May in the Garden

As far as I can tell, at the time of writing, we seem to have had a pretty ‘bright’ start to the growing season, with greater than average levels of sunshine and dry weather during March and April. Of course, every year is different but growth does appear to be somewhat ahead of schedule right now. May may be the first month when things really heat up but, equally, if it turns unseasonally cold and wet it can wreak real havoc to all the plants which have produced lots of delicate new growth and burgeoning buds.
The bright weather during April was accompanied, naturally, by overnight frosts which would have wiped out any tender plants which had been, inadvisedly, planted out too early. This month, however, they should be safer but, as ever, keep a weather eye open and be ready to cover them in a duvet of horticultural fleece if unseasonally cold nights are forecast.
For the same reason, any dahlia tubers which were potted up last month are probably best kept in pots, for now, and grown on a little longer, under protected conditions, until there is no chance that they will succumb to drops in overnight temperature. From mid-month onwards it should be safe to plant them out into the cutting garden, container displays and your flower beds.
The process of taking tender plants outside during warm, daytime temperatures and then returning them to a greenhouse, or cold frame, to avoid dangerously cold overnight temperatures, is known as ‘hardening off’. It’s a bit of a faff, especially if you have dozens of dubiously hardy plants waiting to be planted out, but it’s important for a whole load of plants which brighten up the summer garden.
For example, many of the salvia tribe are too dodgy to be planted outside year-round, generally succumbing to winter cold / wet even in relatively sheltered conditions, so keeping large specimens in pots is a good insurance policy. I find this especially useful for varieties of salvia from the species such as Salvia leucantha, S. confertiflora and S. guaranitica. They reach an impressively large size, forming woody bases, if kept protected from winter rotting and can be ‘stooled’, at the end of each growing season, to keep them ‘manageable’ in large pots for overwintering.
Shrubs which flowered early in the spring can be pruned, for shape and vigour, now that their flowers have faded, using the ‘one in three’ method. The ‘one in three’ refers to the ideal where you identify the oldest, most senile, one third of the stems and remove them right down to the base. You will remember, many moons ago, that I suggested that a tiny folding, Japanese pruning saw, fitting comfortably into the palm of your hand, was a favourite gift for gardeners—now’s the time that it comes into its own!
You’ll need a tiny saw in order to get right down into the base of an old shrub, where loppers are simply too bulky to do a proper job of cleanly excising old, thick, woody stems. Secateurs are generally not strong enough to cut through this kind of material and you may even damage the blades, or your hands, if you try forcing them beyond their capabilities. If you prune out the oldest stems, shrubs never get the chance to become elderly and are comprised of one, two and three year old wood to provide the best balance between vigour and flowering potential.
Pruned shrubs, like all plants which are attempting to make new growth, will benefit from an application of a good general fertiliser; ‘fish, blood and bone’ remains my ‘go to’ favourite but other, balanced, formulations are available. All this new growth will, in the case of herbaceous perennials, need supporting if you haven’t done so already. Insert pea-sticks around floppy herbaceous plants early in the month because the longer you leave it the more difficult it is to weave the supports in without damaging the soft, new, shoots.
Following on from where I left off last month; pests will be on an exponential increase so looking out for them, before they reach damaging levels, is the name of the game. Resorting to chemical control is generally frowned upon, naturally, so manually removing pests is the best way to keep them in check until their natural pest controlling predators can take over the job. Some pests, like aphids, can be blasted off their host plants, often roses, with well aimed jets of water but this cannot really be done on very soft foliage or on a whole garden scale.
As things warm up ponds and water gardens can be spruced up by removing overgrown aquatic plants and re-establishing the balance between the amount of plant cover and the area of open water. Ideally there should be at least two thirds open surface, even more for larger bodies of water, to maintain pond health. I find that this is hard to achieve in smaller ponds especially where ‘duckweed’ has taken over. I have no magic solution to duckweed; skimming as much as possible off, using a fine mesh fishing net, is all I ever do, to little effect, but this is not really feasible for large ponds. Deep pools, where the water nutrient levels are less likely to promote duckweed growth, are less likely to succumb to it.
Garden ponds are generally not deep enough to prevent big variations in water temperature and nutrient levels, which makes keeping the water clear of excessive weed growth or filamentous algae particularly difficult. When removing unwanted pond plants, or accumulated detritus, remember that this should not be dumped in the wild, especially not into wet areas, because a lot of non-native pond plants are designated ‘invasive species’ and must not be introduced into UK countryside. Composting within your garden, if you have room, should be safe, other wise it will need to be bagged up and taken, as ‘green waste’, to your local recycling centre / amenity dump.