capacity of your soil without over-doing it. It helps to break up heavy clay soils and helps sandy soils hold a bit more water. It builds the structure of your soil, giving it just the right balance of air and water. Compost also feeds the microbial population, helping to keep them around and contributing to your overall soil-health. And mulch is ground up plants parts that are not composted and are generally larger pieces than compost. Pruned tree limbs that have been processed with a chipper/shredder; bark pieces; and even processing byproducts, such as pecan shells and cocoa hulls, can be used as a mulch. Mulch is generally all carbon, as opposed to compost, which contains both carbon and nitrogen. Compost may also be used as a mulch, since the primary purpose of mulch is to protect the soil from the environment by covering it. Both compost and mulch eventually break down, due to the weather and the action of microbes, which is why it should be replenished at least yearly.
Why do we firm the soil around new plants? And if firming the soil is good, why are we not supposed to walk through our garden beds?
When digging a new hole for a plant, you’re basically destroying the soil structure in that area, so you want to put it back as close as possible to the way it was. Tilled soil has increased fluffiness and larger pore space, which increases the space for air in the soil, which is not necessarily a bad thing, especially for a new planting. But those larger, air-filled pores are too large to hold on to water, which could very well be the kiss of death for a new transplant in a very short time. That’s one reason why you should water new transplants every day, if not twice a day, for a while. This is about more than just the plant’s lack of roots, it’s about the soil settling and the pore-space decreasing over time. Once the soil is settled back to the way it was before you dug your hole, it will begin to get back to the natural structure and water-holding capacity that it had due to its natural texture, which is dictated by the amount of sand, silt, clay, and organic matter that makes it up. If you’ve heard of no-till farming, you’re familiar with this concept. Disturbing the soil structure as little as possible, except, obviously, in the planting hole, is best for overall soil structure and overall health. But, there’s also soil compaction to think about. If the soil is walked on extensively, or driven on, in the case of construction with heavy equipment, the pore spaces are squeezed together, leaving no space for air, and eventually, no space for water, either. Obviously, plant roots need water, but they also need oxygen to breath and be able to take up the water and life-giving nutrients that are in the soil. Compacted soil also becomes very hard, making it almost impossible for roots to push out into it. And when roots can’t grow, the rest of the plant’s growth is also impeded. Lack of rainfall, especially if you’re unable to irrigate, also leads to soil compaction. Like a sponge when it dries out, your soil shrinks in on itself, decreasing pore space and making it very hard to re-wet without squeezing it. And I don’t have to tell you that you can’t squeeze your soil. During extended heat and drought, Central Texas soils become very compacted, adding yet another stresser to plants, especially in natural areas where there was no way to irrigate them and alleviate the problem. So soil compaction should be avoided at all costs.
The key to success with drought tolerant species- SOIL
Our question this week was prompted by the flurry of emails that I got after our recent heavy rains. A lot of people had plants falling over, and some were even splitting apart. All of the plants in question were drought tolerant choices, which are a hugely beneficial addition to our gardens in the current years-long drought. But this situation offers me the opportunity to talk a little about the key to success with drought tolerant species, and that’s soil. If you live in an area with heavy clay soil, and many of us do, low-water-use plants will struggle when we actually have rainfall. Many of these species are native to desert regions, where the soil is very porous. So in their native environment, even if it rains, the soil doesn’t hold water for long. But that’s not true of our clay soil, which holds water for a very long time. And if desert species, which are adapted to very dry conditions, stay wet for too long, they will rot and fall over. Artemisia, Senna, Cassia, Agaves, and Yuccas are just a few of the plants that suffered in the recent deluge of rain to Central Austin. That’s just too much water for most desert species to handle. If you can, build berms or raised areas in the garden for desert, drought-tolerant species. And use very sandy, porous soil to amend those planting beds. Raising the roots out of the heavy clay soil helps to keep them a little drier. It’s a great idea to move to more heat and drought tolerant species, but we need to understand how to change the entire landscape to better mimic the natural environment of these plants. Building berms and swales, to channel the water away from certain areas of the garden and into others, will go a long ways towards insuring the success of low-water use species. One viewer asked if he could pull his Senna back up, tie it together and get it to recover. Sadly, no, this won’t work.
