When the Forsythia are blooming it is time to:
1) Spread pre-emergent herbicide on your lawn, if you do it at all.
2) Divide Hostas and most other perennials.
3) Fertilize your bushes, if you do it at all.
4) Prune your bushes, which you really ought to do if it has been more than a couple years.
1) Lawn Work
If, unlike me, you care about having a green, uniform grass lawn, you may choose to spread pre-emergent herbicide on your lawn. Such chemicals kill the sprouting seeds which annual weeds rely upon to regenerate, but do not kill lawn grass or other perennials. Still, they are potentially toxic chemicals. Except for corn gluten. Regular corn gluten is an effective pre-emergent herbicide, which also provides Nitrogen and Phosphorus (NPK of 9-1-0). It is sold in garden centers, but not, the last time I looked, in places like Home Depot. If you are to use corn gluten or any pre-emergent herbicide, you really should do it this weekend, before most of the weeds have sprouted.
2) Divide Hostas
Most Hostas are an inch or two tall as of today. It’s easy to see where they are, and even which ones are variegated, dark blue, etc. Now is the time to cut a chunk out of a Hosta, and plant it somewhere else, preferably with half-sun or less, in rich and humusy earth. (A week ago was fine too, but the job becomes much more destructive of the plants once they are all up and flopping about.) Fill the hole up with rich soil, or soil mixed with composted cow manure, water immediately, and water every couple days in dry weather (which we have been having).
Most other perennials can be similarly treated. There are perennials which don’t like to be disturbed, but all those which spread, and/or form “donut” shapes by expanding while their middle goes into decline, are suitable for propagation by shovel, and most even benefit from the shovel and subsequent soil enrichment. (Throw out the dead middle of any donut-shaped plant.)
3) Fertilize Bushes
This is most important with sheared plants such as hedges and most foundation plantings of yew, because shearing removes a lot of nutrients over time. But most shrubs in most locations would benefit from some fertilizer, be it a top-dressing of composted cow manure, some other rich compost, or a granular product (ideally, with at least some leaf compost or peat moss or a natural bark mulch which can break down and add organic material to the soil). If you have Rhododendrons (that includes azaleas), Pieris/andromeda, Kalmia/mountain laurel, Vaccinium (e.g., blueberry) and Erica & Calluna/heath & heather (apart from variegate Euonymous, most broad-leaved evergreens are in this family, the Ericaceae), then I recommend the Holly-Tone acidifying fertilizer, especially if you garden in a limestone area, such as most sites in the Northern Berkshires. Read the instructions. Don’t apply more than recommended. Instead, apply that amount, or half as much. You may repeat such treatment in early summer, but for most plants this second treatment should not be delayed past mid-July, lest you encourage lush growth which will fail to harden before an early frost. Note that many shrubs, notably Rhododendrons, have very shallow roots, so you should not try to dig fertilizers in.
4) Prune Bushes – Especially Hydrangeas
Pruning bushes is especially important for those with a tendency to build up congested and dead wood, such as most Hydrangeas. But almost any shrub needs pruning if it hasn’t gotten it in the last 2 or 3 years.
Pruning is needed for a number of overlapping reasons:
To remove dead, diseased or damaged wood
Remove rubbing or crossed branches
Open up the center to air and light
Make physical space for new buds to grow
Increase flowering or fruiting
Remove non-variegated reversions
Make the shrub more compact or a certain shape, to fit a spot or allow views out a window.
Make the shrub more compact, to look less scraggly
Deal with a fungal, bacterial or insect problem
Don’t Fear Radical Pruning
Even more so than with carpentry, there are several tools for removing wood, none for putting it back. But shrubs are far more forgiving than trees. You don’t have to worry about making multiple cuts so the branch won’t tear out of the trunk. You don’t have to worry about killing yourself. And you don’t have nearly as much reason to worry even about killing the plant. Shrubs aren’t just smaller than trees, they also tend to have multiple stems, and the ability to readily sprout new stems from the ground or close to the ground.
It is very hard to kill a shrub or permanently make one ugly due to pruning. Cutting a shrub all the way to the ground could kill it if hot dry weather ensues and you don’t water it daily, or if the shrub has no dormant buds near its base. But any shrub without such buds would be short-lived anyway, as it would not be able to replace old or damaged stems (e.g., lavender and some other woody herbs, and brooms, quick-growing plants most of which aren’t reliably hardy here anyway.)
There are a few rules to follow, but usually there’s no need to commit to a particular course of action when you start pruning. You first cut out the dead wood, clean out any refuse, and remove any intruders (weeds, seedlings, aggressive neighbors). With the lines of the shrub’s living wood revealed, you may now see that it’s a hideous misshapen mess. In that case, you may go straight to “radical pruning” – to cutting the plant to within an inch of the ground, or to a foot or so of trunk for those with a single trunk at their base (Rhodies, again). More likely, you’ll be merciful to the plant, because a hideous bunch of stems in April can still become a beautiful shrub once it’s leafed out and made new growth. But you will likely see that the remaining plant could still be reduced by a third (or perhaps even two-thirds). So you will remove some of the oldest stems (thicker, or with rougher bark), and you will remove stems with ugly scars or possible signs of disease or infestations.
If the plant is in leaf, and has leaves which are variegated or in colors other than green, you should remove any reversions to solid green. Most variegated cultivars will show such reversions over time. Even if you like the striking combination of areas of green contrasting with areas of a finer two-tone look, it is often best to remove the sold-green leaves since they will likely out-compete the rest of the plant.
For shrubs, like most Hydrangeas, with branches sprouting from the ground, almost all of your cuts will be to the ground. Easy, apart from the possible difficulty of reaching your clippers into the space. For other shrubs, with one or a few trunks which divide as they go up, you will be cutting higher up. Just remember not to cut a branch to some random point along its length, or to where you think that will make the shrub the right overall size. Instead, cut to where the branch sprouts from a larger branch, to just outside any branch collar (the swelling around the base of a branch).