Although the average last freeze in Dallas-Ft Worth is in the last part of March, you should remember that it is an average--half the time it will occur later. And a frost can occur at temperatures well above 32, especially on a calm clear pre-dawn. A light cover will usually protect from frost.
Repotting of deciduous trees should be pretty much over. Some slow species like oaks may be slow in coming outand could be repotted. Broad leaved evergreens, such as the hollies, usually start growth a little later and may still be repotted when their buds swell. Conifers and other evergreens should be in active growth and therefore not repotted. Newly repotted trees should not be wired until they show they have recovered.
Any trees that have wire on them should be watched very closely during the spring flush of growth. Branches and twigs can expand pretty rapidly and result in the wire cutting into the branch. Watch especially the junction of the branch with the trunk or a larger branch. Remove the wire if it is cutting into the branch and rewire if needed.
General care for all species is pretty much the same at this time. Feed, prune, and look out for insects and other pathogens.
What kind of fertilizer you use is not as important as that you use it right. Plants would like a small amount of nourishment to be available all the time. For bonsai, the best way to supply it is by using organic fertilizer cakes on the surface. They release nutrients each time you water and are held by the particles such as pumice to be used all day. Water soluble fertilizers are fairly good but the next watering will wash the remaining nutrients out. You wouldhave to water with it daily using a very dilute solution. Some organic fertilizers like bat guano or chicken manure release too much nutrients at once (are too hot). Many lawn and garden fertilizers are the same. Whichever you use be sure to follow directions.
Feeding needs to be done judicially. A lot of nitrogen will push the new flush of growth too much but with no fertilizer you will get foliage with poor color that lasts all year. The organic fertilizer balls are the best solution. You can add a few at the start and increase them as the foliage matures. If you use chemicals be sure to follow directions and too use them lightly at first. Also be sure to get a brand with the minor elements listed. Commercial water soluble fertilizers wash out with the next watering and result in poorly fed pale bonsai.
Most trees will do good in the fully sun at this time of year. However, if you have had them in partial shade be careful about giving them full sun. They probably should be acclimated gradually.
Whether you use the organic or chemical spray, the trick is to be sure to thoroughly cover the plant including all the leaf axils. Use a hand or pump up sprayer to get a fine mist spray to cover all surfaces, a hose end sprayer does not cover good enough.
Fungal diseases develop during warm humid weather. Too much foliage misting can do it also if the leaves stay damp very long. One of the most prevalent fungus is leaf spot which will hit several kinds of plants especially elms, hollies, and roses. Control consists of spraying with baking soda. A 1% solution of Hydrogen Peroxide can be used except on very young foliage which may be sensitive to it.
Remember when pruning that there is no one-size-fits-all, even on the same species. First of all, formation pruning is when you are doing the initial styling of the tree. In most cases you are trying to grow new branches requiring you to have the branches grow long. After the tree has been styled, you then need to do ramification pruning to develop twiginessand a patina of old age. To properly prune you need to know how they grow and to remember that new twigs, even in the far future, break from the internodes so keep them short.
On elms and other trees with leaves appearing alternately down the shoot, the first leaves are smaller and internodes short. As the shoot grows, leaves get larger and the internodes get wider. For developmental you can let these branches grow long to get thick and then cut back, leaving a few short internodes to sprout future branches, and regrow. For ramification let grow to 4-5 leaves and trim the last two. Repeat on the new twigs.
On maples and others with leaves coming in pairs on opposite sides of the twig, the bud send out a stalk with two leaves on the end. The length ofthis stalk will be the first internode. As the leaves open a new growing tip emerges and this process continues. As the new tip elongates the first stalk keeps elongating also until the third new tip breaks. This creates long internodes on the developing branch. If the second tip is removed as soon as it emerges the first stalk stops growing and two new twigs will develop from the first set of leaves.
For formation pruning on opposite leaved species, you must work to get short internodes near the trunk then later letthe branch grow for thickening. After the first set of leaves emerges, pinch the tip of the next set of leaves before they actually become leaves. Pointed tweezers are the best tool for this job as you want to get the growth when it just starts to emerge. Use this same technique through three sets of leaves, after which you can let the newly created branches grow to thicken. Each pinch results in two new leaf sets, creating shorter nodes to generate future branches. When the desiredprimary and secondary branches have been grown, the ramification is achieved by pinching the tip from each set of leaves as it grows thereby doubling the number of twigs each time. This can be a big job on a large maple, but is necessary to get the desired result.
Be sure to check your soils each day for proper water content. It is easy to assume that the soil has plenty of water when the days are cool or there has been some rain. Its too easy for a tree with full leaves to shed water outside of the pot or a good sun and low humidity after a front to dry the soil. I suggest that you remove most of the moss so that you can see and feel the soil in order to determine how dry it is. (Moss growing on the trunk or roots will cause the bark to rot also) An automatic watering system will be an aid but you should not rely on it to replace hand watering. Hand watering allows you to adjust the watering for each tree individually.
By John Miller - Reprinted From 2015