Pink fairy duster,Calliandra eriophylla
This beautiful little West Texas native shrub, with its dense branching habit and tiny leaflets, is often referred to as straggly. But in spring and summer, when it’s covered with hundreds of puffy pink flowers, you’ll discover why it’s such a beautiful addition to your landscape. Although it may remain evergreen in areas where winters are very warm, it is deciduous in Central Texas. Pink fairy duster won’t need any supplemental irrigation if we’re getting even small amounts of rainfall, but if we have a particularly long dry spell during the hottest part of summer, it will benefit from a little extra water once a week or so. It does best in rocky, gravelly soil, so if you have heavy clay soil, this plant won’t do as well for you. Pink fairy duster gets about 3 feet tall and wide, so give it plenty of space. It also needs the full, bright sun to perform well and be happy. It produces lots of seeds that are easily sown, but grows only moderately fast, so don’t expect it to fill in overnight. If you want to collect the seed, you’ll need to time it just right, since the pods pop open, and send the seeds flying, once the seeds are ready. There’s also the Baja fairy duster, Calliandra californica. If you like red flowers, you might like this one better. It also gets a little taller and wider, up to 6’ tall and 8’ wide, so give it a little more room. Baja fairy duster is not as cold hardy as the pink, listed only to zone 9a, much warmer than we are here in Central Texas in zone 8b, so in “normal” winters, be prepared to start over with this one.
This particular Salvia greggii cultivar behaves much the same as the species, but the flowers have a more intensely velvet look to them. The flower is a little fuzzier, which gives it a different texture and a deeper color. Although it is a low water-use plant, it will definitely perform a little better if you water it once a week during the heat of the summer. It flowers from spring right on through fall, with maybe a little break at the peak of summer heat. But once temperatures cool just a bit, the sun becomes less intense, and we get just a little bit of fall rain, ‘Cardinal Velvet’ comes roaring back to life. It is listed as hardy to zone 8, so if we have a particularly harsh winter, you might lose this one if you can’t protect it. It’s also evergreen, making it a wonderful spot of deep green color in your winter landscape. Like all Salvia greggii’s, ‘Cardinal Velvet will truly benefit from a harsh pruning in late winter, and even again in late summer, to get rid of that rangy growth and encourage it to bush out and become full again. Don’t be fooled by this plant’s small stature in the container, it can get up to 3’ tall and wide, so give it plenty of space. It can take the full sun, but I’ve found that mine performs a bit better with some protection from the intensity of afternoon rays. ‘Cardinal Velvet’ looks great planted alone in an open space in your garden, but also looks fabulous when planted in masses, or as a short border around planting beds.
Agarita, Mahonia trifoliolata, aka Berberis trifoliolata
This rounded shrub has leathery, spiky, holly-like foliage, only the leaves are more gray-green than the deep green of hollies. It’s evergreen and has no problem surviving our winters, OR our summers here in Central Texas. This plant is as tough as it looks, and although it thrives in the full sun, it also does just fine in a bit of afternoon shade. It can get a little monstrous, up to 6’ tall and wide, and even bigger, if rain is plentiful, so give it plenty of room to spread. The delicate yellow flowers of agarita appear in late winter and cover the plant from February ‘til as late as April, depending on how cold our winter is and how late our last frost arrives. The flowers are followed by bright red berries, from about May through July, which are a great source of food for any wildlife and birds in the area. YOU can also harvest the berries and use them to make jelly, if you’re so inclined. And agarita is a great cover plant for animals, serving as a nice, evergreen habitat for many different types of birds during the cold of winter. It does perform best in well-drained rocky soils, so if you have a very heavy clay soil, you might consider another choice, maybe a Pyracantha. The flowers of agarita are fragrant, so if you have a spot near your porch or a walkway where you can plant a spiky, very large shrub, you’ll enjoy this plant even more.
An easy to grow herb that brings beauty to the garden. With its feathery bright green foliage and lovely upside-down-umbrella shaped inflorescence, dill makes a striking addition to any area of the garden. Dill is frost tender, so plant in late spring, once all danger of frost has passed. The seeds are very small, and should be scattered and lightly scratched into the soil. Dill thrives in well-drained soil with lots of organic matter. Since dill is an annual, you’ll have time between growing seasons to amend the soil and compost each year. I find that tucking one or two annual herbs and flowers into my established landscape areas really helps to bring new life to the yard, and dill is a great herb to bring a little spring cheer back to a struggling summer garden. Dill is a host plant for the black swallowtail butterfly, so be prepared to share your plant with some beautiful visitors. Dill grows very quickly and may tend to fall over, especially if exposed to windy conditions or if planted in too much shade. So be sure to give it at least 6 hours of sun and plant in a protected spot. If you’d like to harvest the seeds for cooking, cut the entire flower stalk just as the seeds begin to ripen, and then allow the stalk to dry. You can also use dill leaves in pickling, soups, and other savory dishes. Harvest fresh leaves and use them immediately, since the flavor is lost fairly quickly. Cutting your dill to use in the kitchen will actually invigorate it, causing it to branch and grow and produce more leaves and flowers for harvest.