March has been a month of showery, though still warm, weather. As I write this today, a cool wind is blowing outside heralding the start of the colder seasons ahead. As usual for me, the time I spend working in my collection at this time of year has included plenty of weeding and general pruning to tidy unruly summer growth on my trees.
While the weather remains warm in April, it’s a good time to repot many species, particularly evergreens like pyracantha, cotoneasters, olives and star jasmine etc. Be aware though, that recently repotted trees will need protection if the nights suddenly become cold within the first couple of weeks after repotting.
You should leave any recent growth on deciduous species in autumn, waiting til late winter or repotting time to prune back the branches. Deciduous trees remove nutrients from their leaves during autumn to store over the winter months and eventually use in spring for new growth, so it’s best to ‘leave them to it’ for now.
During this season you can tidy up conifers. Check any branches that have been wired over summer to see if the design has set and to check that the wire isn’t cutting in. Remove any dead or overly dense foliage on junipers and reduce the needles on species such as pines or cedars by cutting or plucking off any that are on the undersides of branches. Remove unwanted candles as well on pines, leaving no more than two at any junction. These practices will make your trees look tidier and allow winter sunshine to better penetrate the foliage.
It’s now too late to prune back figs, and they should be left until the warmer spring weather returns later in the year. It’s still okay though, to remove any large leaves that are spoiling the design. While the weather is still warm maximize the amount of sunlight they receive, but if the nights become cold move to a more sheltered spot, particularly for more tropical species. Sudden temperature changes can make some Ficus, such as benjamina, drop their foliage, which is not what you want to happen at all.
Keep fertilising to build up strength for your trees to handle the colder months ahead. Use low nitrogen food to prevent a rush of soft new growth, however, as this may be damaged over winter. Feeding of deciduous species, while they are still green, is particularly important to maintain health in the tree before their winter dormancy. Sunny days and cool dry nights will hopefully enable maples and Liquidambars to show a lovely display of autumn colour before the leaves fall.
Autumn is a good time to do any wiring on trees, as the tree’s growth is generally slower over autumn/winter and the wire can be safely left in place for longer. Over winter branch girth does not increase significantly in most species. Wiring done in spring, on the other hand, needs to be constantly checked, or unsightly cutting in can happen alarmingly quickly.
Watering can most likely be reduced at this time, as the heat of the sun has eased off somewhat, but be alert nonetheless, particularly if it suddenly becomes windy. Using an open mix to grow your trees in is ideal for many reasons, but one of the drawbacks of good drainage can mean that the media is prone to drying out quickly on a windy day. Remember that your trees need to be checked every day, as they depend on you to fulfill all their needs. The consequences of them drying out, even for a short time, can be very difficult to overcome.
Continue to monitor your trees for insect attacks and respond accordingly. Particularly if your collection is in a sheltered area of your garden, pests can continue to thrive there, even as the weather becomes cooler. If your trees are kept well-spaced and tidy it’s easier to spot the infestation before it spreads.