Do I have to trim them down for the winter and put mulch around them. do I have to cover them. Is there any other care they need for the winter in northern Illinois'
Vanilla Strawberry (VS) is a panicle hydrangea that is winter hardy two zones below your zone 5b zone so VS will be fine with just mulching (3-4” of organic mulch past its estimated width or past the current drip line, whichever is further) and watering until temperatures are below freezing. Until it goes dormant and drops leaves, just water (if dry at a depth of 4") at 'spring watering levels' and mulch. Once it goes dormant, reduce watering to ‘dormancy levels’ if dry at a depth of 4” as there will be no more leaves needing water but stop watering once temperatures are always below freezing when you water or if the soil freezes; resume watering at ‘spring watering levels’ once the soil is dry at a depth of 4” and the soil has thawed and temperatures are above freezing. VS does not typically need pruning but if you need to prune, do not do it close to your average date of first frost (the 3rd-4th weeks of October) as pruning is an activity that can put the shrub in “grow mode” and the plant should be going dormant now instead. Alternatively, prune either much earlier, prune after the plant is fully dormant or prune as late as late winter/early spring or do not prune if there is no need. Fertilize with a slow-release fertilizer by your average date of last frost (the 1st-2nd weeks of May) and stop fertilizing 3 months before your average date of first frost (the average date is around the 3rd-4th weeks of October so stop fertilizing around the 3rd-4th weeks of July).
Venice is a compact Big Leaf Hydrangea that only produces one flush of blooms in spring from dormant, spring 2024 flower buds developed inside the ends of the stems somewhere around July-September 2023. Big Leaf Hydrangeas are best planted where they can attain they estimated dimensions and hardly pruned as they tend to often be either blooming, developing flower buds or carrying dormant flower buds that open in spring. To ensure reliable blooms, you may consider winter protecting the stem ends or you can grow it in a container that gets brought into a protected area like a garage/basement/etc. from your average date of first frost (the 3rd-4th weeks of October) through your average date of last frost (the 1st-2nd weeks of May). This species of hydrangea breaks dormancy in two stages. First, it develops new stem growth. Second, any live old wood leafs out a month or more afterwards (avoid prematurely pruning the leafless old wood until after the end of June in IL). Should it ever need pruning to control size, consider using rejuvenation pruning when dormant or consider pruning during a narrow time as it stops opening new blooms but before it begins developing dormant spring flower buds from July-September. Fertilize by your average date of last frost (the 1st-2nd weeks of May) and stop fertilizing 3 months before your average date of first frost (the 3rd-4th weeks of October). You can amend the soil to acidify it while the soil has not frozen; once frozen, stop amending with either garden sulfur or aluminum sulfate and re-start after the soil thaws.
Blueberry bushes are also very winter hardy and rarely require winter protection unless mild winters and wildly fluctuating temperatures make the bush break dormancy. If that were to occur, you can water deeply (if the soil is not frozen and if it is warm enough to water), cover the plant and mulch it.