If you want to get your roses to bloom at a specific date, e.g. for a party at home, a wedding etc. then good luck!
By that I mean there is a certain amount of hit and miss – due to variables such as weather and the season, plus the health of plants and soil. The last two you can do something about, the first though are not within your control.
And, I am talking about home gardens – not those grown in a controlled climate like in hothouses etc.
All is not lost – roses bloom in a 6 to 8 week cycle generally (from pruning to open blooms) so you can usually hit your date broadly if you plan the pruning to aim for a date in the middle of that period. This does get a bit awry if the weather plays up – e.g. a cold period in spring or even mid-summer – though with the latter, the soil is usually warm enough to compensate.
The different types of roses also are a factor in the timing.
Hybrid Teas: 45 – 50 days
Floribundas: 50 – 55 days
Miniatures: 35 – 45 days
English: 50 – 50 days
Keeping those times in mind, it is worth the effort to get your backyard brimming with colorful, fragrant actively growing roses to add a lush, natural ambiance that would cost you bundle to replicate for a wedding, garden party or other outdoor event.
As mentioned, the main factor that can muck up the timing is the weather – especially cold snaps or excessive heat spells. Roses will bloom earlier than desired under the latter condition.
Remember also – the first spring flush after winter may take longer if there is residual cold hanging around which will slow growth. This is both about the temperature externally and within the soil.
Follow your normal pruning practices – though if they do not fit with your planned date – then prune earlier.
For example: if you want full flowering in latish spring, then you may have to prune when the first spring blooming is still ongoing. (This again depends on your local climate – I am in a Mediterranean climate.)
Remember a harder prune will also take longer to develop new blooms – and a dead-heading type of pruning will bring blooms along quicker.
Bloom-cycle time increases by five days for every leaflet cluster you cut lower down the cane. If you have plants loaded with bloom, every cane needs to be cut, even if there are flowers in bloom or bud.
Hedge Your Bet
If you feel unsure about getting the timing right, then leave some of the buds on canes – that is spread out your pruning – separate pruning by two or three days.
Roses are hungry plants – so fertilize regularly – especially after a prune. Use sulphate of potash as a supplement – to promote flower growth. Mulch and good soil also are vital.
This regime only applies to repeat flowering roses – those that only flower once in a season (e.g. ramblers, some old fashioned, Knock Outs) will not re-bloom after a pruning until the next season.